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Chylomicrons


Chylomicrons (from the Greek chylo, meaning juice or milky fluid, and micron, meaning small particle) are lipoprotein particles that consist of triglycerides (85–92%), phospholipids (6–12%), cholesterol (1–3%), and proteins (1–2%). They transport dietary lipids from the intestines to other locations in the body. Chylomicrons are one of the five major groups of lipoproteins: chylomicrons (a.k.a. ultra low-density lipoprotein), very low-density lipoprotein, intermediate-density lipoprotein, low-density lipoprotein, high-density lipoprotein, that enable fats and cholesterol to move within the water-based solution of the bloodstream.

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, hereby transferring dietary fat also 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.


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