1. Chapter 30 Organization and Control of the Endocrine System

2. 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

3. Hormones (cont.)
Hormones can affect cells nearby or far away

4. Question
Your patient has low levels of circulating thyroid hormone. How will the cells of the thyroid gland respond?
No response
Response will depend upon the levels of TSH.
Down-regulation
Up-regulation

5. Answer
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.

6. 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

7. Question Tell whether the following statement is true or false.
Steroid hormones are all derived from cholesterol.

8. 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.

9. 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?

10. 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

11. Scenario A man with liver failure has developed: Hypokalemia
Hypotension
Hyperglycemia
Repeated infections
Question:
What hormone imbalances do you suspect? Why?

12. Hypothalamus The hypothalamus knows the state of the body: Temperature
Blood osmolarity
Blood nutrients
Blood hormone levels
Inflammatory mediators in blood
Emotions
Pain

13. The Hypothalamus Makes Releasing Hormones
Releasing hormones are sent to the pituitary via the hypophyseal portal system
Hypothalamus
Hypophyseal portal system
Anterior pituitary
(Image reproduced from Bowne, P.S. [2004]. CRH release tutorial. Used with author’s permission.)

14. The Pituitary (Master Gland) Creates Trophic Hormones
Hypothalamus makes releasing hormones
The Pituitary (Master Gland) Creates Trophic Hormones
Which are sent to the anterior pituitary
The anterior pituitary releases its stored trophic hormones into the systemic circulation
They tell other endocrine organs in the body to grow and secrete their hormones
(Image reproduced from Bowne, P.S. [2004]. CRH release tutorial. Used with author’s permission.)

16. Question Tell whether the following statement is true or false.
The pituitary gland controls the release of thyroid hormone.

17. 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.

18. 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?