Liver
Stomach
Small intestine
Large intestine
Obtaining nutrition and energy from food is a multi-step process. For true animals, the first step is ingestion, the act of taking in food. This is followed by digestion, absorption, and elimination. The brain is the control center for the sensation of hunger and satiety. The functions of the digestive system are regulated through neural and hormonal responses.
- Our body needs energy and food to move, grow and to stay alive. Our body cells cannot use the food in the form it is eaten by us. Our body changes it into simpler form. The process of changing the food into simpler form is called digestion. The parts of body that take part in the process of digestion form the digestive system.
- The human digestive system, is a coiled, muscular tube (6- 9 meters long when fully extende(d) stretching from the mouth to the anus. The process of digestion occurs in a long tube called alimentary canal.
- Mouth – The process of digestion begins from our mouth. Our teeth break the food into small pieces by cutting and grinding. The tongue mixes food with saliva which is secreted by salivary glands. Saliva starts the digestion of carbohydrates (starch and sugar). After some time, the food in the mouth becomes soft and moist. The tongue pushes this food to the back of our mouth.
- Oesophagus – The chewed food is then pushed from the mouth into the oesophagus. The oesophagus is a large tube that carries food from the mouth to the stomach. The oesophagus uses wave-like muscular movements to push the food to the stomach. These wave-like movements are called peristaltic movements and process is called peristalsis.
- Sometimes peristalsis works in reverse and pushes the food in stomach up and out through mouth. This reverse process of peristalsis is called vomiting. It mostly happens when the food is unsuitable in some way.
- Stomach – Our stomach is a large J-shaped muscular bag. It mixes the food with digestive juice. The digestive juice begins the digestion of proteins (meat, egg, milk, pulses, etc.). The food spends about four hours in the stomach. The digestive juice in the stomach also contains an acid. The acid kills the germs present in our food. It also helps in the digestion of proteins.
- Small Intestine – As food leaves our stomach, it is passed on to the small intestine which is a long, thin tube coiled inside our abdomen. Final digestion of carbohydrates, fats and proteins occurs in the small intestine. Three organs help in the digestion of food here. These are the liver, pancreas and wall of the small intestine. The liver provides bile salts to make fats easier to absorb. The pancreas and intestinal walls secrete juices to digest the remaining food. The absorption of the digested food also occurs in the last part of the small intestine. The inner surface of small intestine has many finger-like structures called villi. The digested food passes into the blood through the walls of the villi. The blood carries food particles to all parts of the body.
- Large Intestine – The undigested part of the food passes into the large intestine. Here the undigested food has a large amount of water. The main job of large intestine is to absorb extra water. The undigested food becomes solid and is called faeces. The faeces is stored in the last part of the large intestine called the rectum. We pass the faeces out of our body through the anus.
The liver, pancreas and gallbladder are not part of the digestive tube, but they are the supporters of our digestive system.
- Liver: The liver produces bile to digest fat. It also breaks down harmful substances in the blood.
- Gallbladder: The liver stores its bile in the gallbladder which releases it into the small intestine.
- Pancreas: The pancreas makes juice to digest remaining carbohydrates, proteins and fats.
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