Enzymes and Digestion

• Starch, proteins and fats are big molecules. They're too big to pass through the walls of the digestive system, so digestive enzymes break these big molecules down into smaller ones like sugars (e.g. glucose and maltose), amino acids, glycerol and fatty acids. These smaller, soluble molecules can pass easily through walls of the digestive system, allowing them to be absorbed into the blood stream.
• Amylase is an example of a carbohydrase. It is made in the salivary glands, the pancreas and the small intestine. It breaks down starch into maltose.
• Proteases are made in the stomach (it's called pepsin there), the pancreas and the small intestine. It converts proteins into amino acids.
• Lipases are made in the pancreas and the small intestine. They convert lipids into glycerol and fatty acids.
• The body makes good use of the products of digestion. They can be used to make new carbohydrates, proteins and lipids. Some of the glucose (a carbohydrate) that's made is used in respiration.
• Bile is produced in the liver. It's stored in the gall bladder before it's released into the small intestine.
• The hydrochloric acid in the stomach makes the pH too acidic for enzymes in the small intestine to work properly. Bile is alkaline - it neutralises the acid and makes conditions alkaline. The enzymes in the small intestine work best in these alkaline conditions.
• Bile emulsifies fat and breaks it down into tiny droplets. This gives a much bigger surface area of fat for the enzyme lipase to work on - which makes it's digestion faster.
• Enzymes used in the digestive system are produced by specialised cells in glands and in the gut lining.
• Different enzymes catalyse the breakdown of different food molecules.
• Salivary glands produce amylase enzyme in the saliva.
• The gullet is another word for the oesophagus.
• The liver is where bile is produced. It neutralises stomach acid and emulsifies fat.
• The gall bladder is where bile is stored before it's released into the small intestine.
• The large intestine is where excess water is absorbed from the food.
• The stomach pummels food with its muscular walls; produces the protease enzyme, pepsin and produces hydrochloric to not only kill bacteria but also give the right pH for the protease enzyme to work.
• The pancreas produces protease, amylase and lipase enzymes. It releases these into the small intestine.
• The small intestine produces protease, amylase and lipase enzymes to complete digestion and absorbs digested food out of the digestive system into the blood.
• The rectum is where the faeces (made up of indigestible food) are stored before they leave through the anus.