Digestion of lipids primarily begins in the stomach where fat is mixed and broken into droplets that have a tendency to float on the contents of the stomach before passing into the small intestine. Bile produced from cholesterol by the liver and stored in the gall bladder is released into the small intestine further breaks the fat into small droplets. Once is this form pancreatic lipases break the fat droplet triglycerides into 2 fatty acids and one monoglyceride. Free fatty acids, glycerol and monoglycerides cling together in round balls called micelles. Short fatty acids can move directly across into the bloodstream whereas larger chained fatty acids require assistance. Triglycerides combine with cholesterol, phospholipids and protein to form chylomicrons which are absorbed and can travel safely in the watery blood.
LDL/HDL: In addition to chylomicrons, the body used three other lipoproteins to transport lipids in the blood stream.
- Very low density lipoproteins VLDL: carry triglycerides and other lipids made in the liver to cells.
- Low density lipoproteins (LDL): made from VLDL transport cholesterol and other lipids to cells
- High density lipoproteins (HDL): carry cholesterol away from the liver for disposal
The functions of LDL and HDL define why LDL is known as bad cholesterol and HDL is known as good cholesterol. Although both lipoproteins carry cholesterol, HDL is involved in removing cholesterol whereas LDL is involved in transporting from the liver to tissue. High levels of LDL are associated with an increased risk of heart disease.