carbohydrate ,fat, protein

 🔊CONTENTS

👉Short notes - Carbohydrate 4M

👉 digestion and absorption of carbohydrate 6M

👉 digestion and absorption of protein 6mark

 A. CARBOHYDRATE

Human diet contains three types of carbohydrates:

 1. POLYSACCHARIDES:-

 • Starch (rich in potatoes)

 • Cellulose and pectin, these cannot be digested by the enzymes in the human GIT.

 • Glycogen, here glucose molecules are mostly in long chain

 2. DISACCHARIDES:-

 Two types of disaccharides are available in the diet.

 • Sucrose (Glucose + Fructose), which is called table sugar or cane sugar

 • Lactose (Glucose + Galactose), which is the sugar available in milk.

 3. MONOSACCHARIDES:-

 Monosaccharides consumed in human diet are mostly glucose and fructose.

Other carbohydrates in the diet include:-

 i. Alcohol

 ii. Lactic acid

 iii. Pyruvic acid

 iv. Pectins

 v. Dextrins

 vi. Carbohydrates in meat.

 B. digestion and absorption of carbohydrate:-

 DIGESTION OF CARBOHYDRATES:-

 i. IN THE MOUTH

 Enzymes involved in the digestion of carbohydrates are known as amylolytic enzymes.

 The only amylolytic enzyme present in saliva is the salivary amylase

 ii. IN THE STOMACH

 Gastric juice contains a weak amylase, which plays a minor role in digestion of carbohydrates

 iii. IN THE INTESTINE

 Amylolytic enzymes present in the small intestine are derived from pancreatic juice and succus entericus.

 • Amylolytic Enzyme in Pancreatic Juice:-

 Pancreatic juice contains pancreatic amylase converts all form of starch and dextrins completely into maltose.

 • Amylolytic Enzymes in Succus Entericus:-

 Succus entericus contains disaccharidases i.e. enzymes for splitting disaccharides into monosaccharides. For example: sucrase , maltase, lactase and dextrinase.

 ABSORPTION OF CARBOHYDRATES:-

 Carbohydrates are absorbed from the small intestine mainly as monosaccharides, viz. glucose, galactose and fructose.

 i. ABSORPTION OF GLUCOSE

 • Glucose is transported from the lumen of small intestine into the epithelial cells in the mucus membrane of small intestine, by means of sodium cotransport.

 • From the epithelial cell, glucose is absorbed into the portal vein by facilitated diffusion.

 • From here, it is transported into blood by active transport.

 ii. ABSORPTION OF GALACTOSE

 Galactose is also absorbed from the small intestine same as that of glucose.

 iii. ABSORPTION OF FRUCTOSE

 Fructose is absorbed into blood by means of facilitated diffusion.

 C. digestion and absorption of protein:-

 DIGESTION OF PROTEINS:-

 Enzymes responsible for the digestion of proteins are called proteolytic enzymes.

 i. IN THE MOUTH

 Digestion of protenis does not occur in mouth, since saliva does not contain any proteolytic enzymes.

 ii. IN THE STOMACH

 The only proteolytic enzyme in gastric juice is Pepsin.

 • Pepsin is secreted as inactive pepsinogen. Pepsinogen is converted into pepsin by hydrochloric acid.

 • Pepsin convert proteins into proteoses, peptones and polypeptides. Pepsin also causes curdling and digestion of milk

 iii. IN THE SMALL INTESTINE

Most of the protein are digested in duodenum and jejunum. It is digested by

 a. Protolytic enzyme in pancreatic juice:

 Pancreatic juice contain trypsin, chymotrypsin and carboxypeptidase.

 b. Proteolytic enzyme in succus entericus:

 • It contain dipeptidases, tripeptidases and aminopeptidase

Final product of protein digestion are amino acid which are absorbed into blood from intestine.

ABSORPTION OF PROTEINS:

Proteins are absorbed in the form of amino acid from small intestine.

 • The levo amino acid are actively absorbed by means of sodium cotransport

 • the dextro amino acids are absorbed by means of facilitated diffusion.

 D. DIGESTION OF FAT(LIPIDS):-

 Lipids are digested by lipolytic enzymes.

 i. IN THE MOUTH

 • Saliva contains lingual lipase.

 • It turns triglycerides into fatty acid and 1,2-diacylglycerol.

 ii. IN THE STOMACH

 • Lipolytic enzyme present in gastric juice is Gastric lipase or tributyrase.

 • It breaks triglycerids into fatty acids + Glycerol.

 iii. IN THE INTESTINE

 • almost all lipids are digested in small intestine due to presence of bile salts, pancratic lipolytic enzymes and Intestinal lipase.

 • pancretic lipase is the most important enzyme for digestion of fats.

Other lipolytic enzymes of pancratic juice are :

 a. Cholestrol ester hydrolase.

 b. Phospholipase A

 c. Phospholipase B

 • Intestinal lipase is only lipolytic enzymes present in sucus entericus.

 • Final product are

 a. Fatty acids

 b. Cholesterol

 c. Monoglycerides