Control of smooth muscle in the GI tract

Question 1

What are the types of muscle in the GIT

Answer 1

Smooth (involuntary) muscle in most regions

Skeletal (voluntary) muscle in the pharynx top third of the oesophagus, external anal sphincter

Question 2

What are the functions of the GIT

Answer 2

digestion
absorption
secretion
motility

Question 3

What are the two types of smooth muscle?

Answer 3

Phasic - rapid relaxation and contraction of the muscle

Tonic - muscle remains contracted or relaxed for a long duration of time

Question 4

what are the interstitial cells of CAJAL (ICC)

Answer 4

Pacemaker cells which have a spontaneous oscillating membrane potential. These cells are electrically coupled to the smooth muscle cells through gap junctions.

Question 5

What can cause stimulation of electrical activity of smooth muscles in the GIT? (depolarisation)

Answer 5

stretch
acetylcholine
parasympathetics

Initiates smooth muscle contraction

Question 6

What can cause hyperpolarisation of smooth muscles in the GIT?

Answer 6

Noradrenaline
sympathetics

Initiates smooth muscle relaxation

Question 7

What is the role of Ca2+ ions in smooth muscle contraction?

Answer 7

Ca ions bind to calmodulin which activates myosin light chain kinase enzyme when phosphorylates myosin, allowing it to interact with actin and therefore mediates contraction.

Question 8

How does relaxation occur in smooth muscle?

Answer 8

MLCP phosphatase dephosphorylates myosin so it no longer interacts with actin molecules and hence contraction is halted.

Question 9

How is Ca controlled to control contraction?

Answer 9

Ca ions are exchanged by a Na-Ca exchanger of Ca pump, but this eventually would deplete the cell of Ca ions.
Instead Ca ions re-uptake into the sarcoplasmic reticulum

Question 10

How can relaxation of smooth muscle be maintained?

Answer 10

MLCP can itself be phosphorylated meaning that it cannot interact with calmodulin and as such no muscle contraction will be cause

Question 11

What does activation of the myenteric plexus do?

Answer 11

Increases tonic contraction
increases intensity of rhythmic contractions
increases the rate of rhythmic contractions
increases velocity of conduction

Question 12

What does activation of the submucosal plexus do?

Answer 12

Involved primarily with the absorptive function of the GIT

Question 13

What are the different types of movements in the GIT?

Answer 13

A.Propulsive movements: PERISTALSIS

B.Non-propulsive movements: SEGMENTATION

C.Interdigestive: MIGRATING MOTOR COMPLEX (MMC)

Question 14

What sensory receptors are involved in the GIT?

Answer 14

Enteric sensory neurones

Question 15

What are the roles of the para/symp NS in motility of the GIT?

Answer 15

Sympathetic inhibits motility

Parasympathetic initiates motility

Question 16

What type of reflexes are involved in the gut wall?

Answer 16

Ileogastric
gastrocolic
enterogastric

Question 17

What is the Gastro colic reflex?

Answer 17

sensory distension initiating a reflex of contractions in the large intestine allowing more room for new food in the colon.

Question 18

What is the intestine intestinal reflex?

Answer 18

(inhibitory reflex)

prevents excess chyme being secreted into the ileum when distention hasn’t been fully completed

Question 19

What is Hirschsprung disease?

Answer 19

Congenital lack of neuronal ganglionic cells in the ENS leading to a lack of motility and therefore can cause MEGAcolon

Question 20

What is Chagas disease?

Answer 20

infectious disease of a parasitic nature, resulting in the significant reduction in the number of ganglionic cells in the ENS

Question 21

What is Achalasia?

Answer 21

a condition in which the muscles of the lower part of the oesophagus fail to relax, preventing food from passing into the stomach caused by a dramatic reduction in the number of neuronal cells in the lower oesophageal segment.

Question 22

What are some gastric functions of the stomach?

Answer 22

gastric emptying/release
Food storage
gastric motility and mixing

Question 23

How is the stomach adapted for storage function?

Answer 23

Can be highly folded and upon filling the folds flatten out allowing an increase in volume.
Once the stomach folds extend fully (via the vago-vagal reflex) then the intraluminal pressure increases and it becomes harder to eat.

Question 24

what are the phases of gastric motility in the stomach?

Answer 24

Propulsion - rapid flow of liquids and suspended small particles are pushed down towards the pylorus.
Grinding - the emptying of liquids and small particles but larger particles are retained in the bolus and are subject to grinding.
Retropulsion - this is where large particles are cleared in the terminal antrum

Question 25

What is the function of the pylorus?

Answer 25

allows carful regulated emptying of gastric contents | prevents regurgitation of duodenal contents

Question 26

What are the phases of gastric emptying?

Answer 26

– Cephalic - approach of food or food in the mouth – Gastric - food in the stomach – Intestinal - food in duodenum, ileum or colon

Question 27

What occurs during the cephalic phase of gastric emptying?

Answer 27

An inhibitory phase - Inhibitory nerve fibres in the vagus nerve Results in relaxation of stomach enabling it to store large volumes

Question 28

What occurs during the gastric phase of gastric emptying?

Answer 28

Is an excitatory phase in which the stomach empties at rate proportional to the volume in it.

Question 29

What occurs during the intestinal phase of gastric emptying?

Answer 29

It is (mainly) an inhibitory phase, through which the duodenum adapts the “work-load” as a function of the state of the digestive process.

Question 30

what is the predominant excitatory neurotransmitter for smooth muscle control?

Answer 30

ACh

Question 31

What is the predominant inhibitory neurotransmitter for smooth muscle control?

Answer 31

VIP and NO

Question 32

Which fibre inhibits and stimulates motility by controlling the resting membrane potential?

Answer 32

Stimulation of membrane potential by Sympathetic fibres inhibit motility Stimulation of membrane potential by parasympathetic fibres increases motility.

Question 33

What are the symptoms of Hirschsprung disease?

Answer 33

Vomiting constipation distension of abdomen Intestinal obstruction

Question 34

What patient evaluation takes place to diagnose Hirschsprung's disease?

Answer 34

plain abdominal radiography Rectal manometry Biopsy

Question 35

What is the treatment for Hirschsprung's Disease?

Answer 35

Removal of Aganglionic segment and subsequent anastomosis

Question 36

What is the clinical presentation of Achalasia?

Answer 36

``` Solid Dysphagia (difficulty swallowing) Chest pain Regurgitation Pyrosis Weight loss Nocturnal cough and recurrent aspiration. ```

Question 37

What is the diagnosis of Achalasia?

Answer 37

Plain film Barium esophagogram Endoscopy Oesophagal manometry

Question 38

What is the treatment for Achalasia?

Answer 38

Nitrates and Calcium Channel Blockers Botulinum toxic preventing ACh release at NMJ Pneumatic dilation Surgical myotomy.

Question 39

What causes the emptying of the stomach during the gastric phase of

Answer 39

Myogenic reflex: stretching smooth muscle causes reflex contraction Activation of pressure receptors which send impulses in local nerve plexi and in the vagus nerve Gastrin released in response to peptides etc

Question 40

What controls the intestinal phase of gastric emptying?

Answer 40

This phase is mainly controlled through hormonal and paracrine mechanisms, activated by duodenal chemoreception. There are also some motor reflexes such as ileogastric reflex delaying gastric emptying

Question 41

What are the intestinal mechanisms controlled by hormonal and paracrine mechanisms?

Answer 41

Low pH - activates secretion of Secretin High fats/lipids - increase secretion of CCK High levels of amino acids - increase secretion of Gastrin High levels of carbohydrates - increased secretion of GIP

Question 42

What is the significance of The intestinal phase of gastric emptying being inhibitory?

Answer 42

delays gastric emptying increasing the time taken for the GI tract to empty and thus allow more time for digestion.