Small Intestine

A long tube, with a small diameter (about 1 inch), extending from pyloric sphincter to the ileocecal valve .

Divided into Duodenum, Jejunum, and ileum.

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b. ▪

Digestive enzymes embedded in the surfaces of microvilli split molecules of sugars, proteins and fats .

c. Regulation of small intestine secretions: secretion is stimulated by gastric juice , chyme , and reflex stimulated by distension of the small intestinal wall .

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d. ▪

Each villus contains blood capillaries to absorb water , glucose , amino acids , vitamins , minerals , and short-chain fatty acids , and also contains lymphatic capillaries called lacteals to absorb long – chain fatty acids in the forms of micelles .

e. Water is absorbed by osmosis , fatty acids are absorbed by diffusion (since they are fat-soluble), and most other nutrients (glucose, amino acids, & minerals) are absorbed by active transport.

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Large intestine

The last segment of the GI tract , with a large diameter (2-3 inches) , extending from the ileocecal valve to the anus .

Divided into cecum , ascending colon , transverse colon , descending colon , sigmoid colon , rectum , anal canal , and anus.

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The ▪

large intestine has little or no digestive function , although it secretes mucus. Its mucosa has no villa or microvillus , but cotains numerous goblet cells for secreting mucus to aid in the formation of feces and maintain an alkaline condition .

mechanical stimulation and parasympathetic impulses control the rate of mucus secretion .

The large intestine only absorbs water, electrolytes and some vitamins .

Many bacteria inhabit the large intestine , where they break down certain indigestible substances and synthesize certain vitamins .

feces are formed and stored in the large intestine . Defecation involves a reflex mechanism aided by voluntary contraction of the diaphragm , abdominal muscles ,and the external anal sphincter .

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings