Small intestine

 

Chyme which enters the small intestine via the duodenum come in the intestine via peristaltic wave with a velocity of 0.5 to 2.0 cm/sec. It initially moves quite fast, mostly in the jejunum but slows down in the ileum and colon. 3 to 5 hours are required for transit between the ileocecal valve and the duodenojejunal junction or pylorus of the stomach. Increase in transit time in the small intestine is influenced for rapidity by the following factors

The peristalsis in the small intestine flattens the chyme against the wall of the mucosa in order to increase the contact between mucosa and chyme. But chyme is blocked at the ileocecal junction by the ileocecal valve and may not release the food into the cecum unless the individual takes another meal which by its gastroileal reflexes will then passage of chyme into the colon.

In the small intestine, a mechanism by which infected chyme or noxious substances are removed from the intestine is the peristaltic rush which causes through the autonomic nervous system, the rushing of peristaltic wave that delivers chyme in seconds into the colon for evacuation.

Aside from digestive mechanisms the role of the duodenum is major in inhibiting gastric emptying by hormonal and other factors. The enterogastric nervous system from the duodenum is worthy of mention in this regard. This is the so called enterogastric inhibitory reflexes in the duodenum which are initiated by the following

Secretions

Enterocytes which secrete watery intestinal fluid (succus entericus) and through their crypts of Libeberkühn absorb them back through the microvilli. They also secrete enzymes as follows

Hormones: Many gut hormone influence the functions of the various parts of the gut. Such influences include the processes of secretion of enzymes, contraction and peristalsis and absorption. They include

Gastrin

Secretin

Cholecystokinin-Pacreozymin

Glucagon

Gastric inhibitory peptide

Vasoactive intestinal peptide

Bombesin

Neurotensin

Substance P

 

 

 

 

 

 

 

 

 

 

 

 

Roll over mouse to demonstrate bowel sound

       

 
Cross section through small intestine

 

 

 

 

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