Digestion

Digestive enzymes

Mouth

carbohydrate digestion

salivary amylase - breaks down carbohydrates to simpler sugars (disaccharides and trisaccharides)

Stomach

protein digestion

pepsin - breaks down proteins to polypeptides(pepsinogen is secreted and coverted to pepsin by HCl)

HCl - disrupts cell membranes in food, activates pepsin

Small intestine

cardohydrate digestion

pancreatic amylase (from pancreas) - breaks down carbohydrates to simpler sugars (disaccharides and trisaccharides)maltase (from small intestine) - breaks down maltose (a disaccharide) to two glucose molecules

sucrase (from small intestine) - breaks down sucrose (a disaccharide) to glucose and fructose

lactase (from small intestine) - breakdown lactose (a disaccharide) to glucose and galactose

protein digestion

pancreatic proteinases (from pancreas: chymotrypsin, trypsin, carboxypeptidase, elastase) - break down proteins and polypeptides to short chain peptides

pancreatic peptidase (from pancreas) - breaks down dipeptides and tripeptides to amino acids

peptidase (from small intestine) - breaks down dipeptides and tripeptides to amino acids

fat digestion

bile (from liver) - emulsifies fats

pancreatic lipase (from pancreas) - breaks down triglycerides to fatty acids and monoglycerides

Absorption

• simple sugars are absorbed through intestinal epithelium by facilitated diffusion and cotransport
• amino acids are absorbed through the intestinal epithelium by facilitated diffusion and cotransport
• fatty acids and monoglycerides bind to bile salts to form micelles
• the lipids diffuse into the intestinal epithelium where they are rejoined as triglycerides and coated with protein to form chylomicrons
• the chylomicrons enter the intestinal lacteals and lymphatics

© David G. Ward, Ph.D.  Last modified by wardd 23 May, 2006