358
Chapter 11
Chapter 11 Quantitative and Thought Questions
6. A drug that blocks the action of norepinephrine is injected
directly into the hypothalamus of an experimental animal, and
the secretion rates of several anterior pituitary hormones are
observed to change. How is this possible, given the fact that
norepinephrine is not a hypophysiotropic hormone?
7. A person is receiving very large doses of a cortisol-like drug to
treat her arthritis. What happens to her secretion of cortisol?
8. A person with symptoms of hypothyroidism (for example,
sluggishness and intolerance to cold) is found to have
abnormally low plasma concentrations of T
4
, T
3
, and TSH.
After an injection of TRH, the plasma concentrations of all
three hormones increase. Where is the site of the defect leading
to the hypothyroidism?
9. A full-term newborn infant is abnormally small. Is this most
likely due to defi cient growth hormone, defi cient thyroid
hormones, or defi cient nutrition during fetal life?
10. Why might the administration of androgens to stimulate
growth in a small 12-year-old male turn out to be
counterproductive?
(Answers appear in Appendix A.)
1. In an experimental animal, the sympathetic preganglionic fi bers
to the adrenal medulla are cut. What happens to the plasma
concentration of epinephrine at rest and during stress?
2. During pregnancy there is an increase in the liver’s production
and, consequently, the plasma concentration of the major
plasma binding protein for the thyroid hormones (TH). This
causes a sequence of events involving feedback that results in an
increase in the plasma concentration of TH, but no evidence of
hyperthyroidism. Describe the sequence of events.
3. A child shows the following symptoms: defi cient growth; failure
to show sexual development; decreased ability to respond to
stress. What is the most likely cause of all these symptoms?
4. If all the neural connections between the hypothalamus
and pituitary were severed, the secretion of which pituitary
hormones would be affected? Which pituitary hormones would
not be affected?
5. Typically, an antibody to a peptide combines with the peptide
and renders it nonfunctional. If an animal were given an
antibody to somatostatin, the secretion of which anterior
pituitary hormone would change and in what direction?
Chapter 11 Answers to Physiological Inquiries
Figure 11–3
By storing large amounts of hormone in an
endocrine cell, the plasma level of the hormone can be
increased within seconds when the cell is stimulated. Such
rapid responses may be critical for an appropriate response to a
challenge to homeostasis. Packaging peptides in this way also
prevents intracellular degradation.
Figure 11–13
Because the amount of blood into which the
hypophysiotropic hormones are secreted is far less than would
be the case if they were secreted into the general circulation of
the body, the absolute amount of hormone required to achieve
a given concentration is much less. This means that the cells
of the hypothalamus need only synthesize a tiny amount of
hypophysiotropic hormone to reach concentrations in the portal
blood vessels that are physiologically active (i.e., can activate
receptors on pituitary cells). This allows for the tight control of
the anterior pituitary gland by a very small number of discrete
neurons within the hypothalamus.
Figure 11–19
Plasma cortisol levels would increase. This would
result in decreased ACTH levels in the systemic blood, and
CRH levels in the portal vein blood, due to increased negative
feedback at the pituitary and hypothalamus, respectively.
The right adrenal gland would shrink in size (atrophy) as a
consequence of the reduced ACTH levels (decreased “trophic”
stimulation of the adrenal cortex).
Figure 11–29
His elevated height compared to the height of his
identical twin indicates that growth hormone had been elevated
in his blood prior to puberty, resulting in gigantism. Once
growth ceased, his features enlarged due to continued excess
GH, resulting in acromegaly. This patient is referred to as an
“acromegaloid giant.”
Figure 11–33
The 1-hydroxylase activity will stimulate the
conversion of 25-OH D to 1,25-(OH)
2
D in the granulomas
themselves; the 1,25-(OH)
2
D will then diffuse out of the
granuloma cells and enter the plasma, leading to increased
calcium absorption in the gastrointestinal tract. This will increase
plasma calcium, which in turn will suppress parathyroid hormone
production and, consequently, plasma parathyroid hormone levels
will decrease. This is a form of secondary hypoparathyroidism.
12. Which of the following is
not
consistent with primary
hyperparathyroidism?
a. hypercalcemia
b. elevated plasma 1,25-(OH)
2
D
c. phosphaturia
d. a decrease in calcium resorption from bone
e. an increase in calcium reabsorption in the kidney
True/False
13. T
4
is the chief circulating form of thyroid hormone, but is less
active than T
3
.
14. Acromegaly is usually associated with hypoglycemia and
hypotension.
15. Thyroid hormones and cortisol are both permissive for
epinephrine’s actions.
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