Ketone bodies

Ketone bodies are water-soluble molecules produced by the liver from fatty acids during periods of low food intake (fasting), carbohydrate restrictive diets, starvation, prolonged intense exercise, or in untreated (or inadequately treated) type 1 diabetes mellitus. They consist of acetoacetate, β-hydroxybutyrate, and their spontaneous breakdown product, acetone.

Biosynthesis of Ketone Bodies

The process of ketone bodies formation, known as ketogenesis, occurs in the mitochondrial matrix of liver cells. When glucose levels are low, ketogenesis is triggered to generate alternative energy substrates. This involves the conversion of acetyl-CoA derived from β-oxidation of fatty acids into acetoacetate, which is later converted into β-hydroxybutyrate or acetone.

Role in Energy Metabolism

Ketone bodies play a crucial role in energy metabolism. During periods of carbohydrate restriction, they provide an energy source for peripheral tissues, especially the brain, heart, and skeletal muscle. The brain, notably, cannot utilize fatty acids as a fuel source and hence relies on ketone bodies as an alternative to glucose.

Ketosis and Ketonuria

Ketosis refers to the state where the concentration of ketone bodies in the blood is higher than normal. This usually occurs when the body is mobilizing stored fat as an energy source rather than carbohydrates. When the concentration of ketone bodies exceeds the body's capacity to reabsorb them, they begin to appear in urine, a condition referred to as ketonuria.

Clinical Significance

In the clinical context, excessive production of ketone bodies leads to a condition known as ketoacidosis, which is commonly seen in untreated type 1 diabetes mellitus. Symptoms may include fruity-scented breath, dry mouth, shortness of breath, confusion, and in severe cases, it can lead to coma or death.

See Also

• Ketosis
• Ketoacidosis
• Fatty acid metabolism
• Carbohydrate metabolism

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