Carbohydrates

• In typical omnivore, most are polysaccharides, starch and cellulose with some monosaccharides and disaccharides

• Mouth: starch digestion by salivary amylase

• Additional starch digestion by pancreatic amylase

• Monosaccharides transported across intestinal epithelium into the blood

Proteins

• Pepsin in the stomach

• Pancreas secretes trypsin and chymotrypsin

  • Pancreas secretes them as inactive precursors

  • Activated in small intestine

• Small intestine enzymes complete digestion of proteins into amino acids

• Transported into intestinal cells and into bloodstream

Lipids

• Most in the form of triglycerides

• Digestion entirely in small intestine

• Pancreatic lipase

• Phospholipids and bile salts emulsify fat into small droplets with increased surface area for digestion

• Bile salts form micelles allowing lipids to diffuse into intestinal cells

• Triglycerides reform inside intestinal cells

• Aggregate into chylomicrons released by exocytosis to pass into lacteals

• Will enter into general blood circulation

Vitamins, Minerals, and Water

• Do not require digestion

• Absorbed in complete form

• Fat-soluble vitamins follow pathway for fat absorption

• Small amounts of water absorbed in stomach but most in small intestine