Topic 6.1

Question 1

What are the 2 big plexuses of GI system and their fct?

Answer 1

• Myenteric (Auerbach) : for motility

- Submucosal (Meissner) : for digestion

Question 2

On top of Ach and NE, what are some molecules that can regulate GI? (3 examples per term)

Answer 2

• Non peptides : 5HT3, ATP, NO

- Peptides : VIP, substance P, opioids

Question 3

What are the 2 main effects of the sympathetic system on GI?

Answer 3

1 - circulatory : causes contraction of vessels

2 - NE can close / contract the sphincters and limit bowel movement

Question 4

What is the gastroenteric reflex?

Answer 4

enhanced peristalsis

Question 5

What mediates the gastroenteric reflex?

Answer 5

Myenteric plexus and gastrin

Question 6

What is the gastroileal reflex?

Answer 6

stimulation of peristalsis in the ileum + opening of ileocecal sphincter after a meal

Question 7

What facilitates the gastroileal reflex?

Answer 7

Gastrin

Question 8

What are the gastrocolic and duodenocolic reflexes?

Answer 8

Distention of the stomach / duodenum stimulates evacuation of the colon. Blunted in adults

Question 9

What transmits the gastrocolic / duodenocolic reflex?

Answer 9

The ANS

Question 10

What is the enterogastric reflex?

Answer 10

distention and irritation of the small intestine results in suppression of secretion and motor activity in the stomach

Question 11

What mediates the enterogastric reflex?

Answer 11

the ENS and ANS

Question 12

What is the colonocolic reflex?

Answer 12

Propels stool caudally by proximal muscle constriction + distal muscle distention

Question 13

What mediates the colonocolic reflex?

Answer 13

the myenteric plexus

Question 14

What are the rectocolic (defecation) reflexes?

Answer 14

• Intrinsic reflex mediated my myenteric plexus

- Parasympathetic defecation reflex mediated by the pelvic nerve

Question 15

3 types of neurons of ENS?

Answer 15

• Afferent neuron
• Interneuron
• Efferent neuron

Question 16

What type of stimuli can activate the ENS?

Answer 16

• mechanical / chemical

- local / external (smell)

Question 17

What is paraneoplastic syndrome?

Answer 17

misproduction of regulatory molecules due to cancer / tumour (called neoplasm)

Question 18

7 molecules involved in endocrine regulation

Answer 18

• CCK (cholescystokinin)
• Gastrin
• Secretin
• GIP (gastric inhibitory peptide)
  (- Ghrelin)
  (- Aldosterone)
  (- Calcitriol)

Question 19

What produces CCK?

Answer 19

The i-cells in the duodenum

Question 20

What is CCK useful for? (3)

Answer 20

• increases pancreatic juice secretion (enzymes + bicarbonate)
• decrease gastric emptying
• contraction of gallbladder

Question 21

What produces Gastrin?

Answer 21

G cells of stomach and small intestine

Question 22

What is gastrin useful for? (2)

Answer 22

• Gastric acid secretion

- Growth of gastric mucosa

Question 23

What is secretin useful for?

Answer 23

• pancreatic juice secretion based on acid content of the duodenum

Question 24

What produces secretin?

Answer 24

S-cells

Question 25

What produces GIP?

Answer 25

K-cells of the intestines

Question 26

What are the roles of GIP?

Answer 26

- increase of insulin secretion | - inhibition of gastric emptying (gastric content released in intestines)

Question 27

What molecules is GIP a part of?

Answer 27

Incretins

Question 28

What produces ghrelin?

Answer 28

P/D1 cells of the stomach, when it's empty to signal hunger

Question 29

What is the role of aldosterone in GI?

Answer 29

regulation of epithelial Na, K absorption in colon

Question 30

What is the role of calcitriol in GI?

Answer 30

enhances intake of Ca2+ from the lumen

Question 31

What are the 3 paracrine molecules involved in paracrine regulation of GI?

Answer 31

- Serotonin - Histamine - Somatostatin

Question 32

What releases serotonin?

Answer 32

enterochromaffin cells

Question 33

When is serotonin released by EC cells?

Answer 33

when there is mechanical stretch of the GI wall

Question 34

What is the role of histamine in GI?

Answer 34

increases gastric acid secretion

Question 35

What releases histamine in GI? (2)

Answer 35

- ECL cells (enterochromaffin like cells) | - mast cells

Question 36

What is the effect of somatostatin on GI?

Answer 36

- General inhibitory effect : decrease gastric acid secretion, decrease nutrient absorption

Question 37

What releases somatostatin?

Answer 37

the D cells