Lipolysis is the breakdown of lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...

s and involves the hydrolysis of triglycerides into free fatty acids followed by further degradation into acetyl units by beta oxidation
Beta oxidation
Beta oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Citric Acid cycle....

. The process produces Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...

s, which are found in large quantities in ketosis
Ketosis is a state of elevated levels of ketone bodies in the body. It is almost always generalized throughout the body, with hyperketonemia, that is, an elevated level of ketone bodies in the blood. Ketone bodies are formed by ketogenesis when the liver glycogen stores are depleted...

, a metabolic state that occurs when the liver converts fat into fatty acids and ketone bodies, which can be used by the body for energy. Lipolysis testing strips such as Ketostix are used to recognize ketosis.

The following hormones induce lipolysis: epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...

, norepinephrine
Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...

, glucagon
Glucagon, a hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is...

, growth hormone
Growth hormone
Growth hormone is a peptide hormone that stimulates growth, cell reproduction and regeneration in humans and other animals. Growth hormone is a 191-amino acid, single-chain polypeptide that is synthesized, stored, and secreted by the somatotroph cells within the lateral wings of the anterior...

, testosterone
Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...

, and cortisol
Cortisol is a steroid hormone, more specifically a glucocorticoid, produced by the adrenal gland. It is released in response to stress and a low level of blood glucocorticoids. Its primary functions are to increase blood sugar through gluconeogenesis; suppress the immune system; and aid in fat,...

 (although cortisol's actions are still unclear). These trigger 7TM receptors (G protein-coupled receptors), which activate adenylate cyclase
Adenylate cyclase
Adenylate cyclase is part of the G protein signalling cascade, which transmits chemical signals from outside the cell across the membrane to the inside of the cell ....

. This results in increased production of cAMP
Cyclic adenosine monophosphate
Cyclic adenosine monophosphate is a second messenger important in many biological processes...

, which activates protein kinase A
CAMP-dependent protein kinase
In cell biology, Protein kinase A refers to a family of enzymes whose activity is dependent on cellular levels of cyclic AMP . PKA is also known as cAMP-dependent protein kinase...

, which subsequently activates lipase
A lipase is an enzyme that catalyzes the formation or cleavage of fats . Lipases are a subclass of the esterases.Lipases perform essential roles in the digestion, transport and processing of dietary lipids in most, if not all, living organisms...

s found in adipose tissue
Adipose tissue
In histology, adipose tissue or body fat or fat depot or just fat is loose connective tissue composed of adipocytes. It is technically composed of roughly only 80% fat; fat in its solitary state exists in the liver and muscles. Adipose tissue is derived from lipoblasts...


Triglycerides are transported through the blood to appropriate tissues (adipose, muscle
Muscle is a contractile tissue of animals and is derived from the mesodermal layer of embryonic germ cells. Muscle cells contain contractile filaments that move past each other and change the size of the cell. They are classified as skeletal, cardiac, or smooth muscles. Their function is to...

, etc.) by lipoprotein
A lipoprotein is a biochemical assembly that contains both proteins and lipids water-bound to the proteins. Many enzymes, transporters, structural proteins, antigens, adhesins, and toxins are lipoproteins...

s such as chylomicrons. Triglycerides present on the chylomicrons undergo lipolysis by the cellular lipases of target tissues, which yields glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...

 and free fatty acid
Fatty acid
In chemistry, especially biochemistry, a fatty acid is a carboxylic acid with a long unbranched aliphatic tail , which is either saturated or unsaturated. Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28. Fatty acids are usually derived from...

s. 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
Serum albumin
Serum albumin, often referred to simply as albumin is a protein that in humans is encoded by the ALB gene.Serum albumin is the most abundant plasma protein in mammals. Albumin is essential for maintaining the osmotic pressure needed for proper distribution of body fluids between intravascular...

 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
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...

 or kidney
The kidneys, organs with several functions, serve essential regulatory roles in most animals, including vertebrates and some invertebrates. They are essential in the urinary system and also serve homeostatic functions such as the regulation of electrolytes, maintenance of acid–base balance, and...

 where it is converted to glycerol 3-phosphate
Glycerol 3-phosphate
Glycerol 3-phosphate is an organophosphate derived from the reaction catalysed by glycerol kinase where ATP + glycerol ADP + sn-glycerol 3-phosphate. It is a component of glycerophospholipids. It should not be confused with the similarly named glycerate 3-phosphate or glyceraldehyde 3-phosphate...

 by the enzyme glycerol kinase
Glycerol kinase
Glycerol kinase is a phosphotransferase enzyme involved in triglycerides and glycerophospholipids synthesis.Glycerol kinase catalyzes the transfer of a phosphate from ATP to glycerol thus forming glycerol phosphate . Adipocytes lack glycerol kinase so they cannot metabolize the glycerol produced...

. Hepatic glycerol 3-phosphate is converted mostly into dihydroxyacetonephosphate
Dihydroxyacetone phosphate is a biochemical compound involved in many reactions, from the Calvin cycle in plants to the ether-lipid biosynthesis process in Leishmania mexicana. Its major biochemical role is in the glycolysis metabolic pathway...

 (DHAP) and then glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate
Glyceraldehyde 3-phosphate, also known as triose phosphate or 3-phosphoglyceraldehyde and abbreviated as G3P, GADP, GAP, TP, GALP or PGAL, is a chemical compound that occurs as an intermediate in several central metabolic pathways of all organisms...

 (GA3P) to rejoin the glycolysis
Glycolysis is the metabolic pathway that converts glucose C6H12O6, into pyruvate, CH3COCOO− + H+...

 and gluconeogenesis
Gluconeogenesis is a metabolic pathway that results in the generation of glucose from non-carbohydrate carbon substrates such as lactate, glycerol, and glucogenic amino acids....


While lipolysis is triglyceride hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...

 (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.

Lipolysis during stress occurs in the fat cells, which, in turn, increases cholestrol during chronic enduring stress.
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