After lipids are digested, they are transported by lipoproteins throughout the body, supplying cells with fats they need to carry on activities that foster normal growth, reproduction and cell function. There are four different lipoproteins, each with a specific "job" to do.
Chylomicrons
Chylomicrons are the largest and most dense lipoprotein. Chylomicrons enter the lymphatic system and travel throughout the body, breaking down and getting smaller as triglycerides are detached from the chylomicron and distributed to cells and adipose sites. Most matter in chylomicrons is used during this process, and the remaining matter in the chylomicron returns to the liver and is recycled as more triglyceride or is inserted into another lipoprotein.
Very Low-Density Lipoproteins
Very low-density lipoproteins (VLDL) travel throughout the body. VLDLs have a smaller concentration of fat to protein at the beginning, with more protein than fat. However, as they travel throughout the body and give off matter, the concentration of cholesterol to protein increases, and they essentially become low-density lipoproteins (LDL) once they increase their concentration of fat to protein enough.
Low-Density Lipoprotein
Low-density lipoproteins, or LDLs, transport cholesterol to replenish cell cholesterol supply. LDLs are then lysed in the liver and secreted into the gallbladder and the intestinal system for waste. Excess LDLs in the bloodstream may break down and release cholesterol into bloodstream, causing plaquing of the arteries. A high ratio of LDLs to HDLs is more than 4 to 1, while a normal ratio is around 3 to 1.
High-Density Lipoproteins
High-density lipoproteins (HDLs) transport excess cholesterol out of the bloodstream and bring it into liver, where it is destroyed or recycled. HDLs are seen as "healthy" lipoproteins because of their "job" of clearing cholesterol out of the bloodstream.
Lipoprotein Structure
A typical lipoprotein contains triglycerides and cholesterol on the inside, surrounded by phospholipids, with proteins covering the outside.
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