4. intestinal hormones and motility

Question 1

What is the main regulatory organ for appetite?

Answer 1

ventromedial nucleus of the hypothalamus

Question 2

What are the different theories of appetite regulation?

Answer 2

• Lipostat - fat deposits and leptin
• Gut peptides - CCK
• Glucostat - glucose/VFAs/AAs
• Thermostat

Question 3

Describe the lipostat hypothesis of appetite regulation

Answer 3

Adipose tissue produces leptin proportionally to amount of fat -> hypothalamus -> decreases food intake and increase energy output

Question 4

Describe the gut peptide hypothesis of appetite regulation

Answer 4

GI hormones e.g., glucagon released in response to food and act on hypothalamus to inhibit food intake
CCK found in brain and is released upon expansion of the stomach
Ghrelin from stomach increases before meals and stimulates appetite at hypothalamus levels by reducing leptin levels

Question 5

Describe the glucostat hypothesis of appetite regulation

Answer 5

High glucose e.g., after meal -> stimulates satiety (fullness) centre in hypothalamus

Question 6

Describe the thermostat hypothesis of appetite regulation

Answer 6

Low body temp stimulated appetite and opposite for high temp

Question 7

Describe the process of deglutition/swallowing

Answer 7

Oral phase:
Bolus formed and voluntarily moved to pharynx (tongue thckens to push bolus)
Pharyngeal phase:
Pharynx is activated to propel food to oesophagus
Oesophageal phase:
Bolus moves to oesophagus via peristalsis -> stomach

Question 8

Describe the secretory role of the stomach

Answer 8

Exocrine:
- mucin producing cells (cardia, fundus, corpus)
- parietal cells - HCL (fundus and corpus)
- chief cells - pepsinogen + lipase (fundus and corpus)

Endocrine:
- histamine producing/ECL cells (pylorus)
- gastrin producing cells/G cells (fundus and corpus)

Question 9

Describe the neural stimulation of the stomach

Answer 9

Long reflex
Stomach expansion and peptides stimulates secretion via acetylcholine (CNS)

Question 10

Describe the hormonal stimulation of the stomach

Answer 10

short reflex
stomach expansion and peptides => gastrin release + impulse to CNS

Question 11

what is the for mechanism for stomach emptying?

Answer 11

Cajal cells between circular and longitudinal muscle layers stimualte contraction via gap junction to empty stomach
related to mesenteric nerve plexus

Question 12

How is stomach evacuation stimulated?

Answer 12

Decreased gastric pH
wall distension => influx to submucosal plexus => parasympathetic nerve influx to stomach effectors e.g., smooth muscle, parietal cells => evacuation

Question 13

What inhibits stomach emptying?

Answer 13

Stomach emptying is inhibited by duodenal factors, secretin, GIP and CKK

Question 14

What happens when chyme enters duodenum

Answer 14

Chyme enters low pH environment in duodenum which, along with FAs and peptides triggers CKK and secretin release which increase pancreatic juice and bile flow into duodenum and also slows stomach emptying

Question 15

How is peristalsis managed in the SI?

Answer 15

Small intestinal peristalsis and segmentation managed by mesenteric plexus and CNS

Question 16

What stimulates large intestine contraction?

Answer 16

Stomach and duodenum promote large intestine contraction via mesenteric NS (gastro-colic reflex)

Question 17

What are the 4 types of contraction involved in movement of ingesta?

Answer 17

segmentation
peristalsis
antiperistalsis
mass movement

Question 18

Describe the induction of vomiting/emesis

Answer 18

Chemoreceptor zone of the emetic centre lies outside BBB so can be stimulated by toxins in the blood

GI inputs to the emetic centre:
- Cranial nerve X (Vagus) - activated when pharynx is irritated
- Vagal and enteric NS inputs transmit info about GIT, irritation of the GI mucosa activates receptors of these inputs