Gastric juice, Composition and Phases of Gastric Juice Secretion

Gastric juice

Gastric juice is a fluid produced by the inner lining of the gastric mucosa which contains electrolytes, bicarbonates, hydrochloric acid.

All theses substances are very essential for the digestion and absorption of the food inside the small intestine.
  • A typical adult human will secretes about 1.5 liters of gastric acid daily.
  • There are different steps where gastric juice is secreted by different cells and glands of the stomach.
  • Gastrointestinal tract is formed of four different layers from inner to outside- Mucosa, Submucosa, Muscularis propria and Adventitia.
  • Inner lining of the stomach is composed endocrine and exocrine glands and different types of the cells which secretes the various substances essential for the digestion of the food.

Cells of inner Gastric Mucosa

  • Inner lining of the mucosa contains the columnar epithelial cells which secretes the thick mucus which is a kind of glycoprotein.
  • This thick mucus makes the chyme soft for the lubrication of the food and forms a protective layer inside the stomach lining.
  • Mucoid cells secretes the mucus in the pyloric and cardiac part of the stomach.
  • Zymogenic or chief cells are located in gastric glands of the body of the stomach. These cells secretes the pepsinogen which forms the pepsin enzyme for the digestion of the proteins.
  • Gastrin cells or G cells are locate throughout the whole gastric passage and are endocrine in nature secretes the acid stimulating hormone Gastrin.
  • It is secreted in response to lowered acidity of the gastric food contents it enters into the stomach.
  • Parietal cells or oxyntic cells found in glands of the body of stomach. They secretes the hydrochloric acid (HCL).
  • Enterochromaffin cells or endocrine cells of the gastric mucosa secretes the hormone Serotonin.

Composition of Gastric Juice

Composition of Gastric Juice
(Gastric juice)

 Gastric juice is a mixture of various electrolytes - sodium, calcium, potassium, phosphate, bicarbonates and organic and inorganic substances.

Phases of Gastric Juice Secretion

There are three phases where gastric juice is secreted according to the reflex and location of the food passes.
        1. Cephalic phase-    20 to 30% of gastric secretion
        2. Gastric phase     50 to 60% of gastric secretion
        3. Intestinal phase-    5 to 10% of gastric secretion

The phases of gastric secretion are combination of the interrelation and interdependence of the neural and hormonal pathway.

Cephalic phase

This phase is stimulated when the senses send a feedback by- seeing, smelling, taste, or sound. this response is mediated by the 10th cranial nerve or Vagus nerve.

Gastric phase 

  • This phase is mediated by the Vagus nerve and by the release of gastrin. The acidity of the gastric contents should be maintained till 1 hour to 1.5 hours. 
  • Here acid is secreted continuously for the digestion of the proteins which contains the peptides and the amino acids.
  • Gastric phase contains hormonal, mechanical, and chemical factors contributing for the digestion of the food.

Intestinal phase 

  • Small intestine is the major and essential organ of the digestive tract. 
  • The function of this organ is to mixing, transporting, absorption of essential nutrients for the energy production in the body.
  • In this phase duodenum responds to arriving chyme and moderates gastric activity through hormonal secretion and neural reflexes.

Absorption and Emptying

Stomach absorbs few of the products including the glucose, amino acid, fat soluble substances. The pH of the gastric contents determines the absorption of the gastric substances.

The rate of the digestion and the absorption of food depends upon the composition of the meal. 

Fluids are absorbed as fast as solids, proteins and the carbohydrates are more rapidly absorbed than fats and fats are absorbed lastly.

Food particles should in soluble form and reduced in size and cells of the inner lining of gastric mucosa and receptors on lining should be in activated form.  

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