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Comments about Global health - Global health: oral rehydration therapy

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- Module: Global health
- Topic: Global health: oral rehydration therapy

Latest Comments

  • amber shami United States of America Oral rehydration therapy is one of bet and low cost treatment
    2014-12-08 07:12:33

  • Sharlene Fryer New Zealand flat lemonade and salty crackers works well too
    2014-11-24 21:11:06

  • Azam Md.Nur-E-Azam Bangladesh oral re hydration therapy is nice to me
    2014-11-19 10:11:49

    • Kassech Moltumo Australia oral re hydration preparation is very simple and can be made at home
      2014-12-16 08:12:42
  • Hafsah Danmusa Nigeria What is oral rehydrating therapy
    2014-11-07 20:11:37

  • Hafsah Danmusa Nigeria Go a good living it's requires,..carbohydrate.....vitamin....calcium.
    2014-11-07 20:11:36

  • Evelyn Mkangi Kenya This form of ORS is very common in homes before a child is taken to hospital. Sometimes even live saving
    2014-10-28 11:10:42

  • Clarissa Bartholomew United States of America Oral rehydration therapy could be increased if people were more educated about it.
    2014-10-27 19:10:20

  • Zeeshan Jawed Australia Global health: oral rehydration therapy Oral rehydration therapy Unsafe water and lack of sanitation usually cause diarrhoea. In developing countries, a child with diarrhoea will usually die from the loss of water and electrolytes. To overcome this by intravenous rehydration is a costly practice, requiring trained personnel and sterile equipment. As an alternative, oral rehydration can involve giving the child a solution of sugar and salts to drink and it is a much simpler and cheaper method
    2014-10-20 02:10:11

  • Zachary Bashore United States of America What is oral rehydration safe/ety?
    2014-08-22 03:08:51

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:51

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:30

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:09

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:38

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:19

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:49

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:10

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:50

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:30

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:06

  • Jones Hanungu Munang'andu Zambia Nutrition Each substance required for the nutrition of every cell in the body is transported by the blood: the precursors of carbohydrates, proteins, and fats; minerals and salts; vitamins and other accessory food factors. These substances must all pass through the plasma on the way to the tissues in which they are used. The materials may enter the bloodstream from the gastrointestinal tract, or they may be released from stores within the body or become available from the breakdown of tissue. The concentrations of many plasma constituents, including blood sugar (glucose) and calcium, are carefully regulated, and deviations from the normal may have adverse effects. One of the regulators of glucose is insulin, a hormone released into the blood from glandular cells in the pancreas. Ingestion of carbohydrates is followed by increased production of insulin, which tends to keep the blood glucose level from rising excessively as the carbohydrates are broken down into their constituent sugar molecules. But an excess of insulin may severely reduce the level of glucose in the blood, causing a reaction that, if sufficiently severe, may include coma and even death. Glucose is transported in simple solution, but some substances require specific binding proteins (with which the substances form temporary unions) to convey them through the plasma. Iron and copper, essential minerals, have special and necessary transport proteins. Nutrient substances may be taken up selectively by the tissues that require them. Growing bones use large amounts of calcium, and bone marrow removes iron from plasma for hemoglobin synthesis. Excretion The blood carries the waste products of cellular metabolism to the excretory organs. The removal of carbon dioxide via the lungs has been described above. Water produced by the oxidation of foods or available from other sources in excess of needs is excreted by the kidneys as the solvent of the urine. Water derived from the blood also is lost from the body by evaporation from the skin and lungs and in small amounts from the gastrointestinal tract. The water content of the blood and of the body as a whole remains within a narrow range because of effective regulatory mechanisms, hormonal and other, that determine the urinary volume. The concentrations of physiologically important ions of the plasma, notably sodium, potassium, and chloride, are precisely controlled by their retention or selective removal as blood flows through the kidneys. Of special significance is the renal (kidney) control of acidity of the urine, a major factor in the maintenance of the normal pH of the blood. Urea, creatinine, and uric acid are nitrogen-containing products of metabolism that are transported by the blood and rapidly eliminated by the kidneys. The kidneys clear the blood of many other substances, including numerous drugs and chemicals that are taken into the body. In performing their excretory function, the kidneys have a major responsibility for maintaining the constancy of the composition of the blood. (See also renal system.) The liver is in part an excretory organ. Bilirubin (bile pigment) produced by the destruction of hemoglobin is conveyed by the plasma to the liver and is excreted through the biliary ducts into the gastrointestinal tract. Other substances, including certain drugs, also are removed from the plasma by the liver. Immunity Cells of the blood and constituents of the plasma interact in complex ways to confer immunity to infectious agents, to resist or destroy invading organisms, to produce the inflammatory response, and to destroy and remove foreign materials and dead cells. The white blood cells (leukocytes) have a primary role in these reactions: granulocytes and monocytes phagocytize (ingest) bacteria and other organisms, migrate to sites of infection or inflammation and to areas containing dead tissue, and participate in the enzymatic breakdown and removal of cellular debris; lymphocytes are concerned with the development of immunity. Acquired resistance to specific microorganisms is in part attributable to antibodies, proteins that are formed in response to the entry into the body of a foreign substance (antigen). Antibodies that have been induced by microorganisms not only participate in eliminating the microbes but also prevent reinfection by the same organism. Cells and antibodies may cooperate in the destruction of invading bacteria; the antibody may attach to the organism, thereby rendering it susceptible to phagocytosis. Involved in some of these reactions is complement, a group of protein components of plasma that participates in certain immunologic reactions. When certain classes of antibodies bind to microorganisms and other cells, they trigger the attachment of components of the complement system to the outer membrane of the target cell. As they assemble on the cell membrane, the complement components acquire enzymatic properties. The activated complement system is thus able to injure the cell by digesting (lysing) portions of the cell's protective membrane. Temperature regulation Heat is produced in large amounts by physiological oxidative reactions, and the blood is essential for its distributing and disposing of this heat. The circulation assures relative uniformity of temperature throughout the body and also carries the warm blood to the surface, where heat is lost to the external environment. A heat-regulating centre in the hypothalamus of the brain functions much like a thermostat. It is sensitive to changes in temperature of the blood flowing through it and, in response to the changes, gives off nerve impulses that control the diameter of the blood vessels in the skin and thus determine blood flow and skin temperature. A rise in skin temperature increases heat loss from the body surface. Heat is continuously lost by evaporation of water from the lungs and skin, but this loss can be greatly increased when more water is made available from the sweat glands. The activity of the sweat glands is controlled by the nervous system under direction of the temperature-regulating centre. Constancy of body temperature is achieved by control of the rate of heat loss by these mechanisms. Hemostasis The blood is contained under pressure in a vascular system that includes vast areas of thin and delicate capillary membranes. Even the bumps and knocks of everyday life are sufficient to disrupt some of these fragile vessels, and serious injury can be much more damaging. Loss of blood would be a constant threat to survival if it were not for protective mechanisms to prevent and control bleeding. The platelets contribute to the resistance of capillaries, possibly because they actually fill chinks in vessel walls. In the absence of platelets, capillaries become more fragile, permitting spontaneous loss of blood and increasing the tendency to form bruises after minor injury. Platelets immediately aggregate at the site of injury of a blood vessel, tending to seal the aperture. A blood clot, forming in the vessel around the clump of adherent platelets, further occludes the bleeding point. The coagulation mechanism involves a series of chemical reactions in which specific proteins and other constituents of the blood, including the platelets, play a part. Plasma also is provided with a mechanism for dissolving clots after they have been formed. Plasmin is a proteolytic enzyme—a substance that causes breakdown of proteins—derived from an inert plasma precursor known as plasminogen. When clots are formed within blood vessels, activation of plasminogen to plasmin may lead to their removal. (For additional information about the mechanics and significance of hemostasis, see bleeding and blood clotting.) Laboratory examination of blood Physicians rely upon laboratory analysis to obtain measurements of many constituents of the blood, information useful or necessary for the detection and recognition of disease. Hemoglobin contains a highly coloured pigment that interferes with the passage of a beam of light. To measure hemoglobin concentration, blood is diluted and the red blood cells (erythrocytes) broken down to yield a clear red solution. A photoelectric instrument is used to measure the absorbance of transmitted light, from which hemoglobin concentration can be calculated. Changes in the hemoglobin concentration of the blood are not necessarily directly paralleled by changes in the red cell count and the hematocrit value, because the size and hemoglobin concentration of red cells may change in disease. Therefore, measurements of the red cell count and the hematocrit value may provide useful information as well. Electronic particle counters for determining red cell, white cell (leukocyte), and platelet counts are widely used. Only a drop of blood is needed for the analyses, which are completed within a minute. Adequate examination of the blood cells requires that a thin film of blood be spread on a glass slide, stained with a special blood stain (Wright stain), and examined under the microscope. Individual red cells, white cells, and platelets are examined, and the relative proportions of the several classes of white cells are tabulated. The results may have important diagnostic implications. In iron-deficiency anemia, for example, the red cells look paler than normal because they lack the normal amount of hemoglobin; in malaria the diagnosis is established by observing the malarial parasites within the red cells. In pneumonia and many infections, the proportion of neutrophilic leukocytes is usually increased, while in others, such as pertussis (whooping cough) and measles, there is an increase in the proportion of lymphocytes. Chemical analyses measure many of the constituents of plasma. Often serum rather than plasma is used, however, since serum can be obtained from clotted blood without the addition of an anticoagulant. Changes in the concentrations of chemical constituents of
    2014-08-04 09:08:40

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