Editing Lipoprotein (section)

====Exogenous pathway====
[[File:Lipoprotein metabolism.png|500px|thumbnail|right|Simplified flowchart showing the essentials of lipoprotein metabolism.]]

[[Bile]] emulsifies fats contained in the [[chyme]], then [[pancreatic lipase]] cleaves triglyceride molecules into two fatty acids and one 2-monoacylglycerol. [[Enterocyte]]s readily absorb the small molecules from the chymus. Inside of the enterocytes, fatty acids and [[monoacylglyceride]]s are transformed again into triglycerides. Then these lipids are assembled with [[apolipoprotein B-48]] into ''nascent [[chylomicron]]s''. These particles are then secreted into the [[lacteal]]s in a process that depends heavily on apolipoprotein B-48. As they circulate through the [[lymphatic vessels]], nascent chylomicrons bypass the liver circulation and are drained via the [[thoracic duct]] into the bloodstream.

In the blood stream, ''nascent chylomicron particles'' interact with HDL particles, resulting in HDL donation of [[apolipoprotein C-II]] and [[apolipoprotein E]] to the nascent chylomicron. The chylomicron at this stage is then considered mature. Via apolipoprotein C-II, mature chylomicrons activate [[lipoprotein lipase]] (LPL), an enzyme on [[endothelial cell]]s lining the blood vessels. LPL catalyzes the [[hydrolysis]] of triglycerides that ultimately releases glycerol and [[fatty acid]]s from the chylomicrons. Glycerol and fatty acids can then be absorbed in peripheral tissues, especially [[Adipose tissue|adipose]] and [[Muscle tissue|muscle]], for energy and storage.

The hydrolyzed chylomicrons are now called ''chylomicron remnants''. The chylomicron remnants continue circulating the bloodstream until they interact via apolipoprotein E with chylomicron remnant receptors, found chiefly in the liver. This interaction causes the [[endocytosis]] of the chylomicron remnants, which are subsequently hydrolyzed within [[lysosome]]s. Lysosomal [[hydrolysis]] releases glycerol and fatty acids into the cell, which can be used for energy or stored for later use.