Absorption and Digestion Flashcards
Carbohydrates
Digestion of carbohydrates is due to salivary glands and exocrine pancreas
Alpha Amylase
Salivary alpha amylase has an optimum pH of 6.6-6.8 and is inactivated by the stomach pH
Pancreatic alpha amylase does most of the protein digestion
Attacks the 1,4 glycosidic links
Endoglycosidases only attack the middle of the chain
Di, tri and oligosaccharides are broken down at the brush border by disaccharidases
The products are therefore mainly glucose with small amounts of fructose and galatose
Fructose is absorbed by carrier mediated diffusion
Glucose and galactose absorption
Via the apical surface, Na and glucose are actively co transported into the enterocyte by SGLT-1
Via the basolateral surface the glucose is removed via GLUT-2
K+ in and Na+ out via and NaK ATP pump
Lipids
Lingual lipase in the mouth and stomach
Pancreatic lipase in the SI which requires phospholipids and bile acids from bile to work
The products of fat digestion are free fatty acids, 2 monoacylglycerol, 1 monoacylglycerol and glycerol
Bile acids and phospholipids break down the lipid molecules into micelles
Micelles transport the fatty acids and glycerol to the surface of the enterocyte
Micelles breakdown as only freely dissolved monoacylglycerols and fatty acids can be absorbed. They diffuse in.
Once inside the enterocyte, they are resynthesiseD into TAG
TAG +soluble vitamins +cholestrol form chylomicrons and are released at the basolateral surface by exocytosis
Chylomicron with lipoprotein lipase form chylomicron remenants which go to the liver
Chylomicron releases fatty acid to tissues secreted to lymph to blood via thoracic duct
Proteins
All proteases attack peptide bonds
Endopeptidases attack the middle and are secreted by the stomach and pancreas
Exopeptidases attack the end and are secreted by the pancreas and small intestine
They are secreted as inactive precursors known as zymogens
Protein digestion begins in the stomach via the endopeptidase PEPSIN
Pepsin attacks all proteins except mucin and keratin
In the pancreas, three endopeptidases are produced and secreted as zymogens into the small intestine
Trypsinogen
Chymotrypsinogen
PRO-ELASTASE
Exopeptidases
Carboxypeptidases secreted by the pancreas as zymogens
Aminopeptidases secreted by the small intestine glands
Amino acids are absorbed by a sodium dependent active transport system
