Chylomicron

Chylomicrons (from the Greek χυλός, chylos, meaning juice (of plants or animals), and micron, meaning small particle) are lipoprotein particles that consist of triglycerides (85–92%), phospholipids (6–12%), cholesterol (1–3%), and proteins (1–2%). Due to their density relative to lipoproteins, they are also commonly known as ultra low density lipoproteins (ULDL) in modern usage. They transport dietary lipids from the intestines to other locations in the body. ULDLs are one of the five major groups of lipoproteins (sorted by density) that enable fats and cholesterol to move within the water-based solution of the bloodstream. A protein specific to chylomicrons is ApoB48. Chylomicrons (from the Greek χυλός, chylos, meaning juice (of plants or animals), and micron, meaning small particle) are lipoprotein particles that consist of triglycerides (85–92%), phospholipids (6–12%), cholesterol (1–3%), and proteins (1–2%). Due to their density relative to lipoproteins, they are also commonly known as ultra low density lipoproteins (ULDL) in modern usage. They transport dietary lipids from the intestines to other locations in the body. ULDLs are one of the five major groups of lipoproteins (sorted by density) that enable fats and cholesterol to move within the water-based solution of the bloodstream. A protein specific to chylomicrons is ApoB48. There is an inverse relationship in the density and size of lipoprotein particles: the larger particles (higher ratio of fat molecules inside compared with the outer emulsifying protein molecules in the shell) and fats are always lower density than either protein or water molecules, i.e. fats float in water. ULDLs, being the least dense, are the largest and only lipoprotein particles that can sometimes (if large enough, at close to about 1,000 microns or more) be seen using only a light microscope, at maximum magnification. All the other classes are submicroscopic, one of the reasons these particles were long difficult to identify and better understand. Chylomicrons transport lipids absorbed from the intestine to adipose, cardiac, and skeletal muscle tissue, where their triglyceride components are hydrolyzed by the activity of the lipoprotein lipase, allowing the released free fatty acids to be absorbed by the tissues. When a large portion of the triacylglycerol core have been hydrolyzed, chylomicron remnants are formed and are taken up by the liver, thereby also transferring dietary fat to the liver. Chylomicrons are formed in the endoplasmic reticulum in the absorptive cells (enterocytes) of the small intestine. The villi, lined with the microvilli of the brush border, provide a lot of surface area for absorption. Newly formed chylomicrons are secreted through the basolateral membrane into the lacteals, where they join lymph to become chyle. The lymphatic vessels carry the chyle to the venous return of the systemic circulation. From there the chylomicrons supply the tissue with fat absorbed from the diet. Thus, unlike the saccharides and amino acids that digestion liberates from the carbohydrates and proteins of the diet (respectively), the lipids from the diet bypass the hepatic portal system, meaning the liver does not get 'first crack' at them.