GI Motility

Question 1

Where is the GI Tract?

Answer 1

Located between the oesophagus and anal canal

Question 2

What is the GI tract primed by?

Answer 2

Pacemaker cells which initiate a spreading basal electrical rhythm
-These pacemaker cells are now known as Interstitial Cells of Cajal

Question 3

How does the GI Tract cause movement of chyme?

Answer 3

When Chyme presses against the membranes, it causes a release of ACh (acetylcholine) and VIP (vasoactive intestinal peptide)

• ACh binds to the smooth muscle cells surrounding the ICC and cause a contraction to the previous section of GI Tract already travelled through
• VIP binds to the ICC and causes a relaxation, increasing the area and pushing the chyme along the tract

Question 4

How do parasympathetic and sympathetic nerve activation affect the GI Tract?

Answer 4

• Parasympathetic Nerve Activation Promotes increased motility
• Sympathetic Nerve Activation:
• Decreases motility directly via beta-adrenoceptors and indirectly by decreasing ACh release via alpha2-adrenoceptors

Question 5

What is GI activity also influenced by?

Answer 5

Locally produced chemicals and hormones

Question 6

What are the stages of gastrointestinal motility?

Answer 6

1) mastication (oropharyngeal phase)

2) deglutition (oesophageal phase)

Question 7

What is an oesophagus?

Answer 7

A hollow tube separated at either by physiological sphincters

Question 8

What creates a sphincter?

Answer 8

A zone of elevated pressure (ZEP) from muscle myogenic tone

Question 9

What is the primary wave of oesophageal perstalsis?

Answer 9

mechanoreceptors in pharynx detect food bolus which initiates peristaltic wave controlled by vagal nerves

• The rate of movement is proportional to the viscosity of the bolus
• Contraction speed is 5cm/sec and whole wave lasts 7-10secs

If food is not projected to stomach, secondary wave of peristalsis is initiated by local vago-vagal reflexes

Question 10

What is the freuency of the spreading basal ecetrical rhythm (BER)?

Answer 10

3-5min

-Not always associated with the peristaltic wave, only when the underlying smooth muscle is at its most excitable

Question 11

What is smooth muscle excitability controlled by?

Answer 11

1) myogenic properties of smooth muscle cells
2) activity of intrinsic nerves
3) activity of extrinsic nerves
4) hormones or locally produced chemicals

Question 12

What occurs on a full stomach?

Answer 12

• 1st hour, peristaltic waves are weak (ZEP is closed)

- After 1st hour, peristaltic waves are more powerful

Question 13

How is the Control of Gastric Motility achieved?

Answer 13

Neural Control
- Vagal relaxatory fibres induce relaxation in corpus and fundus which are mediated by VIP
- Sympathetic (NA) stimulation inhibits via inhibiton parasympathetic ganglion transmission
- Vagal fibres releasing ACh stimulate gastric motility
Hormonal Control
- Stimulatory hormones are gastrin & motilin
- Inhibitory hormones are gastrin, secretin and CCK

Question 14

What factors affect the rate at which contents pass into the duodenum?

Answer 14

• Gastric Motility
• Meal Composition
• Meal Volume
• Fragment Size
• Osmolarity
• Acid
• Fat

Question 15

How does Small intestine motility work?

Answer 15

Intestinal contents are mixed with the secretions of mucosal cells and with the pancreatic juice and bile

Question 16

What are the two types of muscular contractions in the small intestine?

Answer 16

• Segmenting contractions

- Peristaltic contractions

Question 17

What are segmenting contractions?

Answer 17

Only occur in circular muscle and moves chyme both directions to increase exposure to mucosal surface

Question 18

What are peristaltic contractions?

Answer 18

• more longitudinal muscle
• normally over short distances
• after meals

-occasional propulsive movement propogating over long distances called migrating motility complex (MMC)

Question 19

How is small intestine motility controlled?

Answer 19

1) Myogenic mechanisms
2) Myenteric plexus (local regulation)
3) Extrinsic nerves
4) Local chemicals

Question 20

How does large intestine motility take place?

Answer 20

Principle functions of large intestine are to reabsorb water and store faeces

• movement mostly slow and non-propulsive (similar to segmentation contractions but more infrequent 2/hr)
• 3 to 4 times per day there are powerful contractions that drives contents to distal portion of large intestine prior to defecation

Question 21

How long does it take food to reach the terminal ileum?

Answer 21

12 hours

Question 22

What is defecation?

Answer 22

• rectum usually empty

- arrival of faecal material induces desire to defaecate dues to peristaltic waves in colon