2- Digestion of Carbohydrates and Proteins

Dietary disaccharides

Don't need alpha-amylase to be digested, need brush border enzymes instead in order to become monosaccharides!

Absorption of monosaccharides

Then they are absorbed as glucose, galactose, and fructose!

Fructose absorption

Absorbed across apical membrane by passive facilitated diffusion GLUT5 and moves across basolateral membrane by passive facilitated diffusion GLUT2.

PepT1

Moves di, tri, and tetrapeptides across apical membrane into enterocytes and is responsible for absorption of dietary di and tripeptides from SI lumen.

Cholesteryl Ester Transfer Protein

Transfers cholesterol esters to other particles.

Hepatic Lipase

Degrades TGs in IDL.

Hormone-Sensitive Lipase

Degrades TGs in adipocytes.

Lecithin-Cholesterol Acyltransferase

Esterification of plasma cholesterol.

Lipoprotein Lipase

Degrades TGs in chylomicrons.

Pancreatic Lipase

Degrades TGs in SI.

SI Brush-Border Enzymes

Include Enterokinase, Disaccharidases, and Aminopeptidases.

Amino Acids crossing basolateral membrane

Facilitated or Simple Diffusion.

Brush-Border Oligosaccharidases

Include Lactase, Maltase (glucoamylase), Sucrase, and Isomaltase.

Lactase

Catalyzes Lactose to Glucose + Galactose.

Maltase (glucoamylase)

Catalyzes Maltose to Glucose.

Sucrase

Catalyzes Sucrose to Glucose + Fructose.

Alpha-Dextrinase

Catalyzes alpha-limit dextrins to Glucose.

Pancreatic Lipase breakdown

Breaks down TG's into mono-glycerides and free FA's.

Hartnup Disease

Issue with reabsorption of all neutral amino acids; PepT1 helps compensate for the reduced amino acid delivery.

Micelles

Allow for fat absorption and are formed by bile salts.

Endopeptidases

Cleave peptide bonds inside polypeptide.

Exopeptidases

Cleave peptide bonds from the ends of the polypeptide.

Proenzyme Activation

Trypsinogen is activated by Enteropeptidase & Trypsin to Trypsin (Endopeptidase).

Digestion and absorption of lipids

Involves emulsification by bile salts, hydrolysis by lipase, and formation of micelles for absorption.