CLINICAL CASES
329
Diglyceride: A glycerol molecule with two hydroxyl groups esterified with
a fatty acid moiety.
Monoglyceride: A glycerol molecule with one hydroxyl group esterified
with a fatty acid moiety.
D ISC U SSIO N
Malnutrition and its ultimate form starvation arise from many different causes
and are present even in affluent societies. The case description reveals that the
child lives in a third-world country, and the physical findings reveal that the
child suffers from protein-calorie-deficient starvation, or marasmus.
Fasting and starvation represent changes from the baseline metabolic inter-
actions between tissues that exist in the fed state. Each of three states—fed,
fasting, and starvation—must be considered from the standpoint of the whole
body primarily because the constituent tissues have different requirements for
their nutritional sources. For example, red blood cells have an absolute
requirement for glucose as the exclusive food source from which energy is
derived. Although other tissues use fatty acids and amino acids as well, the red
blood cell cannot because it lacks mitochondria and therefore the enzymes
required for most of the metabolic steps required in P-oxidation of fatty acids
and metabolism of the carbon skeletons of amino acids. Brain tissue normally
has an exclusive preference for glucose, the exception being in advanced
starvation when the brain can use ketone bodies for energy production.
The metabolic interactions of tissues in the fed state are shown in Figure 36-1.
Glucose, fatty acids from triglycerides, and amino acids are provided by the
diet and used differentially by the tissues. In the liver, glucose is used for stor-
age as glycogen or converted to fatty acids for formation into triglycerides
for storage in adipose tissue. Amino acid carbon skeletons are used for meta-
bolic intermediates for energy production or fatty acid synthesis. Resting mus-
cle takes up glucose and stores it as glycogen and uses amino acids for protein
synthesis. Resting muscle prefers fatty acids and ketone bodies over glucose to
satisfy its energy demands. In adipose tissue, glucose and fatty acids are taken
up. Glucose metabolism provides energy and glycerol 3-phosphate for triglyc-
eride formation and storage using fatty acids transported to adipose cells as
triglycerides in lipoprotein particles. The brain and red blood cells take up glu-
cose from blood to meet energy demands.
During circumstances of no food intake for 16 to 20 hours (the postfeeding
state), substantial changes occur in the interactions between tissues, as shown
in Figure 36-2. The liver shifts from consumption of glucose for glycogen stor-
age to mobilization of its glycogen stores to release glucose to the bloodstream
to supply the glucose requirements of the brain and red blood cell. Because the
hepatic glycogen supply is depleted fairly quickly, metabolic signals increase
liver gluconeogenesis, depleting tricarboxylic acid cycle intermediates and
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