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Chapter 43: Digestion: Anatomy, Biochemistry, and Physiology

A 57-year-old man is being examined by his physician due to complaints of frequent gnawing and burning pain in the middle and upper stomach occurring between meals and most acutely at night. Additional symptoms reported by the patient include heartburn, black stools, and on occasion seeing that his vomit looks like coffee grounds. You suspect the patient is suffering from a peptic ulcer. A defect in which of the following cells in the gastrointestinal tract would most likely be expected given this diagnosis?

A. chief

B. enterochromaffin-like (ECL)

C. enteroendocrine L cells

D. gastric mucus cells

E. parietal

Answer E: Peptic ulcers are painful sores occurring in the lining of the stomach or in the proximal duodenum. One of the most common causes of peptic ulcers is excessive gastric acid secretion from the parietal (oxyntic) cells of the stomach. On rare occasions this excess acid production is due to gastrinomas (Zollinger-Ellison syndrome) of the acid secreting parietal cells.

You are carrying out in vitro experiments that are designed to test the efficacy of novel compounds in the treatment of gastroesophageal reflux disease (GERD). You are testing the various compounds on gastric parietal cells in culture. You discover that one of the compounds exerts a significant inhibition of hydrogen ion (H+) secretion from the cells. This compound most likely mimics the effects of which of the following natural peptides?

A. cholecystokinin

B. gastrin

C. gastrin-releasing peptide

D. GLP-1

E. somatostatin

Answer E: Somatostatin is secreted by enteroendocrine D cells of the stomach and duodenum, δ-cells of the pancreas, and also by the hypothalamus. In the pancreas, somatostatin acts as a paracrine inhibitor of other pancreatic hormones. In the gut, somatostatin is involved in the inhibition of gastric acid secretion. Somatostatin binds to a GPCR called the somatostatin receptor 1 (encoded by the SSTR1 gene) that is coupled to a Gi-type G-protein that inhibits adenylate cyclase. The effect of somatostatin binding to SSTR1 is an antagonism of the gastric acid secreting effects of histamine. Somatostatin can also interfere with the gastric effects of histamine by blocking histamine release from enterochromaffin-like cells (ECL) in the gastric mucosa.

You are tending to a 27-year-old woman whose chief complaint is that she can no longer taste sweetness in food, particularly fruits. You suspect that she may have ...

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