Structure and Function of the Large Intestine

The large intestine is a continuation of the ileum and is usually divided into three regions: the colon, rectum and anal canal. The colon accounts for nearly the full length of the large intestine. The colon absorbs water and electrolytes (approximately 1400 ml per day). It also compacts and eliminates feces (about 100 ml per day). Feces are composed of water (75%), dead bacteria (7%), roughage (5%), inorganic substances (5%), and undigested protein, dead cells and bile pigment (1%). Bacterial products, including the vitamins riboflavin, thiamin, vitamin B12 and vitamin K, are also excreted in the feces (5).

The colonic mucosal membrane does not have any folds due to an absence of villi (Fig. 2). The intestinal glands are long and characterized by a great abundance of goblet and absorptive cells, and a small number of enteroendocrine cells. The large intestinal epithelium is specialized for mucos secretion, salt and water absorption.

The histology of the rectum is identical to that of the colon except that the crypts of Lieberkuhn are deeper and fewer in number. The rectum is about 12-18 cm in length and is continuous with the anal canal, which spans about 3 to 4 cm. The mucosa of the anal region displays a series of longitudinal folds, the rectal columns of Morgagni. These rectal columns meet one another to form pouch-like outpocketings, the anal valves with intervening anal sinuses. The anal valves assist in supporting the column of feces (5). The epithelial cells of the entire gastrointestinal tract are constantly shed. They are replaced with stem cells that have undergone mitosis. The high turnover rate of the epithelial cells may explain why the small intestine is affected rapidly by the administration of

Large Intestine Problems

Colonic epithelium

Lamina propria

. Muscularls mucosae

Muscularls externa

Submucosa

Figure 2 Schematic diagram of the colonic epithelium and associated cells.

Colonic epithelium

Lamina propria

. Muscularls mucosae

Muscularls externa

Figure 2 Schematic diagram of the colonic epithelium and associated cells.

Submucosa anti-mitotic drugs, as in cancer chemotherapy. The epithelial cells continue to be lost at the tip of the villi, but drugs inhibit cell proliferation (6).

Pregnancy And Childbirth

Pregnancy And Childbirth

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