Digestive System and it's five functions - SEY PHARMA

What is Digestive System?  and it's five functions

 The digestive system comprises of the gastrointestinal tract with various glands attached to it and also known as alimentary canal. It begins at the mouth, passes through the thorax, abdomen and pelvis and ends at the anus. It has a basic structure which is modified at different levels to provide for the processes occurring at each level. The digestive processes gradually break down the foods eaten until they are in a form suitable for absorption.

Five function of Digestive system :

Ingestion :

This is the taking of food into the alimentary tract, i.e. eating and drinking.

Propulsion : 

This mixes and moves the contents along the alimentary tract.

Digestion : 

This consists of :

     • mechanical breakdown of food by, e.g. mastication (chewing).

     • chemical digestion of food into small molecules by enzymes present in secretions produced by glands and accessory organs of the digestive system.

Absorption : 

This is the process by which digested food substances pass through the walls of some organs of the alimentary canal into the blood and lymph capillaries for circulation and use by body cells.

Elimination : 

Food substances that have been eaten but cannot be digested and absorbed are excreted from the alimentary canal as faeces by the process of defaecation.

Fig: Digestive system with different organ

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

How acid is produce in Stomach? - SEY PHARMA

 How acid is produce in Stomach?

     Gastric acid or gastric juice is a digestive fluid formed in the stomach and is composed of hydrochloric acid, potassium chloride and sodium chloride. Gastric acid is produced by the cells in the lining of the stomach, which are coupled in feedback systems to increase acid production when needed. These cells also produce mucus, which form a viscous physical barrier to prevent gastric acid damaging the stomach. The main constituent of gastric acid is hydrochloric acid which is produced by parietal cells in the gastric glands of the stomach. Parietal cells contains an extensive secretory network from which hydrochloric acid is secreted into the lumen of stomach. In the human lumen stomach, the acidity being maintained by the proton pump H+/K+ ATPase. Chloride and sodium ions are actively secreted from cytoplasm of parietal cells into the lumen of canaliculus.

CO2, and Cl- diffuse form the blood into the stomach cell. Within the cell, CO2, combines with H,O, in presence of CA enzyme to form H2CO3. H2CO, dissociates into HCO3(-), and H+. HCO3(-), is absorbed to blood in exchange of Cl- which subsequently diffuse to gastrioc lumen and combines with H+ to form HCl.

Fig: acid production in Stomach