Gastrin

Overview

Diagram illustrating the control of stomach acid secretion.

Gastrin is a peptide hormone that plays a crucial role in the regulation of gastric acid secretion and the maintenance of the gastric mucosa. It is primarily produced by G-cells located in the antrum of the stomach, the duodenum, and the pancreas.

Structure and Synthesis

Gastrin is synthesized as a preprohormone, which is then cleaved to form the active hormone. The most common forms of gastrin are gastrin-17 and gastrin-34, named for the number of amino acids they contain. The synthesis of gastrin is stimulated by the presence of food in the stomach, particularly proteins, and by the vagal nerve stimulation.

Mechanism of Action

Gastrin exerts its effects by binding to the cholecystokinin B receptor (CCK-B receptor) on the parietal cells of the stomach lining. This binding stimulates the secretion of hydrochloric acid (HCl) by the parietal cells, which is essential for the digestion of food and the absorption of nutrients. Gastrin also promotes the growth of the gastric mucosa and increases gastric motility.

Regulation of Gastrin Secretion

The secretion of gastrin is tightly regulated by several factors:

• Stimulation: Gastrin release is stimulated by the presence of partially digested proteins in the stomach, gastric distension, and vagal stimulation via the release of gastrin-releasing peptide (GRP).
• Inhibition: Gastrin secretion is inhibited by the presence of somatostatin, a hormone produced by D-cells in the stomach and duodenum, and by the presence of acid in the stomach, which provides negative feedback to prevent excessive acid production.

Clinical Significance

Abnormal levels of gastrin can lead to various clinical conditions:

• Hypergastrinemia: Excessive levels of gastrin can result in conditions such as Zollinger-Ellison syndrome, where gastrin-secreting tumors (gastrinomas) cause excessive gastric acid production, leading to recurrent peptic ulcers.
• Hypogastrinemia: Low levels of gastrin can be associated with conditions such as atrophic gastritis, where the loss of gastric mucosa leads to reduced acid secretion.

Related Pages

• Stomach
• Peptic ulcer disease
• Cholecystokinin
• Somatostatin