Neural and hormonal control of gastrointestinal function

Question 1

What is responsible for local control of gut function?

Answer 1

Enteric nervous system via interstitial cells of Cajal

Question 2

What is the role of the enteric nervous system?

Answer 2

• regulate contractile activity and secretion of water and salt (mm to cm distances)
• contains basic elements required for complex motor programs (sensory neurons, interneurons, and motor neurons)

Question 3

What is responsible for long-distance control of the gut?

Answer 3

endocrine system; signals to brain, gallbladder, pancreas

Question 4

What is the function of the gut endocrine system?

Answer 4

• secretion of enzymes and solvents into interstitial lumen
• regulation of appetite

Question 5

The myenteric plexus resides

Answer 5

between the longitudinal external smooth muscle and the inner circular smooth muscle

Question 6

The submucosal plexus resides

Answer 6

between the inner circular smooth muscle and the mucosa

Question 7

The submucosal plexus is involved in

Answer 7

control of water and electrolyte secretion

target for many bacterial toxins that produce diarrhoea

Question 8

The myenteric plexus is involved in

Answer 8

main control system of ENS

Question 9

Enterochromaffin cells contain

Answer 9

5-HT (serotonin)

Question 10

What is the general structure of enteroendocrine cells?

Answer 10

• contain one or more different hormones
  
  • eg: serotonin (EC), CCK, secretin, somatostatin, glucagon-like peptides 1 & 2, pancreatic polypeptides, gastrin
• span epithelium:
  
  • apical layer protrudes into gut lumen
  • basolateral surface secretes hormones into interstitial cell space to be taken up by blood vessels (to the liver and body)

Question 11

What is released by enterochromaffin-like (ECL) cells?

Answer 11

histamine; involved in acid secretion in the stomach

Question 12

What modulates the enteric nervous system function?

Answer 12

• vago-vagal reflex pathways
• intestino-intestinal reflexes
• CNS control relating to anticipation, mood, activity

Question 13

What is the vago-vagal reflex pathway?

Answer 13

• coordinate movements in the upper GI
  
  • vagus pathway for control of swallowing
  • vagus regulation of acid secretion in stomach, coordination of contractions in stomach and duodenum

Question 14

What are the intestino-intestinal reflexes?

Answer 14

• some mediated by vagus to brain, others via dorsal root ganglia and SC
• intestinofugal/viscerofugal neurons projecting into gut
  
  • cell bodies in gut wall
  • synapse w/pre-vertebral sympathetic ganglia
    
    • produce reflex inhibition of proxima regions when distal regions are distended, reducing overall flow in the system

Question 15

Sphincter function is directly regulated by

Answer 15

SNS innervation

Question 16

What interactions control gut function?

Answer 16

• GI hormones excite enteric neurons and extrinsic sensory neurons (paracrine) that feed back to the brain
• muscle contraction generated feeds back to the extrinsic circuit and endocrine system
• vagal and sympathetic input modulates ENS circuits
• ICC act as pacemakers of the muscle
  
  • largely independent of neural activity
  • neural activity superimposes a level of excitation or inhibition that modulates contraction; not directly stimulating contraction

Question 17

The cephalic phase of secretion is triggered by

Answer 17

sight, smell, taste, thought of food

Question 18

Activation of the cephalic phase of secretion causes

Answer 18

• increased salivation
• increased gastric acid secretion
• increased secretion of pepsin in the stomach
• relaxation of gastric corpus and fundus (main storage components of the stomach)

Question 19

Cephalic phase of secretion operates by

Answer 19

vagus nerve (no somatic innervation of the gut)

Question 20

The cephalic phase contributes what percent of acid secretion in the stomach?

Answer 20

30%

Question 21

D cells secrete

Answer 21

Somatostatin

Question 22

Somatostatin

Answer 22

inhibits ECL cells from releasing histamine and tf decreases acid release from parietal cells

Question 23

G cells secrete

Answer 23

gastrin

Question 24

G cells are present

Answer 24

in the duodenum and gastric antrum

Question 25

What regulates acid secretion from parietal cells?

Answer 25

• vagus nerve activates ENS neurons in intestinal wall to release ACh:
  
  • activate M3 muscarinic ACh receptors on parietal cells to release acid
  • activate ECL cells to secrete histamine –> activates parietal cells to release acid
  • activate G cells to release gastrin to release acid
  • activate D-cells to release somatostatin –> inhibits ECL cells, G cells, and parietal cells to decrease acid release

Question 26

Gastrin and somatostatin act on parietal cells via

Answer 26

portal vein and liver

Question 27

Swallowing is controlled by

Answer 27

vagus nerve

Question 28

Primary peristalsis is regulated by

Answer 28

vagus nerve and swallowing mechanism via perstaltic mechanism in the brain stem (motor pattern generated by the brain)

Question 29

Secondary peristalsis is regulated by

Answer 29

ENS

Question 30

Distension of the stomach causes

Answer 30

• further relaxation of the stomach
• initial feeling of being full
• activation of enteric and vago-vagal reflexes
  
  • leads to increased acid and pepsin secretion
• stimulates pacemaker activity of ICC cells in antrum to mash food against the pylorus

Question 31

What is the role of the antrum in digestion?

Answer 31

• food and acid entering antrum triggers reflex inhibition of acid secretion in the corpus
• ICC potentials propogate from corpus to pylorus, mashing food against the closed sphincter
• acid, protease, and mechanical activity separates food
  
  • forms a layer of fat that floats to the fundus of the stomach (fat is tf the last thing to exit the stomach)