12 motility in the GI tract

Question 1

What are the 3 functions of motor activity in the GI tract?

Answer 1

segmental contraction for mixing
peristaltic contractions
reservoir formation (sphincters)

Question 2

What is MMC?

Answer 2

Migratory Motor Complex, pattern of electrochemical activity in GI smooth muscle for moving undigested material in the fasted state

Question 3

What are the 4 phases of MMC?

Answer 3

prolonged quiescence (90-120 minutes)
increased AP + contractions
Peak activity
declining activity

Question 4

What are the 3 main functions of MMC?

Answer 4

morve particles of greater than 2mm diameter
clear small intestine of residual content
prevent colic bacteria from migrating to the ileum

Question 5

What is FMP?

Answer 5

fed motor pattern, it halts MMC during feeding

Question 6

What regulates FMP?

Answer 6

ENS

Hormones like motilin, released just before stage 3 MMC

Question 7

What hormones initiate smooth muscle contraction?

Answer 7

motilin and somatostatin

Question 8

What initiates smooth muscle relaxation?

Answer 8

vasoactive intestinal peptide

Question 9

What are the 2 reflexes of the ileum?

Answer 9

ileogastric motility (ileum distension -> gastric relaxation)
gastroileal reflex (increased gastric activity causes increases ileal activity)

Question 10

What separates the ileum and colon?

Answer 10

ileocaecal sphincter

Question 11

What are teniae coli?

Answer 11

the 3 muscular bands running the length of the colon

Question 12

What are the haustra?

Answer 12

contractions up the colon forming pouches

Question 13

What is the function of the proximal colon?

Answer 13

absorption and bacterial fermentation

Question 14

What is the function of the distal colon?

Answer 14

reservoir / storage

Question 15

What are the 2 phases of colon motility?

Answer 15

colonic rhythmic phasic contractions

giant migrating contractions

Question 16

Why do we have colonic rhythmic phasic contracitons?

Answer 16

as contents move up the ascending colon, they become more solid as water is absorbed, so we hence have short and long duration contractions here

Question 17

How does distension activate colon motility?

Answer 17

indigestable food passes quickly, activating pressure receptors, stimulating contraction via the myenteric plexus

Question 18

What food prevent contraction?

Answer 18

bran
fruit
veg

Question 19

Name 4 classifications of laxatives

Answer 19

stimulant laxatives
saline laxatives
emollient laxatives
bulk-forming laxatives

Question 20

How do stimulant laxatives work?

name one household product containing a simtulatnt laxative

Answer 20

increase motility through chemoreceptor activation and myenteric plexus
castor oil has ricinoleic acid, inhibiting Na+ transport

Question 21

How do saline laxatives work?

give an example

Answer 21

osmosis

Magnesium sulphate

Question 22

How do emollient laxatives work?

Answer 22

soften faeces

Question 23

What are bulk-forming laxatives normally made from?

Answer 23

dietary fibre (bran or methylcellulose)

Question 24

How does the Parasympathetic nervous system stimulate colon motility?

Answer 24

Vagus nerve - RPC’s in cecum, ascending colon, transverse colon
Pelvic nerves from sacral spinal, stimulates GMC (other distal bits)

Question 25

What is the intrinsic defecation reflex stimulated by and what mediates it?

Answer 25

rectum distension

myenteric plexus

Question 26

what is the function of the parasympathetic defecation reflex?

Answer 26

relaxation of internal anal sphincter not really enough to force out shit so it helps