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Module 1: Módulo 4: Digestão, absorção, eliminação e proteção

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Digestion involves the breakdown of foodstuffs into their basic constituents.

The small intestines are the primary area of the body for digestion of foodstuffs.

The end-products (molecules or particles) of digestion are small enough to be absorbed through the walls of the small intestines.

These end-products are then distributed throughout the body by the body's circulatory systems.

Page 2 Digestion as a Chemical Process
Digestion is the chemical process.

In general, chemical processes are expected to occur at a rate proportional to the temperature.

However, in the human body, the temperature is not high enough for the chemical process of digestion to produce a sufficient quantity of the materials needed.

Therefore, digestive enzymes are present to maintain the appropriate rates of reaction.


Page 3 Digestive Enzymes
Digestive enzymes are catalysts. A catalyst is a substance that improves the rate of a reaction without being consumed itself.

The molecule upon which an enzyme acts is called a substrate.


Because of digestive enzymes, digestion proceeds at a pace fast enough to provide the materials needed by the body.

Page 4 Digestive Enzymes
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Foodstuff Enzyme Class End Product
Carbohydrate Amylases Simple Sugars
Lipid Lipases Fatty Acids
Proteins Proteases Amino Acids
Table of foodstuffs, enzyme classes, and end-products of digestion.

Page 5 Digestion in the Mouth and Stomach
The digestive process begins in the oral cavity.

The saliva contains enzymes which initiate the digestion of complex carbohydrates.

In the stomach, the gastric glands produce enzymes that initiate the digestion
of proteins.

Page 6 Digestion in the Small Intestine
The majority of digestion in humans takes place in the small intestines.

The small intestines are located in the central part of the abdomen, immediately beneath the
abdominal wall.

In healthy individuals, a flap called the greater omentum is draped over the small intestines (between them and the anterior abdominal wall).

The greater omentum has a great deal of fat for insulation. It is richly supplied with blood vessels for
heat. Some might compare the greater omentum to an "electric blanket" for the small
intestines.

Page 7 Digestive Enzymes in the Small Intestine
In the small intestines, there are digestive enzymes for all three classes of foodstuffs - carbohydrates, lipids, and proteins.

Enzymes for completing the digestion of these three classes are found in the fluids produced by the pancreas and glands in the mucosa of the small intestines.

Moreover, there is a fluid called bile that is produced by the liver and stored in the gallbladder for release into the small intestines.

Bile helps in the digestion of lipids.

Page 8 Time and Length
The length of the small intestines appears to be just right.

The time it takes for material to travel from beginning to end is just about right for the completion of
digestion.