Regulation of Acid Production through Parasympathetic Nervous System - SEY PHARMA

How does acid production regulate through Parasympathetic Nervous System?

  Gastric. acid production is regulated by both autonomous nervous system and hormones. The parasympathetic nervous system via vagus nerve and the hormone gastrin stimulates parietal cells to produce acid secretion. The production of gastric acid in the stomach involves four types of cells in this process : parietal cells, G cells, D cells and enterochromaffine like cells.

  There are three phases in the secretion of gastric acid which increase the secretion rate in order to digest a meal.

Regulation of secretion of gastric juice

       There are three phases of secretion of gastric juice

1.Cephalic phase : 

This flow of juice occurs before food reaches the stomach and is ? due to reflex stimulation of the vagus (parasympathetic) nerves initiated by the sight, smell or taste of food. When the vagus nerves have been cut, this phase of gastric secretion stops. Sympathetic stimulation, e.g. during emotional states, also inhibits gastric activity.

2.Gastric phase : 

When stimulated by the presence of food the enteroendocrine cells in the pylorus and duodenum secrete the hormone gastrin, which passes directly into the circulating blood. Gastrin, circulating in the blood which supplies the stomach, stimulates the gastric glands to produce more gastric juice. In this way secretion of digestive juice is continued after completion of a meal and the end of the cephalic phase. Gastrin secretion is suppressed when the pH in the pylorus falls to about 1.5. 

3.Intestinal phase : 

When the partially digested contents of the stomach reach the small intestine, two hormones, secretin and cholecystokinin, are produced by endocrine cells in the intestinal mucosa. They slow down the secretion of gastric juice and reduce gastric motility.

By slowing the emptying rate of the stomach, the chime in the duodenum becomes more thoroughly mixed with bile and pancreatic juice. This phase of gastric secretion is most marked following a meal with a high fat content. The rate at which the stomach empties depends largely on the type of food eaten. A carbohydrate meal leaves the stomach in 2 - 3 hours, a protein meal remains longer and a fatty meal remains in the stomach longest.

Fig: The three phases of secretion of gastric juice