Regulation of Organic Metabolism and Energy Balance
583
III. Hypoglycemia is defi ned as abnormally low glucose levels in
the blood. It may arise in the fed or fasting state. Symptoms
of hypoglycemia are similar to those of sympathetic nervous
system activation. However, severe hypoglycemia can lead to
brain dysfunction and even death if untreated.
IV. Plasma cholesterol is a precursor for the synthesis of plasma
membranes, bile salts, and steroid hormones.
V. Cholesterol synthesis by the liver is controlled so as to
homeostatically regulate plasma cholesterol concentration; it
varies inversely with ingested cholesterol.
VI. The liver also secretes cholesterol into the bile and converts it
to bile salts.
VII. Plasma cholesterol is carried mainly by low-density
lipoproteins, which deliver it to cells; high-density
lipoproteins carry cholesterol from cells to the liver and
steroid-producing cells. The LDL/HDL ratio correlates with
the incidence of coronary heart disease.
SECTION A KEY TERMS
SECTION A REVIEW QUESTIONS
1. Using a diagram, summarize the events of the absorptive period.
2. In what two organs does major glycogen storage occur?
3. How do the liver and adipose tissue metabolize glucose during
the absorptive period?
4. How does adipose tissue metabolize absorbed triglyceride, and
what are the three major sources of the fatty acids in adipose
tissue triglyceride?
5. What happens to most of the absorbed amino acids when a
high-protein meal is ingested?
6. Using a diagram, summarize the events of the postabsorptive
period; include the four sources of blood glucose and the
pathways leading to ketone formation.
7. Distinguish between the roles of glycerol and free fatty acids
during fasting.
8. List the overall responses of muscle, adipose tissue, and liver to
insulin. What effects occur when plasma insulin concentration
decreases?
9. Describe fi ve inputs controlling insulin secretion and the
physiological signifi cance of each.
10. List the effects of glucagon on the liver and their
consequences.
11. Discuss two inputs controlling glucagon secretion and the
physiological signifi cance of each.
12. List the metabolic effects of epinephrine and the sympathetic nerves
to the liver and adipose tissue, and state the net results of each.
13. Describe the permissive effects of cortisol and the effects that
occur when plasma cortisol concentration increases.
14. List the effects of growth hormone on carbohydrate and lipid
metabolism.
15. Which hormones stimulate gluconeogenesis? Glycogenolysis in
the liver? Glycogenolysis in skeletal muscle? Lipolysis? Blockade
of glucose uptake?
16. Describe how plasma glucose, insulin, glucagon, and
epinephrine levels change during exercise and stress. What
causes the changes in the concentrations of the hormones?
17. Describe the metabolic disorders of severe T1DM.
18. How does obesity contribute to T2DM?
19. Hypersecretion of which hormones can induce a diabetic state?
20. Using a diagram, describe the sources of cholesterol gain
and loss. Include three roles the liver plays in cholesterol
metabolism, and describe the controls over these processes.
21. What are the effects of saturated and unsaturated fatty acids on
plasma cholesterol?
22. What is the signifi cance of the ratio of LDL cholesterol to
HDL cholesterol?
absorptive state
567
alpha cell
572
α
-ketoacid
569
beta cell
572
cholesterol
580
delta cell
572
glucagon
575
gluconeogenesis
570
glucose-counterregulatory
control
574
glucose sparing
570
glycogenolysis
570
glycogen phosphorylase
573
glycogen synthase
573
high-density lipoprotein
(HDL)
581
hormone-sensitive lipase
(HSL)
575
hypoglycemia
574
insulin
572
islets of Langerhans
571
ketone
570
lipolysis
570
lipoprotein
568
lipoprotein lipase
569
low-density lipoprotein
(LDL)
581
postabsorptive state
567
very-low-density lipoprotein
(VLDL)
568
SECTION A CLINICAL TERMS
atherosclerosis
580
diabetes mellitus
578
diabetic ketoacidosis
579
exercise-induced
amenorrhea
578
familial hypercholesterolemia
582
fasting hypoglycemia
580
insulin resistance
578
sulfonylureas
580
type 1 diabetes mellitus
(T1DM)
578
type 2 diabetes mellitus
(T2DM)
578
SECTION B
Regulation of Total-Body Energy
Balance and Temperature
Basic Concepts of
Energy Expenditure
The breakdown of organic molecules liberates the energy
locked in their molecular bonds. Cells use this energy to per-
form the various forms of biological work, such as muscle con-
traction, active transport, and molecular synthesis. The fi rst
law of thermodynamics states that energy can be neither cre-
ated nor destroyed, but can be converted from one form to
another. Thus, internal energy liberated (
E
) during break-
down of an organic molecule can either appear as heat (
H
) or
be used to perform work (
W
).
E
=
H
+
W
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