Catabolism

 ( Metabolism ) 

Catabolism () is the set of Metabolism pathways that breaks down into smaller units that are either oxidized to release energy or used in other anabolic reactions. Catabolism breaks down large molecules (such as , , , and ) into smaller units (such as , , , and , respectively). Catabolism is the breaking-down aspect of metabolism, whereas anabolism is the building-up aspect.

Cells use the monomers released from breaking down polymers to either construct new polymer molecules or degrade the monomers further to simple waste products, releasing energy. Cellular wastes include lactic acid, acetic acid, carbon dioxide, ammonia, and urea. The formation of these wastes is usually an oxidation process involving a release of chemical free energy, some of which is lost as heat, but the rest of which is used to drive the synthesis of adenosine triphosphate (ATP). This molecule acts as a way for the cell to transfer the energy released by catabolism to the energy-requiring reactions that make up anabolism.

Catabolism is a destructive metabolism and anabolism is a constructive metabolism. Catabolism, therefore, provides the chemical energy necessary for the maintenance and growth of cells. Examples of catabolic processes include glycolysis, the citric acid cycle, the breakdown of muscle protein in order to use amino acids as substrates for gluconeogenesis, the breakdown of fat in adipose tissue to , and oxidative deamination of neurotransmitters by monoamine oxidase.

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Catabolic hormones There are many signals that control catabolism. Most of the known signals are and the molecules involved in metabolism itself. have traditionally classified many of the hormones as anabolic or catabolic, depending on which part of metabolism they stimulate. The so-called classic catabolic hormones known since the early 20th century are cortisol, glucagon, and adrenaline (and other ). In recent decades, many more hormones with at least some catabolic effects have been discovered, including , orexin (known as hypocretin), and melatonin.

Cortisol	Released from the adrenal gland in response to stress; its main role is to increase blood glucose levels by gluconeogenesis.
Glucagon	Released from alpha cells in the pancreas either when starving or when the body needs to generate additional energy; it stimulates the breakdown of glycogen in the liver to increase blood glucose levels; its effect is the opposite of insulin; glucagon and insulin are a part of a negative-feedback system that stabilizes blood glucose levels.
Adrenaline	Released in response to the activation of the sympathetic nervous system; increases heart rate and heart contractility, Vasoconstriction blood vessels, is a bronchodilator that opens (dilates) the Bronchus of the to increase air volume and oxygen supply in the lungs, and stimulates gluconeogenesis.

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Etymology The word catabolism is from Neo-Latin, which got the roots from Ancient Greek: κάτω kato, "downward" and βάλλειν ballein, "to throw".

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See also

• Autophagy
• Dehydration synthesis
• Hydrolysis
• Nocturnal post absorptive catabolism
• Psilacetin § Pharmacology
• Sarcopenia

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