CHAPTER 6: STILL WITH THE SOURCES: NOW, THE GASTROINTESTINAL SYSTEM

After food ingestion and the digestion process in the stomach, the intestinal contents move from the duodenum through the rest of the small intestine, while more and more micronutrients are given off by the food. They must be absorbed into the surrounding cells and distributed to all the body tissues. Most absorption takes place by diffusion, so the available surface area and the concentration gradient determine the rate of absorption across the cell membrane. The intestine is specialized to maximize both. Absorption is an essential function for life maintenance. Malabsorption implies defective entrance of a dietary constituent resulting from interference with its digestion or absorption. In small animals, it is typically due to exocrine pancreatic insufficiency, whereas most cases of absorption failure are caused by small intestinal disease. This chapter will try to go deeper in it while devoting also space to the hepatic exchanger.