Q1. From where does the digestion starts in human? .
Q2.Write two function of saliva .
Q3. What is the role of liver in digestive system?
Q4. Name the juice secreted by liver.
Q5. write the function of a. Small intestine
b. Large intestine
Q6. What are villi?
Q7. From where does food gets egested.
Q8.Write the function of hydro chloric acid in stomach.
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Answers
There are different parts of the human digestive system are mouth, oesophagus, liver, stomach, pancreas and intestine.
(a) Mouth: The mouth is the beginning of the alimentary canal where the teeth break up the food. This crushed food mixes with saliva that is secreted by the salivary glands which help the food to pass smoothly through the soft lining of the alimentary canal. In the mouth, the enzyme salivary amylase breaks down starch into simple sugar maltose. Hence, digestion begins in the mouth itself.
(b) Stomach: The stomach is 'J' shaped and lies on the left side of the abdomen. It receives the partly digested food which enters through the esophagus. Due to peristaltic movement of contraction and relaxation of the muscles, the food is pushed forward in the canal. The gastric glands lying in the walls of the stomach secrete three gastric juices, they are hydrochloric acid, enzymes pepsin and mucus. Hydrochloric acid creates acidic conditions so that the enzyme pepsin is able to digest proteins. Under normal conditions, mucus protects the inner lining of the stomach, from the action of acids. The food is churned by the muscular walls of the stomach and the gastric juices are properly mixed. The sphincter muscle helps in releasing the partly digested food into the small intestine.
(c) Intestine: The small intestine is 5-6 m in length and is the longest part of the alimentary canal. The Large intestine is 1.5 m in length. It is fitted into a compact space in the belly by extensive coiling and has a small diameter. In the small intestines, carbohydrates, fats and proteins are fully digested. For this purpose, the acidic food from the stomach is first made alkaline. The liver is the largest gland, secretes bile juice which is stored in the gall bladder. When food enters the small intestine, bile is released through a duct. Bile makes the food alkaline and also breaks the large fat globules into smaller ones, increasing the enzyme action. Pancreas secretes pancreatic juice and has digestive enzymes like Trypsin which digests proteins, lipase which breaks down fats ad pancreatic amylase which digests carbohydrates. The bile and the pancreatic juice enter the small intestine through a common duct. The walls of the small intestine also secretes some intestinal juices, this completes the digestion process of converting proteins to amino acids, complex carbohydrates to glucose and fats into fatty acids. In the small intestines the digested food is absorbed by the villi, which are finger like projections and are richly supplied with blood vessels. Absorption of water and salts takes place in large intestine and undigested food is thrown out of the body through anus.
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