023 Physiology of the GI tract: Motility

Question 1

Which cells generate the slow wave rhythm?

Answer 1

Cells of Cajal

Question 2

Where is slow wave frequency highest?

Answer 2

In duodenum > Ileum > Colon > Stomach

Question 3

What does the propagation of slow waves generate?

Answer 3

Segmental and peristaltic contractions

Question 4

Outline the 3 stages of the swallowing reflex

Answer 4

1. Oral
2. Pharyngeal
3. Oesophageal

Question 5

What is achalasia? What are the symptoms?

Answer 5

The failure of lower oesophageal sphincter to relax. This causes difficulty in swallowing, food sticking on the way down, solids worse than liquids

Question 6

How is food moved down the oesophagus?

Answer 6

Gravity and peristaltic waves

Question 7

Where is the swallowing center in the brain?

Answer 7

Medulla

Question 8

When do hunger pangs occur?

Answer 8

> 8 hours of the stomach being empty

Question 9

What are hunger pangs?

Answer 9

Rhythmic peristaltis contractions that can last 2-3 minutes

Question 10

What are treatments of achalasia

Answer 10

Physical distention of the lower esophageal sphincter or surgically cutting the sphincter.

Question 11

Which part of the stomach causes regulation of gastric emptying?

Answer 11

Distal motor unit (antrum and pyloric sphincter)

Question 12

What is the effect of cholecystokinin on the stomach?

Answer 12

Inhibition of gastric emptying and decreased stomach motility

Question 13

Which part of the stomach acts as a temporary reservoir?

Answer 13

Fundus and body of the stomach

Question 14

Why is there minimal increase in intragastric pressure?

Answer 14

Because stretching of the muscles in the stomach does not change muscular tone

Question 15

Which part of the stomach is responsible for mixing chyme with gastric secretions and why?

Answer 15

Muscle wall in distal unit induces stronger contractions and forces food in pyloric sphincter. The rapid closure of sphincter causes mixing. This causes retropulsion.

Question 16

What is emesis?

Answer 16

Vomiting

Question 17

Why does hypersalivation occur during vomiting reflex?

Answer 17

Protection of epithelium from the acid in the vomit.

Question 18

Why does reverse peristalsis occurs in the vomiting reflex?

Answer 18

Stomach and pyloric sphincter relaxes, causing change in pressure and the reverse peristalsis of chyme back from duodenum.

Question 19

What does the muscularis mucosa do?

Answer 19

When it contracts, it agitates unstirred water layer rich in nutrients, allowing it to get in contact with epithelium for adsorption. This ‘piston like movement’ also allow chylomicrons to move down the lacteal.

Question 20

When does segmentation occurs strongest?

Answer 20

Duodenum

Question 21

What is the purpose of segmentation?

Answer 21

Mixing movements with no net forward movement. It is the contraction of circular smooth muscle that faciliates mixing.

Question 22

Which movement is responsible for the net forward movement of chyme?

Answer 22

Peristalsis at the rate of 1cm/min

Question 23

What are the movements of muscles during peristalsis?

Answer 23

Waves of contraction and relaxation of circular and longitudinal smooth muscle.

Question 24

When does the migrating motor complex occur?

Answer 24

During interdigestive phase; initiated during hunger pangs

Question 25

What does the migrating motor complex do?

Answer 25

Responsible for clearing out undigested products into the colon. It also stops the overgrowth of microorganisms.

Question 26

Which hormone increases the migrating motor complex?

Answer 26

Motilin

Question 27

Which hormone decreases the migrating motor complex?

Answer 27

Gastrin, CCK etc.

Question 28

What is function of the ileal brake reflex?

Answer 28

This prevents unabsorbed nutrients from entering the colon. Slows down movement of GI tract to allow adsorption; maintains gut microbe environemnt.

Question 29

How does the ileal brake reflex work?

Answer 29

Delays gastric emptying, jejunal transit and suppresses hunger

Question 30

Which sphincter is responsible for moving food into the caecum?

Answer 30

Ileocecal sphincter

Question 31

Which movements occur in the colon?

Answer 31

Mixing (haustrations)

Propulsive (peristalsis)

Question 32

What stimulates the defaecation reflex?

Answer 32

Sudden distension of the rectal wall (stretch receptors)

Question 33

Why might a diet high in fibre speed up intestinal motility?

Answer 33

Fibre retains water which increase bulk of contents and stimulates motility

Question 34

Why would prior ingestion of oil or milk reduce neural effects of alcohol?

Answer 34

Alcohol is partly absrobed in stomach but more rapidly absorbed in the SI. Fat reduces gastric emptying (CCK mediated), which delays intestinal uptake of alcohol.

Question 35

What mechanisms minimise changes in wall tension and intraluminal pressure in proximal stomach?

Answer 35

Release of inhibitory transmitters from parasympathetic nerve fibres e.g. VIP, NO.

Question 36

What nerve reflexes are involed in defaecation?

Answer 36

i. somatic nerves - voluntary control of external anal sphincter.
ii. autonomic - stimualtion of stretch receptors in sigmoid colon/rectum results in relaxation of sphincter.

Question 37

What is Hirschsprung disease?

Answer 37

Congenital absence of enteric neurons causing poor mixing and transit. Accumulation causes colonic distension.

Question 38

What are nerve varicosities?

Answer 38

Nerve (swellings) that release transmitters that diffuse into the syncytium.

Question 39

How does the GI smooth muscle act as a syncytium?

Answer 39

Nerve transmitters are rapidly transmitted through the gap junctions.

Question 40

Which nerves stimulate the ileocaecal sphincter?

Answer 40

Myenteric plexus and prevertebral sympathetic ganglia.