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The Stomach and Duodenum

Table of Contents
The Lungs
The Trachea
The Testes
The Submaxillary Gland
The Liver
The Stomach and Duodenum
The Blood
The Arteries and Veins
The Adipose Tissue
The Skin
The Pituitary Gland
The Pancreas
The Thyroid
The Kidney
The Spinal Cord
The Cerebellum
The Elastic Cartilage
The Bone
The Smooth Muscle
The Striated Muscle


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The stomach is the location of the second step of food digestion (after the mouth) in the digestive system of the body. It is a C-shaped organ located on the left side of the abdominal cavity directly under the heart and diaphragm.


The stomach is responsible for the second part of digestion; after food has been chewed in the mouth, and has traveled down the esophagus, the stomach is responsible for the physical digestion of food and the first part of its chemical digestion as well. The stomach is about 10 inches long, but can expand to hold up to four liters of food, and collapses to a much smaller size when empty.


The stomach, as with the small and large intestine, is made up of several layers of tissues; an inner mucosa layer, made up of epithelial tissue, and blood and lymph vessels, the submucosa, supplying nerves and blood vessels, circular, oblique and longitudinal smooth muscle, and the serosa and mesentery, which covers the digestive organs and holds everything in place.


The inside of the stomach is lined with a thick coating of mucus which protects the stomach from its digestive juices. The inner epithelial layer is dotted with holes called gastric pits, which lead to gastric glands that secrete the stomachs digestive solutions. These solutions include hydrochloric acid and pepsinogen.


 When food enters the stomach from the esophagus, it triggers the release of both solutions, and the interaction with hydrochloric acid causes pepsinogen to convert to pepsin. Hydrochloric acid softens and breaks food apart, kills bacteria and denaturates food proteins, while pepsin breaks proteins into smaller polypeptide chains.


The release of hydrochloric acid and pepsin are controlled by a hormone called gastrin. When the food is ready to leave the stomach, is has been processed into a white, creamy mush called chyme, and is slowly fed into the duodenum of the small intestine through the pyloric sphincter.

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