934
UNIT 4
Maintenance of the Body
24
most of the fat mobilized is converted to ketone bodies. Gluca-
gon release is inhibited aFer the next meal or whenever blood
glucose levels rise and insulin secretion begins again.
So far, the picture is pretty straightforward. Increasing blood
glucose levels trigger insulin release, which “pushes” glucose
out of blood and into cells. Tis drop in blood glucose stimu-
lates secretion of glucagon, which “pulls” glucose from the cells
Glucagon targets the liver and adipose tissue
(Figure 24.21)
.
Hepatocytes respond by accelerating glycogenolysis and gluco-
neogenesis. Adipose cells mobilize their fatty stores (lipolysis)
and release fatty acids and glycerol to the blood. In this way,
glucagon “refurbishes” blood energy sources by enhancing
both
glucose and fatty acid levels. Under certain hormonal condi-
tions and persistent low glucose levels or prolonged fasting,
(b) Principal pathways of the postabsorptive state
(a) Major events of the postabsorptive state
Major energy fuels:
glucose provided by glycogenolysis and
gluconeogenesis; fatty acids, and ketones
Liver metabolism:
amino acids converted to glucose
Major metabolic thrust:
catabolism and replacement of fuels in blood
Amino acids
Amino acids
Fatty acids
Glycerol
Amino
acids
ATP
Proteins
Fatty
acids +
glycerol
Ketone
bodies
Blood glucose
Glucose
Keto
acids
Keto acids
Stored
glycogen
Glycogen
Glycogen
Protein
Pyruvic and
lactic acids
Triglycerides
Triglycerides
Pyruvic and
lactic acids
Glucose
Fatty acids
and ketones
Glucose
Amino acids
Keto acids
Glucose
Triglycerides
Glycerol and
fatty acids
In nervous
tissue:
In liver:
In most tissues:
In adipose
tissue:
In muscle:
CO
2
+ H
2
O
+
ATP
CO
2
+ H
2
O
+
ATP
CO
2
+ H
2
O
+
ATP
CO
2
+ H
2
O
+
ATP
CO
2
+ H
2
O
+
1
2
2
2
3
3
3
4
4
4
Figure 24.20
Major events and principal metabolic pathways of the postabsorptive state.
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