Mouth

  • This is where the food enters the digestive system[ingestion].
  • Two types of digestion occur here; physical digestion and chemical digestion.
  • Physical digestion is the mechanical breaking up of food into smaller pieces by the teeth. It occurs in the mouth and stomach.
  • Chemical digestion is the breaking down of large food molecules into smaller ones using digestive enzymes which are produced in the mouth.

Oesophagus

  • The food is swallowed and passes on to the oesophagus.
  • Food is pushed down the oesophagus by a wave of muscular contraction called peristalsis.[ The food is now called a bolus]

The Stomach

  • The sphincter muscle opens and allows the bolus of food to enter the stomach.
  • The stomach is a muscular bag.
  • It contains mucus, acid and digestive enzymes.
  • Physical digestion occurs when food is churned in the stomach.
  • Chemical digestion occurs when food is mixed with hydrochloric acid and protein-digesting enzymes.
  • The mixture is now called chyme.
  • The lower sphincter muscle opens and allows the chyme out of the stomach into the small intestine.

The Small Intestine

  • Digestion occurs in the first section of the small intestine.
  • Absorption occurs in the second section of the small intestine.

The Large Intestine

  • The large intestine is about 1.5 metres long.
  • It has a larger diameter than the small intestine.
  • The large intestine absorbs water.
  • It allows undigested food to pass through it. This undigested food is called faeces.
  • The rectum stores the faeces until it is egested through the anus.