Small and Large Intestine Motility

Question 1

two major functions of duodenum that enable high digestion and absorption

Answer 1

segmentation

peristalsis

Question 2

segmentation

Answer 2

muscle contractions generate by enteric nerves –> appear as rings that narrow the lumen

occur at sites of distension…so that the distending bolus is roughly cut in half

process is repeated over and over again –> ‘dance of the intestines’

maximizing mixing of chyme with enzymes and bile for both digestion and absorption of valuable substances in chyme

Question 3

small intestine perstalsis

Answer 3

designed to move contents into colon

also puts contents in contact with other parts of small intestine that may have specialized absorptive function

Question 4

peristalsis rate of each SI segment

Answer 4

duodenum = max 12/min

jejunum = 10

ileum = 8

each determined by pacesetter muscles

Question 5

ileo-colic reflex

Answer 5

when contents reach end of small bowel and distend the ileum end….neural ileo-colic reflex initiated

results in relaxation of the ileocecal valve allowing contents to flow into the cecum

as cecum distends –> ileo-colic reflex is inhibited … important to keep bacterial gradient between large and small bowel

Question 6

migrating motor complex (MMM)

Answer 6

motor function of GI tract remains active even in fasting periods

begins 2 hours after meal in the gastric antrum

peristaltic wave sweeps from the antrum –> entire SI and ends at ileoceccal valve 2 hours later

then repeats

important for ‘housekeeping patterns’ - removes particles larger than 2mm from stomach and clears residual chyme from the small bowel to prevent bacterial overgrowth in SI

eating abolishes the MMM wherever in the cycle it is (probably due to the release of gastrin and CCK)

Question 7

anus is guarded by what two contracted muscles

Answer 7

SmM internal anal sphincter

SkM external anal sphincter

Question 8

functions of the large colon account for

Answer 8

the changes in fluidity of the feces

1. absorption of water and electrolytes…around 90% leaving 200cc for softening of stool
2. elimination of undigestible solid residue

Question 9

2 types of large bowel motor movements

Answer 9

1. haustration

2. mass movements

Question 10

haustration in large bowel

Answer 10

like segmentation in SI

segmental contractions designed to bring feces close contact with the colonic epithelium for water and salt absorption

Question 11

mass movements in large bowel

Answer 11

like peristaltic movements in small intestine

moves feces distally for preparation of elimination

Question 12

defecation reflex

Answer 12

once sufficient amounts enter the rectum and rectal distension occurs

release of NO for relaxation of the SmM internal anal sphincter

allows feces and gas to enter the anal canal…where sensory signals in the region distinguish the nature of the material

Question 13

if timing is inconvenient to shit

Answer 13

active contraction by neural release of Ach of the SkM external anal sphincter (and puborectalis muscle) raises its pressure to no materal passes to the outside world

Question 14

if you want to shit…

Answer 14

active relaxation of the external anal sphincter by the inhibition of Ach release –> defecation

Question 15

under conditions when you need to shit but don’t want to…rectal discomfort is overcome by

Answer 15

accomodation of feces residing in the rectum by having the rectal muscles undergo NO mediated receptive relaxation (same mechanism found in the stomach fundus)

reduced rectal pressure in turn allows the internal anal sphincter to again resume the contracted state adn removes the need for voluntary contraction of the external anal sphincter and puborectalis

Question 16

puborectalis muscle

Answer 16

acts as a rein on the rectum with contraction producing a sharp angle that impedes feces entering teh anal canal and relaxation straightening the rectum allowing feces to enter the anal canal

Question 17

gastroscopic reflex

Answer 17

food entering the stomach stimulates a neural signal to the colon to produce a mass movement

which forces material into the rectum and when sufficient rectal distension occurs –> defecation relfex occurs

Question 18

gastrolienal reflex

Answer 18

food entering the stomach signals the distal small bowel to empty remaining chyme into the right colon