GI Regulation: Johnson

Question 1

Describe the four functions of the GI tract

Answer 1

Motility
Secretion
Digestion
Excretion

Question 2

Describe the functions of the enteric nervous system and its relationship to the parasympathetic and sympathetic systems

Answer 2

Enteric nervous system is a collection of ganglia comprising the myenteric nerve plexus (located between longitudinal and circular sm. muscle layer of intestines) where signals from the PSNS and the submucosal plexus (which receives SNS innervation) are integrated; also innervates the secretory cells (via SM plexus) and the smooth muscle layers (directly)

PSNS:
Vagus nerve to Myenteric plexus, to submucosal plexus, to secretory cells in mucosa; plexuses deliver signals to smooth muscle layers

SNS:
outflow from sympathetic ganglia to submucosal plexus to secretory cells and smooth muscle layers; doesn’t innervate myenteric plexus directly

Question 3

Describe the differences between endocrine, paracrine and

neurocrine agents

Answer 3

Endocrine = agent is delivered to target via bloodstream
Paracrine = agent is delivered to target which is really close or next door; specificity determined by receptor type and location
Neurocrine = agent is delivered to target from neuron across a synapse

Question 4

Identify the major GI hormones and their functions

Answer 4

1. Gastrin - stimulates acid secretion and mucosal growth
2. Cholecystokinin (CCK) - stimulates pancreas for bicarb/enzyme secretion and growth; stimulates gallbladder for contraction; inhibits gastric emptying
3. Secretin - stimulates pancreatic bicarb secretion and hepatic bile (bicarb) secretion, pancreatic growth; inhibits acid secretion
4. GIP - stimulates insulin release; inhibits acid secretion
5. Motilin - stimulates gastric and intestinal motility (duh)

Question 5

Identify the stimulators for release of the major GI hormones and from where they are released

Answer 5

1. Gastrin - Antrum, D, +/-J; release stimulated by protein, distension, and nerve; inhibited by acid
2. Cholecystokinin (CCK) - D, J, I; release stimulated by protein/fat, secondarily by acid
3. Secretin - D; release stimulated by acid, secondarily by fat
4. GIP - D, J; release stimulated by protein/fat/carbs
5. Motilin - D, J; release stimulated by nerves, secondarily by fat/acid

Question 6

Identify the important neurocrines and their functions in the GI tract

Answer 6

1. VIP - relaxes sphincter and circ. sm. muscle; stimulates intestinal and pancreatic secretion. Vasodilation of BVs (NO synthesis)
2. Bombesin aka GRP - stimulates gastrin release
3. Enkephalins - stimulates sm. muscle contraction, inhibits intestinal secretion

Question 7

Identify the important paracrines and their functions in the GI tract

Answer 7

1. Somatostatin - inhibits gastrin and other peptide hormone release. Inhibits parietal cell secretion of gastric acid.
2. Histamine - stimulates acid release

Question 8

Describe the causes and resulting physiology of pancreatic cholera (Werner-Morrison Syndrome)

Answer 8

• overproduction of VIP
• results in diarrhea, metabolic acidosis, dehydration, and hypokalemia
• high rates of intestinal secretion (because that’s a normal function of VIP)

Question 9

Describe the causes and resulting physiology of gastrinoma (Zollinger-Ellison Syndrome)

Answer 9

• overproduction of gastrin
• results in duodenal ulcer, diarrhea, steatorrhea
• high rates of acid secretion (a normal function of gastrin)
• inactivation of pancreatic lipase

Question 10

Describe the causes and resulting physiology of Pancreatic cholera aka Werner-Morison Syndrome.

Answer 10

• Overproduction of VIP
• diarrhea, metabolic acidosis, dehydration, hypokalemia
• high rates of intestinal secretion