b. Vitamin D. Vitamin D is produced in the skin by the activity of solar radiation.
It is also present in fish liver oils, butter, and egg yolk.
c. Vitamin K. Vitamin K is important in blood clotting. It is actually produced by
microorganisms located in the large intestines. This source of vitamin K may be lost
during the administration of antibiotics. Vitamin K also occurs in such foods as alfalfa,
spinach, cabbage, and egg yolk.
d. Vitamin E. The function of vitamin E in humans is not known. Research
indicates that vitamin E has important functions in various species, but the specific
function varies from species to species.
Section VIII. ELIMINATION OF UNUSED MATERIALS
6-34. UNDIGESTED FOOD MATERIALS
a. Nondigestible Food Materials. A number of substances within food
materials cannot be digested by the human digestive system. One important material in
this group is called cellulose. Cellulose is a complex carbohydrate found in plants.
Cellulose is commonly referred to as "bulk" or "fiber."
b. Other Undigested Food Materials. When individuals consume great quanti-
ties of foods, a portion of it will not be digested.
c. Passage Out of the Small Intestines. This undigested material will pass out
of the small intestines with the non-digestible materials. The resulting fluid mass enters
the large intestines through the ileocecal valve.
6-35. LARGE INTESTINES
a. Consolidation of Contents. In the large intestines, this fluid mass is
gradually consolidated into a semisolid mass called feces. The major function of the
large intestines then is salvage. Water is the primary salvage item. In addition to water,
some previously unabsorbed endproducts of digestion can be absorbed here. At the
same time certain excretions from the body can be deposited in the fecal mass.
b. Mucus. As the contents increase in solidity, mucus is added to facilitate their
movement through the large intestines. (Previously, we have seen the addition of
mucus to the bolus in the mouth to facilitate movement.) This mucus is produced by
unicellular glands in the mucosal lining of the large intestines. (Because of their
microscopic appearance, these unicellular glands are called goblet cells.)