Human Biology-BY2

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Function of the digestion system

Ingestion - is the taking in of food into the body through the mouth.

Digestion - is the breakdown of large,insoluble food molecules into simple,soluble molecules by means of enzyme.

Mechanical Digestion - the cutting and/or crushing action of the teeth followed by the rhythmical contractions of the gut.

Chemical digestion - involves ezymes secreted by glands outside the gut (Salivary gland,Pancreas) and glands located within the gut wall itself

Absorption - is the passage of digested food through the gut wall into the blood.

Egestion - is the elimination from the body of food that can not be digested e.g. Cellulose cell walls of plants.


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Human Digestion System

The main regions of the human gut are :

  • Mouth
  • Oesophagus (Gullet)
  • Stomach
  • Small Intestine (Duodenum,ileum)
  • Large Intestine
  • Anus

Food is needed as a source of energy for :

  • Movement
  • Synthesis of body tissues
  • Keeping warm
  • Active transport
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Digestion System

Food is propelled along the gut by peristalsis and is processed as it passes through the regions of the gut.


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Structure Of The Mammalian Gut

The gut wall from the mouth to the anus consist of 4 tissue layers surrounding the lumen of the gut :

  • Serosa (Outer Layer)
  • Muscle Layer
  • Sub-Mucosa
  • Mucosa (Innermost Layer )

The muscle layer consists of 2 layers of muscle running in different directions:

  • The inner circular muscle
  • The outer longitudinal layer

The circular muscles contract behind the ball of food to squeeze the food along,while the longitudinal muscles relax.

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The Human Digestion System Diagram


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Large Glands Found Outside The Gut

These Include:

  • Salivary Glands which saliva into the mouth.
  • Liver which secretes bile into the duodenum.
  • Pancreas which secretes pancreatic juice into the duodenum.
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Glands In The Gut

The glands of the gut are of 3 types :

  • Large glands found outside the gut with secretion passing through the tubes or duct into the gut.
  • Glands in the form of cells in the sub-mucosa.
  • Glands in the form of cells in the mucosa.
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