Chapter 30
Organization and Control of the
Endocrine System
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Hormones
• Hormones make cells react by attaching to receptors
on their membranes
• A cell will only respond if it has receptors for the
hormone
– Up-regulation: the cell makes more hormone
receptors
– Down-regulation: the cell makes fewer hormone
receptors
• Different cells respond differently to the same
hormone
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Hormones (cont.)
• Hormones
can affect
cells nearby
or far away
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Question
Your patient has low levels of circulating thyroid hormone.
How will the cells of the thyroid gland respond?
a. No response
b. Response will depend upon the levels of TSH.
c. Down-regulation
d. Up-regulation
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Answer
d. Up-regulation
Rationale: When there is diminished hormonal activity,
cells have the ability to make more hormone receptors
and increase the sensitivity of the existing receptors to
the hormone. This is called up-regulation.
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Hormones (cont.)
Hormones can be made of:
• Amino acids
– Epinephrine, dopamine, T3, and T4
• Proteins (peptide hormones)
– Insulin, glucagon, trophic hormones
• Cholesterol (steroid hormones)
– Cortisol, aldosterone, testosterone
• Fatty acids
– Ecosanoids
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Question
Tell whether the following statement is true or false.
Steroid hormones are all derived from cholesterol.
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Answer
True
Rationale: The adrenal sex hormones, glucocorticoids,
and mineralocorticoids all arise from cholesterol and have
similar chemical structures even though their functions
are slightly different.
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Scenario
A man takes dopamine for paralysis caused by his
Parkinson disease.
• At first, a small dose of dopamine was all he needed
• His symptoms improved significantly right after taking it,
but then he froze up again
• Now he needs a high dose, and the effects last only a
little while
Question:
• What has happened to his cells and their receptors?
• The doctor has decided to try giving him an MAO inhibitor
along with his dopamine. Why?
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After Hormones Affect Body Cells
• They may be destroyed by enzymes at the
receptor site
– Epinephrine, dopamine
• They may be taken up by cells and destroyed
– Peptide hormones
• They may be destroyed in the liver and passed
out in the bile
– Steroid hormones
– T3 and T4
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Scenario
A man with liver failure has developed:
• Hypokalemia
• Hypotension
• Hyperglycemia
• Repeated infections
Question:
• What hormone imbalances do you suspect? Why?
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Hypothalamus
The hypothalamus knows the state of the body:
• Temperature
• Blood osmolarity
• Blood nutrients
• Blood hormone levels
• Inflammatory mediators in blood
• Emotions
• Pain
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The Hypothalamus Makes Releasing
Hormones
• Releasing
hormones
are sent to
the pituitary
via the
hypophyseal
portal
system
Anterior
pituitary
Hypothalamus
Hypophyseal
portal
system
(Image reproduced from Bowne, P.S.
[2004]. CRH release tutorial. Used
with author’s permission.)
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
The Pituitary (Master
Gland)
Creates Trophic Hormones
Hypothalamus
makes releasing
hormones
Which are sent to the anterior
pituitary
The anterior pituitary releases its
stored trophic hormones into the
systemic circulation
(Image reproduced from Bowne, P.S. [2004]. CRH
release tutorial. Used with author’s permission.)
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
They tell other
endocrine
organs in the
body to grow
and secrete
their hormones
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Question
Tell whether the following statement is true or false.
The pituitary gland controls the release of thyroid hormone.
Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins
Answer
True
Rationale: The pituitary gland (on a cue from the
hypothalamus) tells other organs or glands to produce
and secrete or inhibit the appropriate hormones.
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Discussion
A man’s hypothalamus has no hormone receptors.
• What will happen to his production of:
– CRH
T3 and T4
– ACTH
FSH
– Cortisol
LH
– Testosterone
GnRH
– TRH
TSH
Question:
• What signs and symptoms do you expect him to have?
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