Answer the following questions

Zoology

Digestion and Absorption

Evaluation

Answer the following questions

17. Why are villi present in the intestine and not in the stomach?

• The ileal mucosa has numerous vascular projections called villi

• It is involoved in the process of absorption and the cells lining the villi produce numerous microscopic projections called microvilli.

• A brush border appearance increases the surface area enormously.

• Villi are not present in the stomach, because absorption doesnot occur and digestion happens with the help of gastric juices.

18. Bile juice contains no digestive enzymes, yet it is important for digestion. Why?

• The pile contains bile pigments (Bilirubin and biliverdin)

• The pile pigments are broken down products of heamoglobin of dead RBC's

• Bile salts, cholesterol and phospho lipids.

• Bile has no enzyme.

• Bile helps in emulsification of fats.

• Bile salts reduce the surface tension of fat droplets and break them into small globules. Bile also activates lipase to digest lipids.

19. List the chemical changes that starch molecule undergoes from the time it reaches the small intestine.

• Maltose ----^Maltase→ glucose + glucose

• Sucrose ----^Sucrase→ glucose + fructose

• Lactose -----^Lactase→ glucose + galactose

20. How do proteins differ from fats in their energy value and their role in the body?

Protein

1. The caloric value 5.65 Kcal/gram

Q. Physiological fuel value 4 Kcal/ gram

Lipid

1. The caloric value 9.45 Kcal/gram

Q. Physiological fuel value 9 Kcal/ gram

21. Digestive secretions are secreted only when needed. Discuss.

• The saliva is secreted by salivary gland in the mouth

Saliva

• The saliva contains water.

• Electrolytes - Na⁺, K⁺, Cl⁻ , HCo⁻₃

• Salivary amylase (ptyalin)

• Mucus (a glycoprotein)

• Polysaccharides, starch is hydrolyzed by the salivary amylase enzyme into disaccharides (maltose)

Stomach

• The gastric juice contains HCl and proenzymes

• Proenzyme pepsinogen on exposure to HC1 gets converted into active enzyme pepsin.

• The HCl provides an acidic medium (pH=1.8) which is optimum for pepsin, kills bacteria and other harmful organisms and avoids putrification.

• Proteolytic enzyme found in gastric juice of Infants is rennin helps in the digestion of milk protein caseinogen to casein in the presence of calcium.

Small Intestine

• Pancreatic juice:

Enzymes : Trypsinogen, Chymotrypsinogen, Carboxypeptidases, Pancreatic, Amalyse, Pancreatic Lipase and Nucleases.

• Trypsinogen is activated by an enzyme enterokinase, secreated by the intestinal mucosa into active trypsin, which in turn activates the enzyme chymotrypsinogen in the pancreatic juice.

Bile Juice

• The bile contains bile pigment (Bilirubin, and biliverdin) as the break down product of heamoglobin of dead RBC's, Bile salts, Cholesterol and phospholipids. But has no enzymes. 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.

Pancreatic juice action

• Trypsin hydrolyses protein into polypeptides and peptones. While chymotrypsin hydrolyses peptide bond associated with specific amino acid.

Succus entericus

• The secretions of the Brunner's gland along with the secretions of the intestinal glands constitute the intestinal juice or succus entericus.

Enzymes : Maltase, lactase, sucrase (invertase), dipeptidases, lipases, nucleosidases.

Bicarbonate ions from the Pancreas provides an alkaline medium (pH=7.8) for the enzymatic action.

All Macromolecules → Micromolecules

Carbohydrate → Monosaccharides

Protein → Aminoacid

Lipids → Fatty acids and Glycerol

22. Label the given diagram.