Digestion 31-41

Digestion in the small intestine (31) Virtually all nutrient absorption takes place in the small intestine Chime is released slowly into the duodenum Mixing is required because chime is hypertonic and has low pH Required substances are supplied by the liver

Motility in the small intestine (31) The most common motion of the small intestine is segmentation Moves contents steadily toward the ileocecal valve After nutrients have been absorbed: Peristalsis begins with each wave starting distal to the previous Meal remnants, bacteria, mucosal cells, and debris are moved into the large intestine

The ileocecal valve is a sphincter muscle situated at the junction of the small intestine (ileum) and the large intestine.

Subdivisions of the large intestine (32) Cecum, appendix, colon, rectum and the anal canal

Vermiform appendix – now thought to house friendly bacteria

Regions of the colon (33) –ascending colon –hepatic flexure, –transverse colon, –splenic flexure, –descending colon –sigmoid colon

Large intestine

Why don’t we poop when we toot? (34) 3 valves of the rectum stop feces from being passed with gas

Anal sphincters – voluntary & involuntary (35) The internal anal sphincter is composed of smooth muscle (involuntary) The external anal sphincter is composed of skeletal muscle (voluntary)

Internal – smooth muscle External – skeletal muscle

Origin & significance of bacterial flora in the large intestine (36) Friendly! Bacteria surviving the small intestine that enter the cecum Bacteria entering from the anus These bacteria colonize the colon, ferment indigestible carbs, release irritating acids and gases (flatus), synthesize B complex vitamins and vitamin K

Function of the large intestine (37) Other than digestion of enteric bacteria, no further digestion takes place Vitamins, water, and electrolytes are reclaimed Propulsion of fecal material toward the anus is the MAJOR function You Tube video here

General protocol for defecation (38) Distension of rectal walls caused by feces: –Stimulates contraction of the rectal walls –Relaxes the internal sphincter Voluntary signals stimulate relaxation of the external anal sphincter and defecation occurs

How nutrients are digested & absorbed (39) Enzymes released by the pancreas become active in the duodenum for protein digestion Multiple enzymes are needed to break down proteins into amino acids Fats are emulsified by bile released from storage in gall bladder Carbs are initially broken down in the mouth by saliva Virtually all nutrient absorption takes place in the small intestine

Electrolyte absorption (40) Electrolytes are reclaimed in the large intestine – along with any remaining water and vitamins concentration gradient allows diffusion back into mucosal cells

Water absorption (41) 95% of water is absorbed in the small intestines by osmosis water uptake is coupled with solute uptake and as water moves into mucosal cells substances follow along their concentration gradients