Question

Describe the following processes in the body

(a) Coagulation of milk in the alimentary canal. (b) Digestion of fats in the intestine. (c) Digestion of starch in the alimentary canal. (d) Role of bile salts in the digestion and absorption of fats.

Answer 1

• Milk after reaching the stomach,is acted upon by the proteolytic enzyme pepsin. Pepsin hydrolyzes the milk protein, Casein (soluble) into insoluble paracasein which precipitates as calcium paracaseinate to form semi solid curd. This is known as coagulation of milk. Rennin promotes the coagulation process in the stomach of infants.
• The digestion of fats begins in the small intestine. Bile juice secreted by the liver emulsifies the fat into smaller fat globules so as to increase the surface area for the lipase to act. Pancreatic lipase then acts on the globules and convert it into di- and monoglycerides. The enzymes in the succus entericus act on the end product of the above reaction to form the simple absorbable form. Lipases present in the succus entericus converts the di- and monoglycerides into fatty acids and glycerol.
• The polysaccharides(starch) is digested by various enzymes produced in the digestive tract. The polysaccharides are broken down to oligosaccharides and disaccharides which are further digested to form monosaccharides which are simple sugars.

Digestion of Polysaccharides.

Action of Saliva Starch −→−−−−−−−AmylaseSalivary→AmylaseSalivary Maltose ++ Isomaltose +α+α - Dextrins

Action of Pancreatic Juice

Starch −→−−−−−−−−−α−AmylasePancreatic→α−AmylasePancreatic Maltose ++ Isomaltose +α+α-Dextrins

Digestion of Disaccharides

Action of intestinal juice

Maltose −→−−−−−−−Maltase→Maltase Glucose ++ Glucose

Isomaltose −→−−−−−−−−−Isomaltase→Isomaltase Glucose ++ Glucose

Dextrins −→−−−−−−−−−−−α−Dextrinase→α−Dextrinase Glucose

These simple sugars are then absorbed in jejunum and ileum region of small intestine.

• Bile salts help in the emulsification of the fats i.e. breaking down of the fat into very small micelles so as to increase the surface area for the lipase to act and thus aiding in the digestion of fats. Fatty acids and glycerol being insoluble, cannot be absorbed into the blood. They are first turned into small droplets called micelles with the help of bile salts which move into intestinal mucosa. They are re-formed into very small protein coated fat globules called chylomicrons which are transported into the lacteals in the villi. Lacteals ultimately release the absorbed substances into the blood stream.