Digestion

• In the mouth (Buccal cavity), Food is chewed by molar teeth. The teeth breaks food into smaller lumps. This is physical digestion.

• During chewing, saliva, containing enzymes and mucus is added to the food. Amylase, one enzyme, starts to break down starch. This is the first stage of chemical digestion. Mucus makes food into a smooth paste allowing easy swallowing.

• Food is rolled into a ball and swallowed. It passes down the oesophagus by contraction of muscles (peristalsis).

• In the stomach, hydrochloric acid kills micro-organisms, breaks up food, and provides optimum conditions for stomach enzymes.

• The muscles in the stomach wall contract and mix the food (physical digestion) into a liquid called chyme.

• Pepsin is added to digest proteins.

• small amounts of chyme are released into the first part of the small intestine (duodenum), where bile made in teh liver and stored in the gall bladder, neutralises the acid from the stomach. Bile also breaks fat into small droplets allowing digestion by the enzyme lipase (made in pancreas).

• Sucrase, amylase, and protease enzymes made in the pancreas and intestinal glands are released into the chyme to digest carbohydrates and proteins. In grass eating mammals, a large blind pouch called the caecum contain micro-organisms that produce enzyme cellulase needed to digest cellulose in grass and plants.