Your body must break down the fatty molecules known as lipids for many biologic processes including absorption, transport across cell membranes and the generation of energy. Lipid breakdown takes place throughout your body and is accomplished by the action of various enzymes.
Lipids are a class of molecules that include triglycerides, sterols, phospholipids and other complex compounds, the authors of "Hole's Human Anatomy and Physiology" explain. Some 95 percent of dietary lipids and lipids in your body are triglycerides. A triglyceride is composed of a glycerol molecule to which three different fatty acids are attached.
Lipases are a category of enzymes produced in different organs that break down triglycerides. According to the book "Advanced Nutrition and Human Metabolism," lipases break down triglycerides by chemically removing the fatty acids from the glycerol portion of the molecule. The products of complete triglyceride breakdown include three fatty acids and a glycerol molecule.
Your body must break down triglycerides from your diet so they can be absorbed into the intestinal cells, "Advanced Nutrition and Human Metabolism" explains. Triglyceride digestion is accomplished primarily by pancreatic lipase. This enzyme is produced in the pancreas, then exported to the small intestine, where it interacts with dietary triglycerides.
Triglycerides are often packaged into large molecules, called lipoproteins, for transport throughout the body, "Advanced Nutrition and Human Metabolism" notes. Chylomicrons and very-low-density lipoproteins are examples of lipoproteins that transport triglycerides. The triglycerides in lipoproteins are broken down by lipoprotein lipase, an enzyme associated with the blood vessels in adipose (fatty) and muscle tissue. The action of lipoprotein lipase removes free fatty acids from lipoproteins and allows them to enter cells to be used for energy or other processes.
Your body primarily stores triglycerides in adipose tissue, though it does also store some within muscle cells. According to "Hole's Human Anatomy and Physiology," hormones such as epinephrine mediate the breakdown of stored triglyceride. Epinephrine activates hormone-sensitive lipase, an enzyme that removes the fatty acids from the triglyceride molecule in a manner similar to pancreatic and lipoprotein lipases. Your body will use the free fatty acids generated by hormone-sensitive lipase as an energy source.
- "Advanced Nutrition and Human Metabolism (5th Edition)"; S.S. Gropper, J.L. Smith, J.L. Groff; 2009
- "Hole's Human Anatomy and Physiology (11th Edition)"; David N. Shier, Jackie L. Butler, Ricki Lewis; 2007