Download Topic 6: Human health and physiology

Topic 6: Human health and physiology
Key facts
Digestion
1. Food ingested must be digested in order to be useful to the organism. Without
digestion the food particles are too large to be absorbed through the villi of the small
intestine to enter the bloodstream.
2. Large macromolecules of food go through hydrolysis allowing the organism to obtain
necessary building blocks for assimilation. This hydrolysis is also necessary so that ATP
formation from the food is possible.
3. Assimilation is the process by which the products of food digestion become part of the
organism’s body.
4. Enzymes greatly aid the digestive process by causing it to proceed more rapidly.
5. Specific enzymes are produced at particular locations of the digestive system. These
enzymes act on certain substrates to bring about digestion.
6. Digestive areas of particular activity involving enzymes include the mouth, the
stomach and the small intestine.
7. Enzymes which are active in the stomach must have optimum pH values which are
quite acidic. Enzymes working in the small intestine must be able to work in a more
alkaline environment.
8. The mouth’s major enzyme producing glands are the salivary glands. The mouth has
a pH of near 7.
9. The salivary glands produce salivary amylase which allows hydrolysis of starch into
maltose.
10. The wall of the stomach produces the enzyme pepsin which breaks proteins down
into small polypeptides. The stomach has a pH of near 1.5.
11. The pancreas may function as an endocrine and as an exocrine gland. When it
functions as an exocrine gland it produces several enzymes. One is pancreatic lipase,
which is transported to the small intestine where it catalyzes the breakdown of
triglycerides (fats or oils) into fatty acids and glycerol. The pH of the small intestine is 7
or higher (slightly alkaline).
12. Digestion of proteins begins in the stomach. Also, the extremely acidic environment
of the stomach serves to destroy any incoming bacteria with the food.
13. Most of the digestion of food actually occurs in the small intestine. Enzymes active
in small intestine come from the pancreas and the walls of the structure itself.
14. Once digestion in the small intestine is finished, the smaller food products are
absorbed through millions of villi lining the interior of the small intestine. This
absorption occurs as a result of diffusion, facilitated diffusion, or active transport.
15. Villi bring about the process of absorption. They are small finger-like projections
from the small intestine wall. They are effective in food absorption due to their extreme
numbers, large surface area due to microvilli, capillaries near their surface and a centrally
located lacteal which allows absorption of fat digestion.
16. The indigestible parts of food mixed with large amounts of water pass to the large
intestine.
17. In the large intestine water is absorbed and indigestible parts of the food are passed as
feces through the anus.
18. The parts of the digestive system that food passes through are the mouth, esophagus,
stomach, small intestine, large intestine and anus. The liver, pancreas and gall bladder
are ancillary structures involved in the digestive process.
1. Draw and label a diagram of the digestive system. Include the following structures:
mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas, and gall
bladder.