52 - Digestion and absorption of proteins, fats and carbohydrates in the gastrointestinal tract. Absorption of salts, water and vitamins.

sections

digestion and absorption of proteins in GIT

digestion and absorption of fats in GIT

digestion and absorption of fats in small intestines

carbohydrate digestion

absorption of water, salts and vitamins

digestion and absorption of proteins in GIT

• Pepsin digests proteins in the stomach at a pH of 2–3.

• In the small intestine, pancreatic enzymes like trypsin, trypsinogen, carboxypolypeptidase, and elastase break proteins into smaller units.

• Most proteins are broken down into dipeptides and tripeptides.

• Final digestion happens in the enterocytes (intestinal cells) using aminopolypeptidase and dipeptidase.

• These enzymes split peptides into amino acids inside the cells.

• Peptidases in the cytosol complete the breakdown to single amino acids.

• Amino acids are absorbed via Na⁺-driven, H⁺-active transport, or pinocytosis, then enter the blood capillaries.

digestion and absorption of fats in GIT

• Some of the lipid digestion happens in the mouth by lingual lipase and after swallowing

• also in the stomach -gastric lipase. – manily for short chain fatty acids

• long chain fatty acids are broken down by the pancreatic lipase in the small intestine.

digestion and absorption of fats in small intestines

1. emulsification -,by bile acids

2. Increase in surface area, makes easier to break down.

3. pancreatic lipase → digests all TAGs → FFA and glycerol.

4. The end product enter the enterocytes and are released in the cell

5. Here they are again remade into TAG and packaged chylomicrons, which are released in the blood and carried in this way the peripheral tissues.

carbohydrate digestion

• begins in the mouth by salivary a-amylase. --- This enzyme breaks down carbs down partially

• most of the digestion occurs by pancreatic amylase.

• Pancreatic amylase- breaks down the polysaccharide chain into disaccharides, by hydrolysis.

• The small intestine produces lactase, sucrase and maltase, breaks down the disaccharides→ monosaccharides

• The monosaccharides can be absorbed by the enterocytes.

• Glucose – Na+ symport– GLUT2 • GLUT 5 is associated for the transport of fructose.

absorption of water, salts and vitamins

• Water absorption mainly happens in the large intestine by diffusion.

• When chyme is dilute, water is absorbed into the blood by osmosis.

• Sodium (Na⁺) absorption needs ATP (energy).

• Na⁺ helps transport amino acids and monosaccharides.

• Na⁺ moves from chyme into epithelial cells, then to the interstitial fluid and blood.

• Fat-soluble vitamins are absorbed with fats in micelles, then packed into chylomicrons and released into the bloodstream.