🐭 RAT series
Points to Ponder for NEET-PG, FMGE & NEXT
- Acetone, acetoacetate, and beta-hydroxybutyrate are the three ketone bodies.
- Ketone bodies serve as an alternative energy source for some tissues, but not the liver.
- Ketone bodies are produced in the liver during carbohydrate deprivation.
- Starvation and uncontrolled diabetes are the main stimuli for ketogenesis.
- Skeletal muscle, brain, and cardiac muscle can utilize ketone bodies for energy under certain conditions.
Definition
- Ketone bodies are a group of three water-soluble molecules produced in the liver during periods of limited carbohydrate availability.
- They serve as an alternative energy source for some tissues when glucose is scarce.
Formation (Ketogenesis):
- Occurs in the liver when the rate of fatty acid oxidation is high, leading to excess acetyl-CoA.
- Acetyl-CoA is the primary substrate for ketogenesis.
- Stimuli for ketogenesis:
- Starvation: Depleted glycogen stores and low blood sugar levels.
- Uncontrolled diabetes mellitus: Absolute or relative insulin deficiency.
Types of Ketone Bodies:
- Acetone
- Acetoacetate
- Beta-hydroxybutyrate (most abundant)
Formation (Ketogenesis):
- Occurs in the liver under conditions of high fatty acid oxidation and low oxaloacetate availability.
- Stimulus: Low insulin levels lead to increase in Glucagon secretion, stimulating hormone-sensitive lipase in adipose tissue, which breaks down triglycerides in adipose tissue, releasing free fatty acids.
- Fatty acid oxidation: Free fatty acids are transported to the liver and broken down into acetyl-CoA.
- Limited Citric Acid Cycle Entry:
- Glycerol enters gluconeogenesis for glucose synthesis (in an attempt to maintain blood sugar levels).
- Oxaloacetate (required for TCA cycle entry) is depleted due to its use in gluconeogenesis.
- With limited oxaloacetate available, acetyl-CoA cannot fully enter the citric acid cycle for energy production and accumulates.
- Ketogenesis Pathway: Excess acetyl-CoA is converted into ketone bodies by the liver..
Utilization:
- Ketone bodies are released into the bloodstream and can be utilized by some tissues as an alternative fuel source:
- Skeletal muscle: Can use ketone bodies for energy to varying degrees.
- Brain: In prolonged starvation, the brain can adapt to utilize ketone bodies for a significant portion of its energy needs.
- Cardiac muscle: Particularly in starvation, the heart can utilize ketone bodies as an energy source.
- The liver cannot utilize ketone bodies directly due to the lack of the enzyme succinyl-CoA acetoacetate transferase.
