Physio- Large Intestine

Question 1

List the three types of movement of the large intestine.

Answer 1

1. Nonpropulsive segmentation - contraction of circular muscles and contributes mixing to the colonic contents
2. Peristalsis - propels colonic contents in the distal direction
3. Mass movement - a strong wave contraction that drives colonic contents into the rectum. (Gastrocolic reflex)

Question 2

Explain the two types of anal sphincters.

Answer 2

1) the external anal sphincter contains striated muscles and are voluntarily controlled. They received somatic innervation from the spinal cord.

2) the internal anal sphincter contains smooth muscle and are involuntarily controlled. They receive automatic innervation from spinal cord.

Question 3

Explain the defecation reflex.

Answer 3

Fecal material stimulates stretch receptors:
1) the stretch receptors sends a signal to the sensory fibers of the pelvic nerve and to the spinal cord.
2) the spinal motor neurons send a signal to the motor fibers of the pelvic nerve back to the rectum.
3) stimulation of contractions of the longitudinal muscles in the anal wall and relaxes the internal anal sphincter.
4) defecation is assisted by Valsalva maneuver.
5) the maneuver increase intra-abdominal pressure causing compression on the colon and rectum resulting in defecation.

Question 4

State the functions of microflora in large intestine.

Answer 4

Fermentation of non absorbed nutrients
Metabolism of bilirubin
Production of vitamins

Question 5

Describe the functions of bacteria (intestinal microflora) in the fermentation of the large intestine.

Answer 5

1. Bacteria digest the remaining carbohydrates and converts them into gases such as CO2, hydrogen and methane. (Cases flatus-pomp)
2. Bacteria convert remaining protein into amino acids and convert them into substances indole, skatole and hydrogen sulfide. (Causes odor in feces)
3. Bacteria produces B vitamins and vitamin K.

Question 6

Discuss the absorption of Na+ in the large intestine.

Answer 6

1. Na+-H+ exchanger operates the proximal colon
2. Na+ channel operates distal colon.

Question 7

Discuss the absorption of Cl- in the large intestine.

Answer 7

1. Paracellular absorption - distal colon
2. Transcellular absorption via Cl-/HCO3- exchanger - proximal colon

Question 8

Discuss the absorption of K+ in the large intestine.

Answer 8

1) K is absorbed via the transcellular pathway in the distal colon.
2) K+ is absorbed in the luminal membrane via secondary active transport coupled with H+-K+ pump.