CHAPTER 31ORGANIZATION AND CONTROL OF THE ENDOCRINE SYSTEM

Essentials of Pathophysiology

PRE LECTURE QUIZ TRUE/FALSE The endocrine system uses chemical

substances called hormones as a means of regulating and integrating body functions.

All hormones can cross the cell membrane. The hypothalamus controls the release of

pituitary hormones. The pituitary gland has been called the

master gland because its hormones control the function of many target glands and cells.

Glucagon, insulin, and epinephrine receptors are examples of surface (second messenger) receptors.

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PRE LECTURE QUIZ Hormones exert their action by binding to high-

affinity _________________ located either on the surface or inside the target cells.

Decreased hormone levels often produce an increase in receptor numbers by means of a process called _________________ ; this increases the sensitivity of the body to existing hormone levels.

The ________________ and pituitary form a unit that exerts control over many functions of several endocrine glands as well as a wide range of other physiologic functions.

Negative _________________ mechanisms regulate the level of many of the hormones in the body.

 Hormone secretions acting locally on cells other than those that produced the hormone is known as a ___________________ action.

Feedback

Hypothalamus

paracrine

Receptors

up-regulation

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

HORMONES (CONT.)

• Hormones can affect cells nearby or far away

• Endocrine – distant• Paracrine – Nearby• Autocrine – Self stimulating

QUESTION

Your patient has low levels of circulating thyroid stimulating hormone. How will the cells of the thyroid gland respond?

a. No responseb. Response will depend upon the levels

of TSH.c. Down-regulationd. Up-regulation

ANSWER

d. Up-regulationRationale: 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 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

Tell whether the following statement is true or false.

Steroid hormones are all derived from cholesterol.

ANSWER

TrueRationale: The adrenal sex hormones,

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

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?

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

SCENARIO

A man with liver failure has developed:

Hypokalemia Hypotension Hyperglycemia Repeated infectionsQuestion: What hormone imbalances do

you suspect? Why?

HYPOTHALAMUSThe hypothalamus knows the state

of the body: Temperature Blood osmolarity Blood nutrients Blood hormone levels Inflammatory mediators in blood Emotions Pain

THE HYPOTHALAMUS MAKES RELEASING HORMONES

Releasing hormones are sent to the pituitary via the hypophyseal portal system

Hypothalamus

Anterior pituitary

Hypophyseal portal system

(Image reproduced from Bowne, P.S. [2004]. CRH release tutorial. Used with author’s permission.)

THE PITUITARY (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

Tell whether the following statement is true or false.

The pituitary gland controls the release of thyroid hormone.

ANSWER

TrueRationale: The pituitary gland (on a cue

from the hypothalamus) tells other organs or glands to produce and secrete or inhibit the appropriate hormones.

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?