Gastrointestinal Hormones Overview

Questions and Answers

Which of the following is NOT considered an official GI hormone?

Gastrin

Cholecystokinin (CCK)

Insulin (correct)

Secretin

The 'big gastrin' form consists of 17 amino acids.

False

What are the four official GI hormones?

Gastrin, Cholecystokinin (CCK), Secretin, Glucose-dependent insulinotropic peptide (GIP)

The biologic activity of gastrin resides in the last four ______ amino acids.

C-terminal Signup and view all the answers

Match the following types of gastrin with their characteristics:

Little gastrin = Contains 17 amino acids and is secreted in response to a meal Big gastrin = Contains 34 amino acids and is not a dimer of little gastrin Signup and view all the answers

What is one of the primary actions of gastrin?

Increases H⁺ secretion by the gastric parietal cells Signup and view all the answers

Gastrin secretion is stimulated by small peptides and amino acids present in the stomach.

True Signup and view all the answers

What are the two most potent stimuli for gastrin secretion?

Phenylalanine and tryptophan Signup and view all the answers

Gastrin is secreted from the G cells of the gastric ______.

antrum Signup and view all the answers

What effect does gastrin have on the gastric mucosa?

Stimulates the synthesis of RNA and new protein Signup and view all the answers

Patients with gastrin-secreting tumors typically experience atrophy and decreased growth of gastric mucosa.

False Signup and view all the answers

Which type of cells are responsible for secreting gastrin?

G cells Signup and view all the answers

Match the following stimuli with their respective effects on gastrin secretion:

Small peptides = Stimulates gastrin secretion Amino acids = Stimulates gastrin secretion Gastrin-secreting tumors = Causes mucosal hypertrophy Phenylalanine and tryptophan = Most potent stimuli for gastrin secretion Signup and view all the answers

Study Notes

Regulatory Substances in the Gastrointestinal Tract

GI hormones are secreted by endocrine cells in the GI mucosa into portal circulation and exert physiological effects on target cells.
Four recognized GI hormones: gastrin, cholecystokinin (CCK), secretin, and glucose-dependent insulinotropic peptide (GIP).
Other substances are categorized as "candidate" hormones.

Gastrin

Composed of 17 amino acids, referred to as "little gastrin," which is secreted post-meal.
Biologic activity of gastrin is determined by the four C-terminal amino acids.
"Big gastrin" is a longer peptide containing 34 amino acids but is not a dimer of little gastrin.

Actions of Gastrin

Increases H⁺ secretion in gastric parietal cells.
Stimulates growth of gastric mucosa by enhancing RNA synthesis and new protein production.
Gastrin-secreting tumors lead to hypertrophy and hyperplasia of the gastric mucosa.

Stimuli for Gastrin Secretion

Secreted from G cells in the gastric antrum primarily in response to meals.
Secretion triggers from small peptides and amino acids; phenylalanine and tryptophan are the most potent stimuli.
Additional stimuli include:
- Distention of the stomach.
- Vagal stimulation, mediated by gastrin-releasing peptide (GRP).
Atropine does not inhibit gastrin when stimulated vagally since GRP, not acetylcholine (ACh), mediates this effect.

Inhibition of Gastrin Secretion

H+ ions in the stomach lumen provide negative feedback to suppress gastrin release when acidity is adequate.
Somatostatin also acts to inhibit gastrin release.