Protein digestion begins when you first start chewing. There are two enzymes in your saliva called amylase and lipase. They mostly break down carbohydrates and fats. Once a protein source reaches your stomach, hydrochloric acid and enzymes called proteases break it down into smaller chains of amino acids.
1. denaturation by stomach acid and partial digestion by pepsin
2. the pancreas secretes protein-splitting enzymes
3. final digestion occurs within absorptive cells
4. amino acids enter the portal vein and travel to the liver
5. rectum: very little dietary protein in is excreted in feces
