17. Why are villi present in the intestine
and not in the stomach?
1.The villi are the units of absorption consisting of the lacteal duct in the middle surrounded by a fine network of blood capillaries.
2.Digestion is completed in the small intestine and maximum absorption takes place in the small intestine only.
3. Hence, the villi are found only in small intestine. A very small amount of substance is absorbed from the stomach.
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18. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?
1.Bile is produced by the Liver. The Bile duct from the liver joins the pancreatic duct and pours its secretions into the duodenum.
2.The bile contains bile pigments (bilirubin and biliverdin) as the break down products of haemoglobin of dead RBCs, bile salts, cholesterol and phospholipids but has no enzymes.
3.Bile helps in emulsification of fats. Bile salts reduce the surface tension of fat droplets and break them into small globules. Bile also activates lipases to digest lipids.
4.Thus the bile is very important for digestion through it does not contain any enzyme.
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19. List the chemical changes that starch molecule undergoes from the time it reaches the small intestine.
1.When the food reaches the first part of the small intestine i.e. the duodenum, pancreatic juices and bile juice act on it.
2. Enzymes for starch digestion are present in the pancreatic juice. Pancreatic amylase converts glycogen and starch into maltose.
3. The enzymes in the intestinal juice (succus entericus) act further on the products of pancreatic digestion.
Maltase, Lactase, Sucrase act on the sugars.
20. How do proteins differ from fats in their
energy value and their role in the body?
| Proteins | Fats |
| The caloric value and physiological fuel value of 1 gram of protein is 5.65 Kcal and 4 Kcal respectively | Fat has a caloric value of 9.45 Kcal and a physiological fuel value of 9 Kcal per gram. |
| Proteins are required for growth and repair of body cells. | Fats are the best reserve food stored in our body which is used for production of energy |
| They are stored in the body only to a certain extent. The body requires 65-75 gm of proteins per day. | The body requires 60-70 gm of fats per day |
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21. Digestive secretions are secreted only when needed. Discuss.
The activities of the gastro-intestinal tract are carried out by the neural and hormonal control for proper coordination of different parts. Gastric and intestinal secretions are stimulated by neural signals. Hormonal control of the secretion of digestive juices is carried out by local hormones produced by the gastric and intestinal mucosa. Only presence of food in the alimentary canal triggers the corresponding neural and hormonal controls.
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