The Mouth

The mouth performs two functions:

1. Mechanical digestioninvolves chewing – teeth chop and grind food into small pieces.

2. Mixing food with salivasaliva starts the break down of carbohydrates (starch) using an enzyme called amylase.

Amylase

The Oesophagus

After being swallowed the food travels down the oesophagus.

The Stomach

The stomach continues to mix the food with digestive enzymes. Amylase continues to digest carbohydrates

Proteins are digested in the stomach and small intestine. Protease enzymes break down proteins into amino acids. Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful micro-organisms that may be in the food.

O

Protease

Small Intestine Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on.

Lipase

The Small Intestine- Microvilli

The inside of the intestine is folded and covered in microvilli. The microvilli increase the surface area of the intestine to increase the absorption of carbohydrates, amino acids and fats

Large Intestine

By the time food reaches the large intestine all useful nutrients have been absorbed into the blood. All that remains are waste products of digestion and water.

The water is very valuable so is absorbed into the blood stream

Waste products pass through the large intestine to be stored in the rectum before passing out of the anus as faeces.

The appendix is used to help some animals digest cellulose in plants. In humans the appendix has a very limited role as humans do not need to digest cellulose for carbohydrates.

Liver and Pancreas

The liver and the pancreas play important part in digestion. The liver produces bile, which helps the digestion of fat.

The pancreas produces chemicals called digestive enzymes such as:

• Protease - proteins• Carbohydrase (amylase)

- carbohydrates• Lipase - fats