What Are G Cells?
G cells, also known as gastrin cells, are a type of enteroendocrine cell located primarily in the antrum of the stomach and occasionally in the duodenum. These cells are responsible for the secretion of the peptide hormone
gastrin, which plays a crucial role in the regulation of gastric acid secretion.
Where Are G Cells Located?
G cells are predominantly found in the mucosal lining of the stomach, specifically in the antrum region. They can also be located in smaller numbers in the duodenum. Their positioning is strategic for their role in stimulating the gastric parietal cells to secrete hydrochloric acid.
What Is the Function of G Cells?
The primary function of G cells is to secrete
gastrin in response to various stimuli, such as the presence of peptides and amino acids in the stomach. Gastrin then stimulates the parietal cells of the stomach to produce and secrete gastric acid (HCl). This gastric acid is essential for the digestion of food and the absorption of nutrients.
How Do G Cells Secrete Gastrin?
The secretion of gastrin by G cells is a well-regulated process. When food enters the stomach, it triggers the release of gastrin from G cells into the bloodstream. This hormone then travels to the
parietal cells located in the gastric glands of the stomach lining, prompting them to secrete hydrochloric acid. Additionally, gastrin can stimulate the growth of the gastric mucosa and increase the motility of the stomach.
The presence of food, especially proteins and amino acids, in the stomach.
Distension of the stomach wall due to food intake.
Vagal nerve stimulation, which releases acetylcholine.
Hormonal signals, such as the release of
gastrin-releasing peptide (GRP).
What Inhibits G Cells?
The activity of G cells can be inhibited by several mechanisms to prevent excessive acid production. These include:
Low pH levels in the stomach, which signal sufficient acid production.
The hormone
somatostatin, released by D cells, which directly inhibits G cells.
Negative feedback mechanisms involving other regulatory peptides and neurotransmitters.
What Is the Histological Appearance of G Cells?
Under the microscope, G cells can be identified by their location in the gastric glands and their characteristic granular appearance. They contain numerous secretory granules, which are visible in histological sections stained with special techniques like immunohistochemistry. The granules contain gastrin, which can be visualized using specific antibodies.
Pathological Conditions Involving G Cells
Abnormalities in G cell function can lead to various gastrointestinal disorders. For instance: Hypergastrinemia: Excessive secretion of gastrin, often due to conditions like Zollinger-Ellison syndrome, leading to increased gastric acid production and peptic ulcers.
Hypochlorhydria: Reduced gastric acid secretion, which can be caused by atrophic gastritis or the use of proton pump inhibitors, leading to impaired digestion and nutrient absorption.
Clinical Significance of G Cells
The clinical relevance of G cells extends to diagnostic and therapeutic applications. Measurement of serum gastrin levels can aid in the diagnosis of conditions like Zollinger-Ellison syndrome and chronic atrophic gastritis. Additionally, targeting the pathways that regulate G cell activity can help manage acid-related disorders.
Conclusion
G cells play a pivotal role in the regulation of gastric acid secretion, impacting digestion and overall gastrointestinal health. Understanding their histological characteristics, regulatory mechanisms, and clinical significance is essential for diagnosing and treating various gastric disorders.
