Figure 1. Formation of a triglyceride molecule.

Figure 2. Names and structures of some common fatty acids.

Figure 3. Digestion and absorption of dietary lipids. (1) Dietary lipid leaves the stomach and enters the upper region of the small intestine where bile acids, released from the gallbladder,surround and coat droplets of fat to form emulsion particles. The emulsion particles provide the surface area for the pancreatic enzymes to degrade the dietary lipids. (2) Phospholipase A₂ (PLA₂) breaks down each phospholipid (PL)into a free fatty acid (FFA) and a lysophospholipid (LPL). (3) Pancreatic lipase (PLps) converts triglyceride (TG) into a monoglyceride (MG) and two free fatty acids. (4) Cholesterol esterase (CEtrs) splits cholesterol ester (CE) into free cholesterol and a free fatty acid. (5) The products of lipid digestion coalesce with bile acids into mixed micelles. (6) The mixed micelles move close to the mucosal cell surface, where the lipids diffuse down a concentration gradient into the mucosal cells. (7) Bile acids are not absorbed. (8) Short- and medium-chain fatty acids move immediately into the portal circulation where they are transported in the blood bound to albumin. (9) To maintain the concentration gradient necessary for lipid diffusion, the breakdown products of lipid digestion are resynthesized into their parent lipids. (10) The lipids are combined with apolipoproteins, synthesized in the mucosal cells, to form chylomicrons. (11) Chylomicrons leave the mucosal cell via the lymphatic vessels.

Figure 4. Structure of a plasma lipoprotein.

Figure 5. Desaturation and elongation of polyunsaturated fatty acids.

Figure 6. Synthesis and degradation of triacylglycerol.