Endocrine Glands 357- Distinguish between endocrine and autocrine/paracrine
regulation. List some of these autocrine/paracrine regulators
and describe their functions.
Test Your Analytical Ability- Brenda, your roommate, has been having an awful time
lately. She can’t even muster enough energy to go out on a
date. She’s been putting on weight, she’s always cold, and
every time she pops in the workout video she complains of
weakness. When she finally goes to the doctor, he finds her
to have a slow pulse and a low blood pressure. Laboratory
tests reveal that her T 4 is low and her TSH is high. What
is the matter with Brenda? Why are her symptoms typical
of this disorder, and what type of treatment will the doctor
most likely prescribe? - Your friend Bud has the talent to be a star basketball
center—if only he weren’t 5 foot 8. Being well-intentioned
but ignorant, you start injecting him with growth hormone as
he sleeps each night. You think this is a clever strategy, but
after a time you notice that he hasn’t grown an inch. Instead,
his jaw and forehead seem to have gotten disproportionately
large and his hands and feet are swollen. Explain why the
growth hormone didn’t make Bud grow taller and why it had
the effect it did. What disease state do these changes mimic? - You see your friend Joe for the first time in over a year.
When you last saw him, he had been trying to bulk up by
working out daily at the gym, but he was getting discouraged
because his progress seemed so slow. Now, however,
he’s very muscular. In a frank discussion, he admits that
he’s been getting into trouble because he’s become very
aggressive. He also tells you, in strict confidence, that his
testes have gotten smaller and that he’s been developing
breasts! What might Joe be doing to cause these changes?
Explain how these changes came about. - Distinguish between the steroid and nonsteroid group of
nuclear hormone receptors. Explain the central role of
vitamin A in the actions of the nonsteroid group of receptors. - Suppose, in an experiment, that you incubate isolated rat
testes with hCG. What would be the effect, if any, of the
hCG on the testes? Explain your answer. If there was an
effect, discuss its potential significance in research and
clinical settings. - Distinguish between the genomic and nongenomic actions
of steroid hormones. Which mechanism of action would be
inhibited by a drug that interfered with protein synthesis?
Explain. - People who have suffered severe stress may have
difficulties remembering the stressful event. Parts of the
brain, including the hippocampus, are rich in cortisol
receptor proteins. Explain the relationship between these
observations. - Diabetics who require insulin injections can experience what
is called the “dawn phenomenon”—when they first wake up
in the morning, they may require higher doses of insulin to
control their blood glucose. People usually awaken naturally
from REM sleep, which is a sleep stage that is stressful.
Explain the endocrine events that are responsible for the
dawn phenomenon. - Which of these hormones may have a primary role in many
circadian rhythms?
a. Estradiol
b. Insulin
c. Adrenocorticotropic hormone
d. Melatonin - Human chorionic gonadotropin (hCG) is secreted by
a. the anterior pituitary.
b. the posterior pituitary.
c. the placenta.
d. the thymus.
e. the pineal gland.- What do insulin-like growth factors, neurotrophins, nitric
oxide, and lymphokines have in common?
a. They are hormones.
b. They are autocrine or paracrine regulators.
c. They are neurotransmitters.
d. They all use cAMP as a second messenger.
e. They all use Ca^2 1 as a second messenger.
Test Your Understanding
- Explain how regulation of the neurohypophysis and of the
adrenal medulla are related to the embryonic origins of these
organs. - Explain the mechanism of action of steroid hormones and
thyroxine. - Explain why polar hormones cannot regulate their target
cells without using second messengers. Also explain in a
step-by-step manner how cyclic AMP is used as a second
messenger in hormone action. - Describe the sequence of events by which a hormone can
cause an increase in the Ca^2 1 concentration within a target
cell. How can this increased Ca^2 1 affect the metabolism of
the target cell? - Explain the significance of the term trophic with respect to
the actions of anterior pituitary hormones. - Suppose a drug blocks the conversion of T 4 to T 3. Explain
what the effects of this drug would be on (a) TSH secretion,
(b) thyroxine secretion, and (c) the size of the thyroid gland. - Explain why the anterior pituitary is sometimes referred
to as the “master gland,” and provide two reasons why this
description is misleading. - Describe the role of the pituitary-adrenal axis in the response
to stress. What effects on the body does this produce? - Describe how thyroid hormone secretion is regulated.
Explain how this system is affected by (a) iodine deficiency
and (b) ingestion of thyroid hormone pills. - Suppose a person’s immune system made antibodies against
insulin receptor proteins. What effect might this condition
have on carbohydrate and fat metabolism? - Explain how light affects the function of the pineal gland.
What is the relationship between pineal gland function and
circadian rhythms?