Motility of the gut

Question 1

Segmental contractions =

Answer 1

non-propulsive movement of luminal contents to mix chyme + secretions

Question 2

Peristaltic contractions =

Answer 2

propulsion of chyme and it’s digested products in the caudal direction eliminate non-digested/absorbed material

Question 3

The small intestine has which types of motility in the absorptive/fed state?

Answer 3

segmentation and peristalsis

Question 4

The small intestine has which type of motility in the fasting state?

Answer 4

migrating motor complex (MMC)

Question 5

What are migrating motor complexes (MMCs), when and why do they occur?

Answer 5

Synchronized rhythmic contractionn of the small intestine every 90-120 mins of being quiescient.
Usually go from stomach -distal ileum.
Purpose it to move particles >2mm from stomach to duodenum.

Question 6

The hormone associated with MMCs

Answer 6

motilin (secreted by duodenum just before peak of activity)

Question 7

Ileogastric reflex =

Answer 7

ileal distension leads to decreased gastric motility (ENS mediated)

Question 8

Gastroileal reflex =

Answer 8

increased gastric activity causes increased ileal motility and increased movement of chyme through the ileoceacal valve (ENS mediated)

Question 9

Which vitamins are synthesised by bacteria in the colon

Answer 9

B K

Question 10

Functions of the colon

Answer 10

Proximal colon: 
Absorbs large quantity of fluid and ions converting liquid > solid matter
Absorbs SCFA 
Environment for beneficial bacteria 
Secretes ions 

Distal colon:
Storage/resevoir
Regulates feaces release

Question 11

Colonic rhythmic phasic contractions (RPCs) =

Answer 11

short duration and long duration contractions

highly disorganised in space & amplitude so good at turning over fecal matter with slow rate of propulsion

Question 12

Giant migrating contractions (GMCs) in the colon =

Answer 12

• large-amplitude lumen- occluding contractions that propagate very rapidly to produce mass movements.
• occur 2-10 times a day
• occur in fasting and fed state

Question 13

The autonomic NS (SNS and PSNS) controls motility of the colon.
Which parasympathetic nerve innervates the cecum, ascending and transverse colon?

Answer 13

branches of the vagus

• innervate RPCs in the proximal colon

Question 14

The autonomic NS (SNS and PSNS) controls motility of the colon.
Which parasympathetic nerves innervate the descending, sigmoid colon, rectum and anal canal?

Answer 14

pelvic nerves from the sacral spinal cord (“sacral outflow”)

-innervate GMCs in the distal colon

Question 15

Describe the reflexes involved in defecation

Answer 15

1. faeces enter rectum - distension
2. Intrinsic defecation reflex by myenteric plexus > peristalsis & internal anal sphincter relaxes (weak)
3. Reinforced by the parasympathetic defecation reflex (sacral outflow) > peristaltic waves amplified and internal anal sphincter relaxes
4. Defecation can be inhibited by conscious control over external anal sphincter

Question 16

Smooth muscle contraction of the small intestine is controlled by what?

Answer 16

Contraction - Ach, motilin, somatostatic, myogenic stretch reflex
Relaxation - Vasoactive intestinal peptide (VIP)

ENS modulated by ANS