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Ketone bodies are three chemicals that are produced as by-products when fatty acids are broken down for energy.
Contrary to what the name "bodies" may suggest, these are soluble compounds, not particles.
Uses in the heart and brainEdit
Ketone bodies can also be used for energy. Ketone bodies are transported from the liver to other tissues, where acetoacetate and beta-hydroxybutyrate can be reconverted to acetyl-CoA to produce energy.
The heart gets much of its energy from ketone bodies, although it also uses a lot of fatty acids.
The brain gets its energy from ketone bodies when insufficient glucose is available (e.g. when fasting). In the event of low blood glucose, most other tissues have additional energy sources besides ketone bodies (such as fatty acids) but the brain does not. After the diet has been changed to lower blood glucose for 3 days, the brain gets 30% of its energy from ketone bodies. After 40 days, this goes up to 70% (during the initial stages the brain does not burn ketones, since they are an important substrate for lipid synthesis in the brain). The brain retains some need for glucose, because ketone bodies can be broken down for energy only in the mitochondria, and brain cells' long thin axons are too far from mitochondria.
Ketone bodies are produced from acetyl-CoA (see ketogenesis) mainly in the mitochondrial matrix of liver cells when carbohydrates are so scarce that energy must be obtained from breaking down fatty acids.
Acetone is formed from spontaneous decarboxylation of acetoacetate. In a corresponding manner, the levels of acetone are much lower than those of the other two types of ketone bodies. And, unlike the other two, acetone cannot be converted back to acetyl-CoA, so it is excreted in the urine and exhaled (it can be exhaled because it has a high vapor pressure and thus evaporates easily). The exhalation of acetone is responsible for the characteristic "fruity" odour of the breath of persons in ketotic states.
Ketosis and ketoacidosisEdit
Any production of these compounds is called ketogenesis, and this is necessary in small amounts.
But, when excess ketone bodies accumulate, this abnormal (but not necessarily harmful) state is called ketosis.
When even larger amounts of ketone bodies accumulate such that the body's pH is lowered to dangerously acidic levels, this state is called ketoacidosis.
Impact upon pHEdit
See also Edit
- Atkins Nutritionals, Inc. Lipolysis and Ketosis
- eMedicine emerg/135 - Diabetic Ketoacidosis
- Fat metabolism at unisanet.unisa.edu.au
- Breath acetone is a reliable indicator of ketosis in adults consuming ketogenic meals, American Journal of Clinical Nutrition.
- NHS Direct Online Health Encyclopaedia, Ketosis
- BioCarta Pathways Formation of Ketone Bodiesde:Ketokörper
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