Small and Large Intestine

Biology

definition

Small intestine

Structure:
The small intestine has three sub-regions:
  • Duodenum: C- shaped
  • Jejunum: A long coiled middle portion 
  • Ileum: Highly coiled. It opens in the large intestine. 
The walls of the small intestine have finger-like foldings called villi. The cells which line the villi produce many small projections called microvilli. 
Villi are supplied with a network of capillaries and a large lymph vessel called the lacteal. 
Mucosa epithelium has goblet cells. They secrete mucus which helps in lubrication. Mucosa also forms crypts in between the bases of villi in the intestine (crypts of Lieberkuhn).
Functions:
  • It serves for both digestion and absorption.
  • It receives two digestive juices; the bile and pancreatic juice.
  • Ileum is very long, has large villi and made up of single epithelium, which helps in absorption of food.

definition

Large intestine

Structure:
The large intestine is shorter but wider than the small intestine. It is about 1.5 meters long. 
It has three parts:
  1. Caecum- The caecum is situated at the junction of the small and large intestine (ileocaecal junction). It consists of some symbiotic microorganisms. The vermiform appendix arises from the caecum. It is a narrow finger-like tubular projection. The appendix is a vestigial organ. It helps to digest cellulose by bacterial action.
  2. Colon- The colon is divided into three parts- an ascending, a transverse and descending part. The descending part opens into the rectum. It absorbs water and some remnants of digested food.
  3. Rectum- Rectum temporarily stores undigested food and waste, to be defecated through the anus.
Functions:
The large intestine has following functions:
  1. Absorption of water
  2. Formation of feces
  3. Temporary storage of feces
  4. Elimination of feces
  5. Production of mucus for lubrication
  6. The colon bacteria produce vitamins B and K which are absorbed.