Gastrointestinal Hormones Overview

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

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

What are the four official GI hormones?

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

Match the following types of gastrin with their characteristics:

What is one of the primary actions of gastrin?

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

What are the two most potent stimuli for gastrin secretion?

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

What effect does gastrin have on the gastric mucosa?

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

Which type of cells are responsible for secreting gastrin?

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

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.

Zollinger-Ellison Syndrome

Characterized by gastrin secretion from non-β-cell tumors in the pancreas, leading to excessive gastric acid production.

Explore the key regulatory substances in the gastrointestinal tract, focusing on the four official GI hormones: gastrin, cholecystokinin, secretin, and glucose-dependent insulinotropic peptide. Understand their release mechanisms from endocrine cells and their physiological actions on target cells.