The Small Intestine
The bulk of absorption occurs in the small intestine (SI). This is made difficult by the need to maintain a barrier against toxins and pathogens. The breakdown of nutrients into small constituents facilitates this.
The duodenum
The jejeunum
The Ileum
The terminal ileum is the site of vitamin B12/Intrinsic Factor absorption and also the site of bile salt recycling.
The crypts act as germinal centres and as sites for ion and water secretion.
Digestive Secretions
Levels of pancreatic and gall bladder secretion must be closely matched to digestive requirements, necessitating sophisticated communication.
Protein Digestion
Carbohydrate Digestion
Lipid Digestion
Lipids are emulsified by bile salts and digested by pancreatic lipase in the small intestine.
Intrisicn factors is made by parietal cells in the stomach. It binds to Vitamin B12, which is cotransported in the terminal ileum. Destruction of parietal cells causes lack of intrisic factor and malabsorption of B12, leading to pernicious anemia.