GI Motility

Question 1

Which parts of the GI tract have voluntary skeletal muscle rather than involuntary smooth muscle?

Answer 1

Proximal third of the stomach, upper oesophageal sphincter and external anal sphincter

Question 2

Describe what is meant by the slow wave potential of the GI tract

Answer 2

These are not action potentials but oscillating depolarisation and repolarisation of the membrane potential of smooth muscle cells. The depolarisation stage brings the smooth muscle closer to the threshold and if an action potential occurs at the top of these slow waves the cyclical contraction of the GI tract will occur

Question 3

What is the intrinsic rate of the slow waves in the stomach?

Answer 3

3 waves per minute

Question 4

What is the intrinsic rate of the slow waves in the duodenum?

Answer 4

12 waves per minute

Question 5

Which cells are considered the pacemaker cells of the GI tract due to their role in controlling the slow wave mechanism?

Answer 5

Interstitial cells of Cajal

Question 6

The intrinsic rate of the contractions of the GI tract doesn’t change but the strength of contraction can be increased or decreased. True or false?

Answer 6

True

Question 7

Describe the mechanism of swallowing?

Answer 7

The upper oesophageal sphincter open which is mediated by the swallowing reflex. The sphincter closes when the food bolus enters the oesophagus. The swallowing reflex results in a peristaltic wave which pushes the bolus towards the stomach. The vagus nerve mediates opening of the lower oesophageal sphincter and at the same time to topmost part of the stomach relaxes to allow the bolus to flow into the stomach

Question 8

What factors will increase the frequency and force of contractions in the stomach?

Answer 8

Parasympathetic innervation
Motillin
Gastrin

Question 9

What factors will decrease the frequency and force of contractions in the stomach?

Answer 9

Sympathetic stimulation
Secretin
GIP

Question 10

What is the migrating myoelectric complex?

Answer 10

This is a contraction which sweeps the length of the stoma h every 90mins in the interprandial state in order to clear the stomach of any residue. This is mediated by motilin

Question 11

Where is motilin synthesised?

Answer 11

M cells in the small bowel

Question 12

What is the affect of erthromycin on motilin?

Answer 12

It is a motilin antagonist

Question 13

What is the emptying rate from the stomach for inert liquids?

Answer 13

20minutes

Question 14

How long can it take solids to empty from the stomach?

Answer 14

3-4 hours

Question 15

Fat and hydrogen ions in the duodenal lumen will inhibit gastric emptying. How is this achieved?

Answer 15

Fat stimulates cholecystokinin which increases contraction of the pyloric sphincter
The effect if hydrogen ions is mediated by the enteric nervous system

Question 16

If the small intestine transports solids and liquids at the same rate why are liquids the first to reach the caecum?

Answer 16

Because liquids are released earlier from the stomach and into the duodenum than solids

Question 17

Describe the segmentation contractions of the small intestine

Answer 17

A section of the small intestine contraction and splits the chyme sending some forward and some backwards. It then relaxes which allows the bolus of chyme to merge back together. This action severs to mix the chyme

Question 18

What is the name of the contractions of the large intestine which move food towards the caecum?

Answer 18

Mass movements

Question 19

Explain the control of continence and defecation.

Answer 19

As the rectum fills with farces the smooth muscle wall of the rectum and internal anal sphincter relaxes in the recrosphincteric reflex. However, defecation does not occur because the external anal sphincter is still tonically contracted. When this sphincter is voluntarily relaxed, the smooth muscle of the rectum contracts to create pressure that forces faeces through the anal canal

Question 20

Describe what a normal high resolution mannometry trace of a person swallowing would look like

Answer 20

Here areas of red shiw high pressure and blue shows low pressure. First, the upper oesophageal sphincter is relaxed (as seen by a break in the solid green line to blue which is the to ically contracted sphincter), a wave kf red and yellow peristaltic wave follows this and the bottom of this wave, contraction of the lower sphincter ceases to allow food to enter the stomach

Question 21

Describe how achalasia leads to difficulties swallowing

Answer 21

Here there is no peristaltic contraction due to nerve damage and the lower oesophageal sphincter fails to relax properly. This makes it difficult to eat and patients often have to take large amounts of water to eat a meal and will regurgitate

Question 22

How can achalsia be treated?

Answer 22

A balloon can be used to decrease the pressure in the lower oesophageal sphincter
Laprascopic surgery can also be used ti lower oressure in the lower oesophageal sphincter

Question 23

How does scleroderma lead to severe oesophagitis and excessive reflux?

Answer 23

Scleroderma is a condition which effects connective tissues and this results in very weak peristalsis and a very weak lower oesophageal sphincter which results in excessive reflux and oesophagitis

Question 24

What is nut racker oesophagus?

Answer 24

Hypertensive peristalsis of the oesophagus which has no evident therapies and is associated with pain on swallowing

Question 25

What are the main general causes of delayed gastric emptying?

Answer 25

``` Idiopathic Longstanding diabetes Macro vascular disease Drug use particularly opiates Post viral ```

Question 26

How can delayed gastric emptying treated?

Answer 26

Small meals eaten frequently - liquid food Treat underlying cause Erythromycin acts as a motilin antagonist Metoclopramide and cisalpride are 5HT4 agonists Dopamine antagonists such as dimperidone can be used Botox can be injected into the pyloric sphincter Gastric electrical stimulation via an enterra device

Question 27

Acute post operative ileus leads to constipation in the absence if mechanical obstruction. How long does this last?

Answer 27

0-24 hours if it occurs in the small intestine 24-48 hours if it occurs in the stomach 48-72 hours if it occurs in the large intestine

Question 28

List the risk factors for acute post operative ileus

Answer 28

Open surgery Prolonged abdominal or pelvic surgery Delayed enteral nutrition Peri-operative complications or opiate analgesia

Question 29

Caecal perforations can occur due to acute colonic pseudo obstruction. How is this caused?

Answer 29

Large bowel parasympathetic dysfunction commonly after cardiothoracic or spinal surgery

Question 30

What are some of the causes of chronic intestinal pseudoobstruction?

Answer 30

Myopathic - Scleroderma or amyloidosis Neuropathic - parkinsons Endocrine - diabetes mellitus, severe hypothyroidism Drugs such as phenothiazines

Question 31

How can colonic transit be investigated?

Answer 31

Serial x rays with radioopaque markers

Question 32

How does the drug loperamide work to treat diarrhoea?

Answer 32

It stimulates an opiate receptor to decrease tone and activity of the myenteric nerve plexus

Question 33

How does prucalopride work as a laxative?

Answer 33

It stimulates the 5HT4 receptor to increase colonic motility

Question 34

How does linaclotide work as a treatment for IBS constipation?

Answer 34

Increases the secretion of chloride and bicarbonate ions into the lumen ti increase intestinal fluid and thus speed up colonic transit

Question 35

What are the main general causes of incontinence.?

Answer 35

Damage to pudendal nerve Muscle damage of external anal sphincter Excessive rectal distension

Question 36

What is hirschrungs disease?

Answer 36

A failure of migration of neural crest cells to the distal colon and results in the affected segment if the colon being aganglionic

Question 37

How is hirschrungs disease managed?

Answer 37

Surgical resection of the affected colon

Question 38

Approximately how often to haustral contractions occur?

Answer 38

Every thirty minutes

Question 39

Explain how the location of hasutra changes with contraction of the large intestine?

Answer 39

The relaxed segment which has formed a sac slowly contracts whilst a previously contracted segment simultaneously relaxes to form a new sac - thus the location of the haustra changes

Question 40

What is the purpose of haustral contractions?

Answer 40

To mix the colonic contents and expose them to the colonic mucosa to aid absorption

Question 41

How often to mass movements of the large intestine occur?

Answer 41

3-4 times a day

Question 42

Which reflex triggers mass movements in 5e large intestine?

Answer 42

Gastrocolic reflex

Question 43

Describe the defecation reflex

Answer 43

The movement of faces into the rectum distends the rectum causes stretch receptors to initiate the defecation reflex. This reflex causes relaxation of the smooth muscle internal anal sphincter and contraction of the rectum and sigmoid colon walls. Defecation will not occur however until the voluntarily controlled skeletal muscle of the external anal sphincter is relaxed.

Question 44

What happens if, following the initiation of the defecation reflex, the urge to defecate is not followed by relaxation of the external anal sphincter?

Answer 44

The distended rectal wall will gradually relax and the urge to defecate will subside. This lasts until the next mass movements pushes more faces into the rectum, distends the rectum further and again initiates the defecation reflex