Section V. THE LARGE INTESTINES
1-10. GENERAL FUNCTION
The primary function of the large intestines is the salvaging of water and
electrolytes (salts). Most of the end products of digestion have already been absorbed
in the small intestines. Within the large intestines, the contents are first a watery fluid.
Thus, the large intestines are important in the conservation of water for use by the body.
The large intestines remove water until a nearly solid mass is formed before defecation,
the evacuation of feces.
1-11. MAJOR SUBDIVISIONS
The major subdivisions of the large intestines are the cecum (with vermiform or
"worm-shaped" appendix), the ascending colon, the transverse colon, the descending
colon, and the sigmoid colon. The fecal mass is stored in the sigmoid colon until
passed into the rectum.
1-12. RECTUM, ANAL CANAL, AND ANUS
Rectum means "straight". However, this six inch tubular structure would actually
look a bit wave-like from the front. From the side, one would see that it was curved to
conform the sacrum (at the lower end of the spinal column). The final storage of feces
is in the rectum. The rectum terminates in the narrow anal canal, which is about 1 1/2
inches long in the adult. At the end of the anal canal is the opening called the anus.
Muscles called the anal sphincters aid in the retention of feces until defecation.
Section VI. ASSOCIATED PROTECTIVE STRUCTURES
Within the body, there are many structures that aid in protection from bacteria,
viruses, and other foreign substances. These structures include cells that can
phagocytize (engulf) foreign particles or manufacture antibodies (which help to
inactivate foreign substances). Collectively, such cells make up the reticuloendothelial
system (RES). Such cells are found in bone marrow, the spleen, the liver, and lymph
1-14. STRUCTURES WITHIN THE DIGESTIVE SYSTEM
Lymphoid structures make up the largest part of the RES. Lymphoid structures
are collections of cells associated with circulatory systems.
a. Tonsils are associated with the posterior portions of the respiratory and
digestive areas in the head, primarily in the region of the pharynx. The tonsils are
masses of lymphoid tissue.