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Information about Ketone Bodies



Ketone bodies are three water soluble compounds that are produced as by-products when fatty acids are broken down for energy. They are used as a source of energy in the heart and brain. In the brain, they are a vital source in fasting.

The three ketone bodies are acetoacetate, beta-hydroxybutyrate and acetone, although beta-hydroxybutyrate is not technically a ketone but a carboxylic acid.

Uses in the heart and brain

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, via the Krebs cycle.

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 4 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.

Production

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 ketoacidosis

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 pH

Both acetoacetate and beta-hydroxybutyrate are acidic, and, if levels of these ketone bodies are too high, the pH of the blood drops, resulting in ketoacidosis.

This happens in untreated Type I diabetes (see diabetic ketoacidosis), and also in alcoholics after binge drinking and subsequent starvation (see alcoholic ketoacidosis).

See also

References

Types of Fats in Food
  • Unsaturated fat
  • Monounsaturated fat
  • Polyunsaturated fat
  • Trans fat
  • Omega: 3, 6, 9

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energy (from the Greek ενεργός, energos, "active, working")[1] is a scalar physical quantity that is a property of objects and systems of objects which is conserved by nature.
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heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.
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In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing,
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Fasting is primarily the act of willingly abstaining from some or all food, drink, or both, for a period of time. Concerning that from which one fasts, and the period of fasting, a fast may be total or partial.
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Acetoacetic acid is the organic compound with the formula CH3C(O)CH2CO2H. It is the simplest beta-keto acid group and like other members of this class is unstable.
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beta-Hydroxybutyric acid (beta-hydroxybutyrate or 3-hydroxybutyric acid) is a ketone body. It is a chiral compound having two enantiomers, D-3-hydroxybutyric acid and L-3-hydroxybutyric acid.
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The chemical compound acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is the simplest representative of the ketones.
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beta-Hydroxybutyric acid (beta-hydroxybutyrate or 3-hydroxybutyric acid) is a ketone body. It is a chiral compound having two enantiomers, D-3-hydroxybutyric acid and L-3-hydroxybutyric acid.
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A ketone (pronounced as key tone) is either the functional group characterized by a carbonyl group (O=C) linked to two other carbon atoms or a chemical compound that contains this functional group.
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liver is an organ present in vertebrates and some other animals. It plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification.
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Acetoacetic acid is the organic compound with the formula CH3C(O)CH2CO2H. It is the simplest beta-keto acid group and like other members of this class is unstable.
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beta-Hydroxybutyric acid (beta-hydroxybutyrate or 3-hydroxybutyric acid) is a ketone body. It is a chiral compound having two enantiomers, D-3-hydroxybutyric acid and L-3-hydroxybutyric acid.
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Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to Krebs Cycle to be oxidized for energy production.
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citric acid cycle, also known as the tricarboxylic acid (TCA) cycle, the Krebs cycle, or Szent-Györgyi-Krebs cycle (after Hans Adolf Krebs and Albert Szent-Györgyi who first determined the chemical intermediates and reaction sequence of the cycle), is a series
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heart is a muscular organ responsible for pumping blood through the blood vessels by repeated, rhythmic contractions, or a similar structure in the annelids, mollusks, and arthropods.
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In animals, the brain or encephalon (Greek for "in the skull"), is the control center of the central nervous system, responsible for behavior. The brain is located in the head, protected by the skull and close to the primary sensory apparatus of vision, hearing,
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Glucose (Glc), a monosaccharide (or simple sugar), is an important carbohydrate in biology. The living cell uses it as a source of energy and metabolic intermediate.
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Blood sugar is a term used to refer to the amount of glucose in the blood. Glucose, transported via the bloodstream, is the primary source of energy for the body's cells.

Blood sugar concentration, or glucose level, is tightly regulated in the human body.
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Lipids can be broadly defined as any fat-soluble (hydrophobic), naturally-occurring molecules. The term is more-specifically used to refer to fatty-acids and their derivatives (including tri-, di-, and monoglycerides and phospholipids) as well as other fat-soluble sterol-containing
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axon or nerve fiber, is a long, slender projection of a nerve cell, or neuron, that conducts electrical impulses away from the neuron's cell body or soma.

Anatomy


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Acetyl-CoA is an important molecule in metabolism, used in many biochemical reactions. Its main use is to convey the carbon atoms within the acetyl group to Krebs Cycle to be oxidized for energy production.
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Ketogenesis is the process by which ketone bodies are produced as a result of fatty acid breakdown.

Production

Ketone bodies are produced mainly in the mitochondria of liver cells.
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liver is an organ present in vertebrates and some other animals. It plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification.
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Fatty acids are an important source of energy for many organisms. Excess glucose can be stored efficiently as fat. Triglycerides yield more than twice as much energy for the same mass as do carbohydrates or proteins.
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The chemical compound acetone (also known as propanone, dimethyl ketone, 2-propanone, propan-2-one and β-ketopropane) is the simplest representative of the ketones.
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Decarboxylation is any chemical reaction in which a carboxyl group (-COOH) is split off from a compound as carbon dioxide (CO2).

In biochemistry

Common biosynthetic decarboxylations of amino acids to amines are:
  • tryptophan to tryptamine

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