The Uptake of Lipids into the Intestinal Mucosa

Abstract

Fats, proteins, and complex carbohydrates represent the major sources of calories in the typical diet found in the Western world. During digestion within the proximal small intestine, proteins and carbohydrates are broken down into simpler peptides and saccharides that are very polar and so are soluble in the aqueous environment of the intestinal contents. Because of the high degree of interaction between these polar products and the water phase, carrier-mediated and energy-linked transport processes are required to bring about net transfer of these molecules from the intestinal lumen into the cytosolic compartment of the columnar absorptive cell of the jejunum and ileum. ^{(1, 2)} In contrast, the digestion of complex dietary lipids releases products that are still very unpolar and, therefore, have very low aqueous solubilities. Such molecules are, however, readily absorbed across the microvillus membrane of the intestinal cell by passive mechanisms. This chapter reviews the unique biochemical and physiological mechanisms that interact to bring about the absorption of dietary lipids from the external environment, i.e., the contents of the intestinal lumen, into the body, i.e., the cytosolic compartment of the columnar epithelial cell of the small intestine. ⁽³⁾