GI regulatory substances

Question 1

Gastrin

Answer 1

G cells (antrum of stomach, duodenum)

• gastric H+ secretion (mainly via ECL cells)
• growth of gastric mucosa
• gastric motility

(+) stomach distention/ alkalinization, amino acids, peptides, vagal stimulation
(-) pH

Question 2

Somatostatin

Answer 2

D cells (pancreatic islets, GI mucosa)

• decrease gastric acid and pepsinogen secretion
• decrease pancreatic and small intestine fluid secretion
• decrease gallbladder contraction
• decrease insulin and glucagon release

(+) acid
(-) vagal stimulation

Question 3

Cholecystokinin

Answer 3

I cells (duodenum, jejunum)

• Increase pancreatic secretion (via neural muscarinic path)
• Increase gallbladder contraction
• Decrease gastric emptying
• Increase sphincter of Oddi relaxation

(+) fatty acids, amino acids

Question 4

Secretin

Answer 4

S cells (duodenum)

• pancreatic HCO3– secretion
• decreased gastric acid secretion (via gastrin inhibition)
• bile secretion

(+) acid, fatty acids in lumen of duodenum

Question 5

Glucose-dependent Insulinotropic Peptide (GIP)

Answer 5

K cells (duodenum, jejunum)
Exocrine: decreased gastric H+ secretion
Endocrine: increased insulin release

(+) fatty acids, amino acids, oral glucose

Question 6

Motilin

Answer 6

Small intestine
- Produces migrating motor complexes (MMCs)

(+) fasting state

Question 7

Vasoactive Intestinal Polypeptide (VIP)

Answer 7

Parasympathetic ganglia in sphincters, gallbladder, small intestine

• Increase intestinal water and electrolyte secretion
• Increase relaxation of intestinal smooth muscle and sphincters

(+) by distention and vagal stimulation
(-) adrenergic input

Question 8

Nitric Oxide

Answer 8

• smooth muscle relaxation, including lower esophageal sphincter (LES)

Question 9

Peptide YY

Answer 9

Colon, ileum

- decreases histamine release from enterochromaffin cells causing decreased acid

Question 10

Intrinsic factor

Answer 10

Parietal cells (stomach)
 - Vitamin B12–binding protein (required for B12 uptake in terminal ileum)

Question 11

Gastric Acid

Answer 11

Parietal cells (stomach)
 - Decreases stomach pH

(+) histamine, ACh, gastrin
(-) somatostatin, GIP, prostaglandin, secretin

Question 12

Pepsin

Answer 12

Chief cells (stomach)
 - Protein digestion

(+) vagal stimulation, local acid

Question 13

HCO3-

Answer 13

Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner glands (duodenum)
- Neutralizes acid

(+) pancreatic and biliary secretion with secretin

Question 14

Vagal NT’s

Answer 14

ACh on parietal cells

Gastrin Releasing Peptide (GRP) on G cells