FUNCTIONAL ANATOMY OF LARGE INTESTINE

FUNCTIONAL ANATOMY OF LARGE INTESTINE

Large intestine or colon extends from ileocecal valve upto anus .

PARTS OF LARGE INTESTINE

Large intestine is made up of the following parts:

1. Cecum with appendix

2. Ascending colon

3. Transverse colon

4. Descending colon

5. Sigmoid colon or pelvic colon

6. Rectum

7. Anal canal

STRUCTURE OF WALL OF LARGE INTESTINE

Wall of large intestine is formed by four layers of structures like any other part of the gut.

1. Serous layer: It is formed by peritoneum

2. Muscular layer: Smooth muscles of large intestine are distributed in two layers, namely the outer

longitudinal layer and inner circular layer. The longitudinal muscle fibers of large intestine are

arranged in the form of three long bands called tenia coli. The length of the tenia coli is less when

compared to the length of large intestine. Because of this, the large intestine is made into series of

pouches called haustra 3. Submucus layer: It is not well developed in large intestine

4. Mucus layer: The crypts of Leiberk├╝hn are present in mucosa of large intestine. But the villi, which are

present in mucus membrane of small intestine, are absent in the large intestine. Only mucus-secreting

glands are present in the mucosa of large intestine.

SECRETIONS OF LARGE INTESTINE

Large intestinal juice is a watery fluid with pH of 8.0.

COMPOSITION OF LARGE INTESTINAL JUICE

Large intestinal juice contains 99.5% of water and 0.5% of solids. Digestive enzymes are absent and

concentration of bicarbonate is high in large intestinal juice.

FUNCTIONS OF LARGE INTESTINAL JUICE

Neutralization of Acids

Strong acids formed by bacterial action in large intestine are neutralized by the alkaline nature of large intestinal juice. The alkalinity of this juice is mainly due to the presence of large quantity of bicarbonate.

Lubrication Activity

Mucin present in the secretion of large intestine lubricates the mucosa of large intestine and the bowel

contents, so that, the movement of bowel is facilitated. Mucin also protects the mucus membrane of

large intestine by preventing the damage caused by mechanical injury or chemical substances. FUNCTIONS OF LARGE INTESTINE

1. ABSORPTIVE FUNCTION

Large intestine plays an important role in the absorption of various substances such as:

i. Water

ii. Electrolytes

iii. Organic substances like glucose

iv. Alcohol

v. Drugs like anesthetic agents, sedatives and steroids.

2. FORMATION OF FECES

After the absorption of nutrients, water and other substances, the unwanted substances in the large

intestine form feces. This is excreted out.

3. EXCRETORY FUNCTION

Large intestine excretes heavy metals like mercury, lead, bismuth and arsenic through feces.

4. SECRETORY FUNCTION

Large intestine secretes mucin and inorganic substances like chlorides and bicarbonates.

5. SYNTHETIC FUNCTION

Bacterial flora of large intestine synthesizes folic acid, vitamin B12 and vitamin K. By this function, large

intestine contributes in erythropoietic activity and blood clotting mechanism.

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