Small Intestine.

 

Small Intestine:

  • It is present between the stomach and large intestine.

  • It starts at duodenum and ends at ileocaecal junction.

  • It lies in the abdominal cavity surrounded by large intestine.

  • Length is  5 Meters and diameter is 1.5 inches.

  • Provides Chemical as well as mechanical digestion.

  • Main site for chemical digestion and absorption of food.

  • Contains “Three” parts,

    1. Duodenum

    2. Jejunum.

    3. Ileum.

  1. Duodenum.

    • First part.

    • Starts near the pyloric sphincter of the stomach.

    • “C” shaped.

    • Smallest part is only 25 cm.

    • Contains openings of bile duct and pancreatic duct.

    • It has little acidic pH.

  1. Jejunum.

  • Middle part.

  • Present between duodenum and ileum.

  • 3 Feet in length.

  1. Ileum.

  • Last part.

  • Starts after jejunum and ends at the large intestine at “Ileocaecal Junction”.

  • Contains ileocaecal sphincter.

  • 6 feets in length.

  • Cells of Small Intestine:

    1. Absorptive Cells:

      • Modified columnar epithelium.

      • Contains “Microvilli '' provides greater surface area.

    2. Paneth Cells:

      • Secrete antimicrobial substances.

      • Protects from microorganisms survived from stomach acid.

    3. Enteroendocrine Cells:

      • Cells with endocrine functions.

      • S cells : Secretin (Regulates secretions of Pancreas and Liver.

      • ICells: Secretes Cholecystokinin (Regulates secretion of Bile.)

      • K Cells: Secrete a glucose dependent peptide that stimulates secretion of insulin.

      • G Cells: Secrete “Gastrin”. (Stimulates Gastric Acid Secretion).

    4. Goblet Cells: Secrete Mucus.

  • Functions of Small Intestine:

    1. Forward movement of food by peristalsis governed by ANS.

    2. Secretion of Intestinal Juice, (Governed by ANS).

    3. Absorption of nutrients and Vitamins.

    4. Secretion of Secretin and Gastrin.

    5. Mechanical and Chemical Digestion.

Movements of Small Intestine:

  • Small intestine shows two types of movements,

    • Peristalsis.

    • Segmentation.

  • Peristalsis:

    • It is a spontaneous contraction and relaxation of “Longitudinal Muscles”.

    • Results in forward movement of food.

    • It is in a single direction i.e. towards anus.

    • Controlled by “ANS” (Ach increases while Adr decreases).

  1. Segmentation: 

    • It is a spontaneous contraction and relaxation of “Circular  Muscles”.

    • Results in forward and backward movement of food.

    • It is in two directions.

    • Not controlled by ANS, it is Myogenic in nature.

“Watch This Video”.

Commonly Asked Questions:

  1. Write a short note on Human Small Intestine.

  2. Write a short note on the movements of smooth muscles in the small intestine.

  3. Name different special cells of the small intestine with their function.

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