Lipolysis (pron.: //) is the breakdown of lipids and involves hydrolysis of triglycerides into free fatty acids, followed by degradation into acetyl units by beta oxidation. It produces ketones, which when produced in large quantities are described as causing ketosis. These can then be used by the body for energy. Lipolysis testing strips are used to detect ketosis, primarily in diabetic ketoacidosis.
The following hormones induce lipolysis: epinephrine, norepinephrine, ghrelin, growth hormone, testosterone, and cortisol (In which cortisol assist in releasing body fat and carbohydrates for a source of energy) These trigger 7TM receptors (G protein-coupled receptors), which activate adenylate cyclase. This results in increased production of cAMP, which activates protein kinase A, which subsequently activates lipases found in adipose tissue.
Triglycerides are transported through the blood to appropriate tissues (adipose, muscle, etc.) by lipoproteins such as VLDL (Very-Low-Density-Lipoproteins). Triglycerides present on the VLDL undergo lipolysis by the cellular lipases of target tissues, which yields glycerol and free fatty acids. Free fatty acids released into the blood are then available for cellular uptake. Free fatty acids not immediately taken up by cells may bind to albumin for transport to surrounding tissues that require energy. Serum albumin is the major carrier of free fatty acids in the blood. The glycerol also enters the bloodstream and is absorbed by the liver or kidney where it is converted to glycerol 3-phosphate by the enzyme glycerol kinase. Hepatic glycerol 3-phosphate is converted mostly into dihydroxyacetonephosphate (DHAP) and then glyceraldehyde 3-phosphate (GA3P) to rejoin the glycolysis and gluconeogenesis pathway.
While lipolysis is triglyceride hydrolysis (the process by which triglycerides are broken down), esterification is the process by which triglycerides are formed. Esterification and lipolysis are, in essence, reversals of one another.
- Michael W King, PhD. "Oxidation of Fatty Acids". themedicalbiochemistrypage.org, LLC. Retrieved 9 April 2012.
- Tom Brody, Nutritional Biochemistry, (Academic Press, 2nd edition 1999), 215-216. ISBN 0121348369
- Baldwin, Kenneth David Sutherland; Brooks, George H.; Fahey, Thomas D. (2005). Exercise physiology: human bioenergetics and its applications. New York: McGraw-Hill. ISBN 0-07-255642-0.