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.