GI regulatory substances

Question 1

Cholecystokinin (CCK)

Answer 1

Source: I cells (duodenum, jejunum)

Action: Increases pancreatic secretion and gallbladder contraction. Decreases gastric emptying

Regulation: Increased by fatty acids and amino acids

Notes: CCK acts on neural muscarinic pathways to cause pancreatic secretion

Question 2

Gastrin

Answer 2

Source: G cells (antrum of stomach)

Action: Increases gastric H+ secretion, growth of gastric mucosa, increases gastric motility

Regulation: Increased by stomach distention/alkalinization, amino acids, peptides, vagal simulation. Decreased by stomach pH

Question 3

GIP

Answer 3

Source: K cells (duodenum, jejunum)

Action: Decreases H+ secretion

Regulation: Increased by fatty acids, amino acids, oral glucose

Question 4

Motilin

Answer 4

Source: Small intestine

Action: Produces migrating motor complexes

Regulation: Increased in fasting state

Notes: Motilin receptor agonists (eg erythromycin) are used to stimulate intestional peristalsis

Question 5

Secretion

Answer 5

Source: S cells (duodenum)

Action: Increases pancreatic HCO3- secretion, Increases bile secretion, decreases gastric acid secretion

Regulation:

Question 6

Somatostatin

Answer 6

Source: D cells )pancreatic islets, GI mucosa)

Action: Decreases: gastric acid and pepsinogen, pancreatic and small intestine fluid secretion, gall bladder contraction

Regulation: Increased by acid. Decreased by vagal stimulation

Notes: Inhibitory hormone. Antigrowth hormone effects (inhibits digestion and absorption)

Question 7

Nitric Oxide

Answer 7

Source:

Action: Increases smooth muscle relaxation, including LES

Regulation:

Notes: loss of NO secretion is implicated in increased LES tone of achalasia

Question 8

Intrinsic factor

Answer 8

Source: Parietal cells (stomach)

Action: Vitamin B12 binding protein

Regulation:

Notes: Autoimmune destruction of parietal cells can lead to chronic gastritis and pernicious anemia

Question 9

Gastric acid

Answer 9

Source: Parietal cells (stomach)

Action: Decreases stomach pH

Regulation: Increased by histamine, ACh, and gastrin. Decreased by somatostatin, GIP, prostaglandin, secretion

Question 10

Pepsin

Answer 10

Source: Chief cells (stomach)

Action: Protein digestion

Regulation: Increased vagal stimulation, local acid

Question 11

HCO3-

Answer 11

Source: Mucosal cells (stomach, duodenum, salivary glands, pancreas) and Brunner gland (duodenum)

Action: Neutralizes acid

Regulation: Increased by pancreatic and biliary secretion with secretin

Note: HCO3 is trapped in mucus that covers the gastric epithelium