breakdown of triglycerides in adipose tissue and the slower hepatic tricar-
boxylic acid cycle. In spite of the utilization of ketone bodies by peripheral tis-
sues and the brain and central nervous system (CNS) tissues after 5 to 6 weeks
of starvation, ketone body blood levels rise, spill over into the urine and are
excreted in significant quantity wasting material that could be used for energy
generation because the tissues capable of using ketone bodies as fuel are
already using the maximum possible amount. Thus the major differences
between starvation and the postfeeding fast are the adaptive ability of the brain
and central nervous system to use ketone bodies to satisfy some of their energy
demand and in the levels of circulating ketone bodies that are high enough to
spill over into the urine in significant quantities.
C O M P R E H E N SIO N Q U E ST IO N S
An 8-month-old child presents with exhaustion, irritability, and malnutrition.
The family history reveals poverty and inadequate nutrition in all members.
The 8-month-old was fed diluted formula, and the tentative diagnosis of
marasmus was made.
[36.1] In cases of starvation many metabolic changes take place to meet the
body’s metabolic demands. Which of the following illustrates
starvation-triggered changes in intermediary metabolism?
A. Increased dependence of liver on glucose for its energy supply
B. Increased synthesis of proteins in muscle tissue
C. Increased use of ketone bodies for energy source in brain
D. Decreased mobilization of triglycerides by adipose tissue
E. Adaptation of red blood cells to use ketone bodies for energy
Use the reactions below for Question 36.2:
Acetoacetyl-CoA + acetyl-CoA ^ P-hydroxy-P-methylglutaryl-
CoA + CoA
Acetoacetate + NADH ^ P-hydroxybutyrate + NAD+
P-hydroxy-P-methylglutaryl-CoA + H2O ^ acetoacetate +
Acetyl-CoA + acetyl-CoA ^ acetoacetyl-CoA + CoA
Acetoacetate + succinyl-CoA ^ acetoacetyl-CoA + succinate
[36.2] Using the above reactions, which of the following correctly describes
the pathway of ketone body formation?
A. 3 ^ 2 ^ 1 ^ 4
B. 4 ^ 1 ^ 3 ^ 2
C. 4 ^ 2 ^ 3 ^ 1
D. 5 ^ 1 ^ 2 ^ 3
E. 5 ^ 2 ^ 3 ^ 1