Stomach & Small Intestine

Structure of Stomach

Hey all AIPMT Biology Aspirants, in this post we will discuss about STOMACH & SMALL INTESTINE.


  • Stomach is a thick-walled, J-shaped bag-like/sac-like organ that lies on the left side of the body beneath the diaphragm.
  • It connects esophagus to the duodenum, the first part of the small intestine
  • Stomach has four main regions: the Cardiac, Fundus, Body and Pyloric
  • Cardiac surrounds the opening of the esophagus into the stomach. The rounded portion superior to and to the left of the cardiac is the Fundus. Body is the large central portion of the stomach, inferior to the fundus. The Pyloric portion opens into duodenum.
  • Stomach serves as a mixing chamber and holding reservoir of food because a meal can be eaten much more quickly than the intestines can digest and absorb it.
  • Concave medial border of the stomach is called as Lesser Curvature; while convex lateral border is called as Greater Curvature.
  • The wall of the stomach has deep folds (Rugae) of mucosa that disappear as the stomach fills.
  • Two sphincters control the entry and exit of food from the stomach. Esophagus opens into cardiac part of stomach through Cardiac sphincter or Gastroesophageal sphincter of smooth muscles. Pylorus opens into duodenum of the small intestine via a smooth muscle sphincter called the Pyloric sphincter.
Structure of Stomach

Structure of Stomach

Small intestine

  • Small intestine is named so for its small diameter as compared to that of the large intestine
  • Small intestine begins at the Pyloric sphincter of the stomach and eventually ends  into the large intestine
  • Its length is about 3 m in living person and 6 m in cadaver due to loss of smooth muscles tone after death.
  • Small intestine is divided into three regions:Duodenum, Jejunum, Ileum.
  • Duodenum is the first and shortest region. It starts at the pyloric sphincter of the stomach and is in the form of a C-shaped tube (some say it U-shaped too) that extends till it merges with the jejunum.
  • Jejunum is the next middle portion which is coiled in nature and extends to the ileum.
  • Ileum is the final and longest region of the small intestine. It is the highly coiled in nature, which joins the large intestine at a smooth muscle sphincter called the Ileocecal sphincter.
  • Most of the digestion and absorption of nutrients occur in small intestine. Its length provides a large surface area for digestion and absorption, and that surface area is further increased by circular folds, villi, and microvilli.
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