Anatomy and Physiology of the Large Intestine PDF

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Anatomy and Physiology of the Large Intestine...

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Anatomy and Physiology of the Large Intestine •

The functions of the large intestine are the absorption of water, the manufacturing and absorption of certain vitamins, and the formation and expulsion of the feces.

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The large intestine is about 5 feet in length and averages 2.5 inches in diameter.

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Also referred to as the bowel.

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It is attached to the posterior wall of the abdomen by extensions of its visceral peritoneum known as the mesocolon.

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It is divided into 4 principal regions: 1. The cecum, the pouch-like part of the large intestine. 2. The colon, the largest part. 3. The rectum 4. The anal canal

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The opening from the ileum of the small intestine into the cecum of the large intestine is a fold of mucous membrane known as the ileocecal valve. § This valve allows material to pass from the small intestine into the large intestine.

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The cecum, a blind pouch (one end is closed), is 2 to 3 inches long and hangs below the ileocecal valve.

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Attached to the closed of the cecum is the twisted tube known as the vermiform appendix, about 3 inches in length.

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The open end of the cecum merges with the long tube called the colon.

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The colon looks like a tube of consecutive pouches. The pouches are called haustrae.

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The first part of the colon is knowns at the ascending colon. § It rises on the right side of the abdomen, reaches the undersurface of the liver, and turns to the left at the right colic (hepatic) flexure.

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The right colic flexure continues across the abdomen to the left side as the transverse colon.

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It then curves beneath the lower end of the spleen to the left side as the left colic (splenic flexure.

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Next, it passes downward as the descending colon.

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The last part of the colon is called the sigmoid colon, where the colon joins the rectum.

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3 mechanical movements occur in the large intestine: § Haustral churning

Anatomy and Physiology of the Large Intestine § §

Peristalsis at the rate of 3 to 12 contractions per minute Mass peristalsis

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Food in the stomach initiates mass peristalsis, which is a strong peristaltic wave that begins in the middle of the transverse colon and drives its contents into the rectum

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The rectum is the last 7 to 8 inches of the gastrointestinal tract. § It is situated anterior to the sacrum and the coccyx. § The terminal 1 inch of the rectum is called the anal canal.

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The mucous membrane of the anal canal is arranged in a series of longitudinal folds called the anal columns that contain a network of arteries and veins.

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The opening of the anal canal to the exterior is called the anus. § It is guarded by an internal sphincter of smooth muscle and an external sphincter of skeletal muscle.

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The absorption of water is an important function of the large intestine. In addition, bacteria in the colon manufacture 3 important vitamins that are also absorbed in the colon: vitamin K needed for clotting, biotin needed for glucose metabolism, and vitamin B5 needed to make certain hormones and neurotransmitters.

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Mucus is also produced by glands in the intestine.

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Intestinal water absorption is greatest in the cecum and ascending colon.

Figure 16-14 The anatomy of the large intestine.

Anatomy and Physiology of the Large Intestine...