Page 134 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

90 SECTION II BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM BIOCHEmISTRY ``BIOCHEMISTRY—METABOlISM

Ketone bodies In the liver, fatty acids and amino acids Ketone bodies: acetone, acetoacetate,
are metabolized to acetoacetate and β-hydroxybutyrate.
β-hydroxybutyrate (to be used in muscle Breath smells like acetone (fruity odor).
and brain). Urine test for ketones can detect acetoacetate,
In prolonged starvation and diabetic but not β-hydroxybutyrate.
ketoacidosis, oxaloacetate is depleted for RBCs cannot utilize ketones; they strictly use
gluconeogenesis. In alcoholism, excess NADH glucose.
shunts oxaloacetate to malate. All of these HMG-CoA lyase for ketone production.
processes lead to a buildup of acetyl-CoA, HMG-CoA reductase for cholesterol synthesis.
which is shunted into ketone body synthesis.

Hepatocyte Blood Extrahepatic tissues
(liver) (eg, skeletal muscle)
2 Acetyl-CoA
Expired by lungs
Fatty acids, amino acids Acetoacetyl-CoA

Acetyl-CoA
TCA cycle
Acetone
HMG-CoA

Acetoacetate Acetoacetate Acetoacetate

β-hydroxybutyrate β-hydroxybutyrate β-hydroxybutyrate
ATP

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