During this interval, transient increases in plasma glucose,
amino acids and TAG is seen
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Islet tissue of pancreas responds to elevated level of
glucose with increased secretion of insulin and decreased
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secretion of glucagonThe elevated insulin/glucagon ratio and the ready
availability of circulating substrates make the absorptive
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state an anabolic period characterized by increase
synthesis of TAG and glycogen as well as increased
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synthesis of proteinDuring this absorptive period, virtually all tissues use
glucose as a fuel, and metabolic response of the body
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is dominated by alterations in the metabolism of liver,adipose tissue, skeletal muscle and brain
LIVER:NUTRITION DISTRIBUTION
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CENTERThe liver is uniquely situated to process and distribute
dietary nutrients because the venous drainage of the
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gut and pancreas passes through the hepatic portal
vein before entry in to general circulation
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Thus, after a meal, the liver is bathed in bloodcontaining absorbed nutrients and elevated levels of
insulin secreted by pancreas
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During the absorptive phase, the liver takes up
carbohydrates, lipids and most amino acids
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ADIPOSE TISSUE: ENERGY STORAGEDEPOT
Adipose is second only to liver in its ability to
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distribute fuel molecule
In a 70 kg man, white adipose tissue weighs around 14
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kg or about half as much as total muscle massNearly the entire volume of each adipocyte in WAT
can be occupied by anhydrous,calorically dense TAG
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SKELETAL MUSCLE
Skeletal muscle accounts for nearly 40% of the body
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mass in individuals of healthy weight and it can useglucose, amino acids, and ketone bodies as fuel.
Skeletal muscle is unique in being able to respond to
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substantial changes in the demand for ATP that
accompanies muscle contraction
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At rest, muscle accounts for 25% of oxygenconsumption of the body ,whereas during vigorous
exercise ,it is responsible for up to 90% of total
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oxygen consumed
BRAIN
Although contributing only 2% of adult
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weight, brain accounts for a consistent 20%
of basal oxygen consumption of the body
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at restIn the fed state, brain exclusively uses
glucose as a fuel ,completely oxidising
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140g/day to carbon dioxide and water
OVERVIEW OF FASTING STAGE
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Fasting begins if no food is ingested after the absorptive
period
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It may result from inability to obtain food, the desire tolose weight or clinical situation in which an individual can
not eat
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In the absence of food, plasma level of glucose falls,
triggering a decline in insulin secretion and increase in
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glucagon, epinephrine and cortisol secretionDecrease insulin/glucagon ratio and decreased availability
of circulating substrates make the postabsorptive period a
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catabolic period characterized by degradation of glycogen,
TAG and protein
Starve cycle is divided in two four stages:
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Early fasting (4-16 hrs after food)Prolonged Fasting (16-48 hrs after food)
Starvation (2-3 days without food)
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Prolonged starvation (>5 days without food)
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