GI Motility

Question 1

What three functions does motor activity of the GI tract allow?

Answer 1

1. Segmented contractions which allow for the churning and mixing of food with no propulsive movements.
2. Peristaltic contractions - Propagated movement of food in the caudal direction. This eliminates non-digested and nonabsorbed food.
3. Allows for hollow organs such as the stomach and the intestines to act as reservoirs with the help of the sphincters.

Question 2

What two muscle type are important for the motor activities in the GI tract?

Answer 2

Tonic and Phasic muscle

Question 3

Structure of the small intestine?

Answer 3

9ft long extending from the stomach to the colon. Has enterocytes which line the villi and stem cells present in the crypts.

Question 4

Where does majority of absorption occur?

Answer 4

Within the small intestines

Question 5

Functions of the small intestines?

Answer 5

Digestion, Absorption, Secretion and motility.

Question 6

What are the functions of motility in the small intestines?

Answer 6

1. Mixes chyme with secretion from the pancreas, liver and intestines.
2. Propulsion - Moves food to correct site of absorption
3. Releases chyme into the colon

Question 7

What types of motility are experienced in the absorptive state?

Answer 7

Segmentation - Rings of circular muscle at intervals contract then relax followed by the rings of adjacent circular muscle with the overall result of mixing.
Peristalsis - Sequential contraction of rings circular muscle followed by relaxation. main result is to propel chyme along.

Question 8

During the fasted state, is there still motility?

Answer 8

Yes, there is the migrating motor complex

Question 9

What is the migrating motor complex (MMC)

Answer 9

It is a distinct pattern of electromechanical activity in the GI tract that is undergone during the fasted state.

Question 10

What it the purpose of MMC?

Answer 10

It is to eliminate any undigested materials from the stomach.

Question 11

What are the phases of MMC

Answer 11

1. Prolonged period of quiescence;
2. Increased frequency of action potentials and smooth muscle contractility.
3. Few minutes of peak electrical and mechanical activity, and;
4. Declining activity which merges with Phase 1

Question 12

What stops MMC?

Answer 12

Feeding as it initiates segmentational and peristaltic contractions

Question 13

what regulates the transition from MMC to fedstate?

Answer 13

The enteric nervous system, Humoral factors and extrinsic innervations

Question 14

What hormone is the major determinant of MMC?

Answer 14

Motilin
release just before phase 3.
Synthesised in duodenal mucosa.

Question 15

What controls smooth muscle contractility?

Answer 15

ACH, somatostatin and motilin - contraction
Vasoactive intestinal peptide - Relaxation.
Stretch cause contraction mediated by ca2+ influx
ENS mediated by ANS.

Question 16

what is the ileogastric reflex?

Answer 16

inhibition of gastric motility due to distension of the ileum.

Question 17

What is the Gastroileal reflex?

Answer 17

It is increased ileal motility caused by the increased gastric activity. leading to the movement of chyme through the ileoceacal valve.

Question 18

What is the ileoceacal valve?

Answer 18

Sphincter that separates small intestine from large intestine.

Question 19

Functions of the colon?

Answer 19

Absorbs large quantities of fluid and electrolytes, forming solids.
Absorbs SCFAs
Storage
Regulates release of faecal matter
Provides ideal environment for vitamin synthesis
Secretes mucous and ions.

Question 20

What are the two distinct regions of the colon

Answer 20

Proximal colon and distal colon

Question 21

What are the two major types of colonic motility?

Answer 21

Rhythmic phasic contractions.

Giant migrating contractions

Question 22

What diseases are caused by a western diet?

Answer 22

Constipation, Diverticular disease 
haemorrhoids 
polyps 
cancer of the colon 
irritable colon 
ulcerative colitis

Question 23

How do stimulant laxatives work?

Answer 23

By increasing motility through the activation of chemoreceptors and the myenteric plexus.

Question 24

How do saline laxatives work?

Answer 24

By drawing water into the bowel via osmosis due to high concentration of osmotic substances

Question 25

How do emollient laxatives?

Answer 25

By increasing intestinal fluid

Question 26

How do bulk forming laxative work?

Answer 26

These are non-fermentable so they cause swelling due to water absorption which cause distention and motility.

Question 27

How is motility in the colon controlled?

Answer 27

By the autonomic nervous system. Sympathetic activation inhibits colon motility while parasympathetic increases motility.