Regulation of Organic Metabolism and Energy Balance
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
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
8. List the overall responses of muscle, adipose tissue, and liver to
insulin. What effects occur when plasma insulin concentration
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
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
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
22. What is the signiﬁ cance of the ratio of LDL cholesterol to
islets of Langerhans
SECTION A CLINICAL TERMS
type 1 diabetes mellitus
type 2 diabetes mellitus
Regulation of Total-Body Energy
Balance and Temperature
Basic Concepts of
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 (
) during break-
down of an organic molecule can either appear as heat (
be used to perform work (