The digestive system The human body needs food and drink to survive. The things we eat and drink must first be turned into substances the body can use. This process is called digestion. Digestion begins in the mouth where food is mashed up by the teeth and tongue. Saliva softens the food, ready for swallowing. The food travels down the oesophagus into the stomach, where powerful acids change it into a mush. This then squeezes into the small intestine, where it mixes with juices from the pancreas and gall bladder. Any useful substances pass through the walls of the small intestine and are taken by the blood to the liver. The liver processes these useful substances and stores some of them. Waste products are pushed out of the body through the large intestine and the rectum.
The body needs energy to power its chemical life processes. It also needs raw materials for maintenance, growth and repair. The energy and raw materials are in our food. Digestion is the process of taking in, or eating, food and breaking it down into tiny pieces, small enough to pass into the blood and be carried all around the body. The parts that take in and break down food are known as the digestive system.
Faeces are 75% water, 25% solids. The solids are made up of roughly one third undigested fats and proteins, one third indigestible cellulose and one third bacteria.
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