physiology notes: endocrine system

PHYSIOLOGY: ENDOCRINE SYSTEM

NOTES

1. Endocrine Glands: secrete hormones directly into the bloodstream, affecting a specific target tissue.

2. Amines: hormones derived from amino acids tyrosine and tryptophan; these are secreted by adrenal medulla, thyroid, and pineal glands.

Polypeptides: amino acid chains less than 100 amino acids in length; Example:insulin

Glycoproteins: polypeptides over 100 amino acids attached to one or more

Carbohydrate groups. Example: FSH, LH

Steroids: lipid hormones formed from cholesterol. Example: testosterone,

estrogens.

3. Hormone precursors: inactive forms of hormones that must be altered to be effective.

    

4. Examples of precursors:

   1. Prohormone: precursors of polypeptide hormones that must be spliced or cut to generate a working hormone. Example: insulin derived from proinsulin.

    

4. 2. prehormone: endocrine gland secretion may be inactive and must be modified by the target cell to generate its effect. Example: thyroid hormone is modified in target cells→ functional form.

5. Lipophilic hormones: can cross cell membrane of target cell and bind to a receptor in cytoplasm or nucleus; hormone and receptor bind to various genes activating them directly

6. Polar hormones: unable to enter the cell; must under signal transduction.

7. Signal transduction:

   1. Cell membrane of target cell with receptors

   2. Second messenger is generated→hormone effect

8. Second messengers: 3 types:

   1. Cyclic AMP: binding to receptor activates G-protein

-G protein activates adenylate cyclase

-adenylate cyclase makes cAMP out of ATP

-cAMP activates protein kinase

-protein kinase activates various enzymes by adding phosphate (PO )

-active enzymes change metabolism of the cell

9. Role of Calcium: binding of a hormone activates a G-protein which in turn

Causes endoplasmic reticulum to release Ca+ into cytoplasm;

-Ca+ activates protein kinase

-protein kinase activates various enzymes by adding PO to them.

10. Tyrosine kinase:

-binding of the hormone activates tyrosine kinase

-tyrosine kinase adds phosphate to the tyrosine of various enzyme→activation

-active enzymes change metabolism of the cell

11. Anterior pituitary lobe hormones:

    1. adrenocorticotropic hormone: stimulates adrenal cortex to secret glucocorticoids.

11. 2. Thyroid stimulating hormone: stimulates thyroid gland→thyroxine

    3. Follicle stimulating hormone: stimulates growth of ovarian follicles;

sperm production

d .Leuteinizing hormone: stimulates ovulation: testes→testosterone

11. 4. Growth hormone: promotes overall tissue and organ growth

    5. Prolactin: stimulates lactation

12. Posterior Pituitary: hormones made in hypothalamus:

    1. Antidiuretic hormone: promotes water retention in kidneys

    2. Oxytocin: causes uterine contraction during child birth

13. Adrenal Cortex hormones:

    1. Aldosterone: regulates Na+ and K+ balance in body

    2. Glucocorticoids: regulates metabolism of glucose

    3. Sex steroids: weak androgens supplement gonads

14. Adrenal Medulla: releases epinephrine as part of sympathetic system

15. Thyroid gland: releases tetraiodothyronine, changed to triiodothyronine at

receptor site; determines basal metabolic rate

16. Pancreatic hormones stimulated by blood levels of glucose

17. Insulin: blood glucose↑; promotes movement of glucose into cells;

storage of glucose as glycogen

Glucagon: blood glucose↓: promotes release of glucose from glycogen and release of stored fat.

18. Pineal Gland: releases melatonin in response to light; sets body’s circadian rhythms in synch with light/dark cycles.

19. Thymus: involved with maturation of T –cell lymphocytes

20. Gonadal hormones:

    1. Testes→testosterone; secondary sex traits; fertility

    2. Ovaries→estrogen and progesterone: secondary sex traits; menstrual cycle