2) VLDLs
10% protein, 50% triglycerides, 20% phospholipid, 20% cholesterol. Form in hepatocytes Contain mainly endogenous (made in the body) lipids. Transport triglycerides synthesized in hepatocytes to adipocytes for storage. As triglycerides are deposited in adipose cells, VLDLs are converted to LDLs
3) LDLs
25% protein, 5% triglycerides, 20% phospholipids, 50% cholesterol Carry about 75% of the cholesterol in blood and deliver it to cells throughout the body for use in repair of cell membranes and synthesis of steroid hormones and bile salts. Within the cell, the LDL is broken down and the cholesterol is released to serve the cells needs. Once the cell has sufficient cholesterol for its needs, a negative feedback system inhibits the synthesis of new LDL receptors. In excess numbers, LDLs also deposit cholesterol in and around smooth muscle fibres in arteries, forming fatty plaques. High-fat diet increases the production of VLDLs which elevate the LDL levels.
4) HDLs
40-45% protein, 5-10% triglycerides, 30% phospholipids, 20% cholesterol. Remove excess cholesterol from body cells and the blood and transport it to the liver for elimination.
The Fate of Lipids
Lipids like carbohydrates may be oxidized to produce ATP. If there is no immediate need to use lipids in this way, they are stored in adipose tissue (fat deposits) throughout the body. A few lipids are used as structural molecules or to synthesis other essential substances.
Triglyceride Storage
A major function of adipose tissue is to remove triglycerides from chylomicrons and VLDLs and store them until they are needed for ATP production in other parts of the body. Triglycerides stored in adipose tissue constitute 98% of all body energy reserves. They are stored more readily than glycogen. Triglycerides in adipose tissue are continually broken down and resynthesized.
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