How Are Ketones Excreted From The Body

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Utilization Of Ketone Bodies, Regulation And Clinical Significance Of Ketogenesis

Ketone bodies are utilized by extra hepatic tissues via a series of cytosolic reactions that are essentially a reversal of ketone body synthesis; the ketones must be reconverted to acetyl Co A in the mitochondria (figure-1) Steps 1) Utilization of β-Hydroxy Butyrate Beta-hydroxybutyrate is first oxidized to acetoacetate with the production of one NADH (Figure-1, step-1). In tissues actively utilizing ketones for energy production, NAD+/NADH ratio is always higher so as to drive the β-hydroxybutyrate dehydrogenase catalyzed reaction in the direction of acetoacetate synthesis. Biological significance D (-)-3-Hydroxybutyrate is oxidized to produce acetoacetate as well as NADH for use in oxidative phosphorylation. D (-)-3-Hydroxybutyrate is the main ketone body excreted in urine. 2) Utilization of Acetoacetate a) Coenzyme A must be added to the acetoacetate. The thioester bond is a high energy bond, so ATP equivalents must be used. In this case the energy comes from a trans esterification of the CoASH from succinyl CoA to acetoacetate by Coenzyme A transferase (Figure-1, step-2), also called Succinyl co A: Acetoacetate co A transferase, also known as Thiophorase. The Succinyl CoA com Continue reading >>

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  1. HopefulMDclass2020

    Which of the following are likely fates of acetone in the body?
    I. Excretion in the urine
    II. Conversion back to acetoacetate
    III. Involvement in the anabolism of amino acids
    I only (Correct answer)
    I and II only
    II and III only
    I, II, and III
    "A is correct. This question is asking us to determine from the passage the likely fate of acetone. The passage mentions that acetone has no metabolic utility. Thus choices II and III are incorrect. Acetone is simply excreted in the urine.
    B, C, D: All of these choices include either II or III, which incorrectly describle metabolic uses for acetone in the body."
    I was under the impression that ketone bodies enter circulation and can be taken up by other cells and converted back to acetyl-CoA. I will admit that the passage implied that acetone had no metabolic use, and I should have answered the question off the passage information and not my background information. But I was wondering what y'all think.

  2. HopefulMDclass2020

    This might be useful also. Showing the one way conversion of acetone. I am just a little confused because I thought ketone bodies HAD metabolic use

  3. HopefulMDclass2020

    Welp, I just did some googling and found the answer. The only two ketone bodies are beta-hydroxybutyrate and acetoacetate, while acetone is just a waste product. "The product of the decarboxylation reaction, acetone, is a volatile waste product, and is largely excreted via the lungs."
    Hopefully this can help someone in the future with a similar problem.

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