Explain Human Digestive system..................
Answers
Digestive organs and glands and their functions
(i) Mouth: Digestion of food begins in the mouth. The mouth comprises of the following:
Teeth : They tear and break down the food.
Saliva : The salivary glands secrete saliva. In the digestion process, the saliva helps the teeth and tongue to masticate and mix up the food thoroughly. Mucus in saliva helps in lubricating and adhering food particles into a bolus. Then the bolus conveyed to pharynx for further digestion. Lysozyme present in saliva acts as an antibacterial agent that prevents infection. They also secrete a digestive enzyme called salivary amylase, which breaks down starch into sugar.
Tongue : It is a sense organ with taste buds, which help us to differentiate between various food items. The muscular movements in the tongue move the food from the mouth into the throat, or pharynx.
(ii) Pharynx: It is a common passageway for food and air. It opens into the oesophagus (which leads to the stomach) and trachea (which leads to the lungs).
(iii) Oesophagus: The circular smooth muscles in the oesophagus contract when food is swallowed. This prevents the chewed food material from moving back into the mouth. This is followed by the contractions and relaxations of the longitudinal smooth muscles, which push the digested food forward. These movements are called peristaltic movements, which push the food into the stomach.
(iv) Stomach: The stomach stores and mixes the food received from the oesophagus with the gastric juice. The gastric glands present in the walls of the stomach secrete several substances, which together constitute the gastric juice.
The main components of gastric juice are hydrochloric acid, mucus, and pepsinogen.
Hydrochloric acid dissolves bits of food and creates an acidic medium. In this medium, pepsinogen is converted to pepsin, which is a protein-digesting enzyme.
The food from the stomach passes into the small intestine.
(v) Small intestine: It is the longest part of the alimentary canal. It is made up of three parts- duodenum, jejunum, and ileum.
The small intestine produces intestinal juice from the glands present in the wall, which helps in further digestion of food.
Digestive juices from two glands, namely the liver and pancreas mixes with the food in the small intestine.
The liver produces bile juice (which causes emulsification of fats) and the pancreas produces pancreatic juice (for digesting proteins and emulsified fats).
The small intestine is the site for complete digestion of carbohydrates, proteins, and fats.
This digested food is then absorbed through the intestinal walls. The inner lining of the small intestine has millions of tiny finger-like projections called the villi . These projections increase the surface area of the small intestine for more efficient food absorption.
Within these villi, the capillaries absorb nutrients from the digested products of proteins and carbohydrates and lead them into the blood stream.
(vi) Large intestine: The indigestible material and water enters the large intestine. It also has villi to absorb water and some vitamins from the undigested food. This absorption of water helps to compact the faeces. It also performs the function of storage of wastes before they are excreted from the body via the anus.
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