Chapter031

Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins

Chapter 31

Mechanisms of Endocrine Control

Chapter 31

Mechanisms of Endocrine Control


HormonesHormones

• 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


Hormones (cont.)Hormones (cont.)

Hormones can affect cells nearby or far away.


Question 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


Answer Answer

d. Up-regulation

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.


Hormones (cont.)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


Question Question

Tell whether the following statement is true or false:

Steroid hormones are all derived from cholesterol.


Answer Answer

True

The adrenal sex hormones, glucocorticoids, and mineralocorticoids all arise from cholesterol and have similar chemical structures even though their functions are slightly different.


ScenarioScenario

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?


After Hormones Affect Body CellsAfter 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


ScenarioScenario

A man with liver failure has developed…

• Hypokalemia

• Hypotension

• Hyperglycemia

• Repeated infections

Question

• What hormone imbalances do you suspect? Why?


HypothalamusHypothalamus

Hypothalamus knows the state of the body:

• Temperature

• Blood osmolarity

• Blood nutrients

• Blood hormone levels

• Inflammatory mediators in blood

• Emotions

• Pain


Pituitary (Master Gland)Creates Trophic HormonesPituitary (Master Gland)

Creates Trophic Hormones

They tell other endocrine organs in the body to grow and secrete their 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.)


Question Question

Tell whether the following statement is true or false:

The pituitary gland controls the release of thyroid hormone.


Answer Answer

True

The pituitary gland (on a cue from the hypothalamus) tells other organs or glands to produce and secrete or inhibit the appropriate hormones.


DiscussionDiscussion

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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