Chapter 31 Organization and Control of the Endocrine System Essentials of Pathophysiology Chapter 31 Organization and Control of the Endocrine System

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. T F

Pre lecture quiz Feedback Hypothalamus paracrine Receptors 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 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? No response Response will depend upon the levels of TSH. Down-regulation Up-regulation

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.

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 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.

A man takes dopamine for paralysis caused by his Parkinson disease. 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

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

Hypothalamus The 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 Hypophyseal portal system Anterior pituitary (Image reproduced from Bowne, P.S. [2004]. CRH release tutorial. Used with author’s permission.)

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 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.)

Author: Please add title.

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

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.

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?