Blood is the vehicle of the cardiovascular system.
Thus, it is the component which actually transports substances.
Blood is composed of the following:
• Formed elements
Plasma – Water Component
Plasma makes up about 55 percent of the total blood volume.
The major constituent of plasma is water.
The physical characteristics of water make it a very good vehicle for the following reasons:
• water is fluid therefore it can flow through the conduits.
• most substances can be dissolved in water, it is often known as the "universal solvent."
• at ordinary pressures, water is essentially non-compressible.
Plasma – Water Component
In addition, water has important temperature characteristics.
Water has an ample heat-carrying capacity. It can carry heat readily throughout the body.
Some of this heat is transferred to the water of the sweat glands.
Since water can dissipate great quantities of heat through evaporation, excess heat can
be efficiently disposed of at the surface of the skin.
Plasma – Dissolved and Suspended substances
To some extent, all transported substances are dissolved or suspended in the water of the plasma.
These substances include:
• various gases
• end products of digestion
• various control substances
• waste products
• three major plasma proteins--albumin, globulins, and fibrinogen
• dissolved salts (electrolytes)
Together with the dissolved salts (electrolytes), the plasma proteins help to maintain the tonicity of the plasma. In addition, fibrinogen is important to blood clotting.
The remainder of the blood volume consists of the formed elements:
• red blood cells
• white blood cells
In adults, these formed elements normally make up 40 percent to 45 percent of the total blood volume.
This measure is called the hematocrit.
Red Blood Cells
Red Blood Cells are also called RBCs or Erythrocytes.
Hemoglobin is a special protein which is found within the RBC cytoplasm.
Because of its iron atoms, hemoglobin has a great affinity for oxygen.
It will readily pick up oxygen until it is saturated.
At the same time, however, hemoglobin will readily give up oxygen in areas of low concentration.
The primary function of RBCs is to carry oxygen to the majority of the oxygen to the individual cells of the body.
Structure of Red Blood Cells
The normal, mature red blood cell is a biconcave disc.
The biconcave shape results from the loss of the nucleus just before the final maturation of the RBC.
Since this shape increases the surface area of the disc, there is an increase in the capacity for the flow of substances into and out of the RBC.
The Life Cycle of the Red Blood Cell
Because of the loss of its nucleus, the RBC has a limited life period (about 120 days).
At the end of this period, the spleen removes the "worn out" RBC, and the liver salvages the "pieces," particularly the iron.
White Blood Cells
White blood cells are another of the formed elements of the blood, they are also known as WBCs or Leucocytes.
There are several types of WBC. Neutrophils, Monocytes and other phagocytic WBCs. Some phagocytic WBCs can move independently out of the capillaries and penetrate into the tissues of the body.
There, they actively attack foreign substances and engulf them in a process called phagocytosis. When these WBCs are overcome by foreign substances and die, their bodies accumulate to form a substance called pus.
Lymphocytes are another type of WBC. They are involved with the immune system of the body, including the production of antibodies.
The platelets are the third type of formed element in the blood.
Platelets are fragments of former cells.
They play an important role in the clotting process.
While blood plasma is whole blood minus the blood cells, serum is whole blood minus the cells and minus fibrinogen and other clotting factors. ??????????????
A clear pale straw colored fluid called serum remains after blood has been treated to remove the formed elements and the protein fibrinogen.