G cell

G cells are specialized endocrine cells located in the stomach lining, particularly in the antrum region, which is the lower third part of the stomach. They play a crucial role in the digestive system by secreting the hormone gastrin into the bloodstream. Gastrin, in turn, stimulates the parietal cells in the stomach lining to produce hydrochloric acid (HCl), which is essential for the digestion of food, especially proteins. The regulation of acid secretion by G cells is a vital process in maintaining the digestive system's health and preventing conditions such as peptic ulcers and gastritis.

Function

The primary function of G cells is to produce and secrete gastrin in response to certain stimuli, including the presence of amino acids and peptides in the stomach, an increase in stomach pH, and vagal stimulation through the neurotransmitter acetylcholine. Gastrin has several important effects on the gastrointestinal system:

• It stimulates the secretion of hydrochloric acid by parietal cells.
• It promotes the growth of the gastric mucosa and increases the mass of the parietal cells.
• It enhances the motility of the stomach to mix food with digestive juices.

Regulation

The secretion of gastrin by G cells is regulated by a feedback mechanism involving the acidity of the stomach. When the pH of the stomach decreases (becomes more acidic), gastrin secretion is inhibited. This prevents excessive acidity that could damage the stomach lining. Additionally, the hormone somatostatin can inhibit gastrin release from G cells, providing another layer of regulation.

Pathology

Abnormalities in G cell function can lead to various gastrointestinal disorders. For example, an excess of gastrin secretion can cause Zollinger-Ellison syndrome, a condition characterized by the formation of peptic ulcers due to increased gastric acid production. Conversely, a deficiency in gastrin can lead to a reduction in stomach acid, impairing digestion and absorption of nutrients.

Location

G cells are predominantly found in the antrum of the stomach, with a higher concentration towards the pylorus, which is the opening to the duodenum. Their strategic location allows them to effectively sense the chemical composition of the stomach contents and respond appropriately by adjusting gastrin secretion.

Clinical Significance

Understanding the function and regulation of G cells is important in the diagnosis and treatment of various gastrointestinal diseases. Measurement of gastrin levels in the blood can be used to diagnose conditions like Zollinger-Ellison syndrome. Moreover, drugs that inhibit gastric acid secretion, such as proton pump inhibitors (PPIs) and H2 receptor antagonists, can indirectly affect G cell activity by altering the feedback regulation of gastrin secretion.

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  G_cell
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  G_cell hyperplasia - very high magnification