GI secretory products

Question 1

Intrinsic factor

Answer 1

Source: Parietal cells (stomach)

Action: Vitamin B12-binding protein (required for B12 uptake in terminal ileum)

Regulation:
Notes: Autoimmune destruction of parietal cells -> chronic gastritis and pernicious anemia.

Question 2

Gastric acid

Answer 2

Source: Parietal cells (stomach)

Action: Decreased stomach pH

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

Notes: Gastrinoma: gastrin secreting tumor that causes continuous high levels of acid secretion and ulcers.

Question 3

Pepsin

Answer 3

Source: Chief cells (stomach)

Action: Protein digestion

Regulation: Increased by vagal stimulation, local acid

Notes: Inactive pepsinogen -> pepsin by H+.

Question 4

HCO3-

Answer 4

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

Action: Neutralizes acid

Regulation: Increased by pancreatic and biliary secretion with secretin

Notes: HCO3- is trapped in mucus that covers the gastric epithelium.