revised endocrine.ppt

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revised endocrine.ppt

  1. 1. The Endocrine System Hormones are secreted into the blood by endocrine glands See table 1- some endocrine organs are specialized for hormone secretion Some (e.g., skin, stomach, liver,etc.) have additional functions
  2. 2. (specialized)
  3. 3. What is a hormone? Small molecule that affects metabolism of target organ Amines- from tyrosine and tryptophan adrenal medulla, thyroid, pineal glands Polypeptides and proteins more than 100 amino acids example: growth hormone
  4. 4. Glycoproteins large chain of amino acids with carbohydrates attached (FSH and LH) Steroids derived from cholesterol progesterone, cortisol, testosterone (only by adrenal gland and gonads) Some are synthesized as a precursor and later activated Some are polar, some lipid-soluble- these can pass through cell membranes if small enough
  5. 5. Endocrine vs neural control A lot of overlap some polypeptides are hormones AND neurotransmitters Neurotransmitters do not travel in the blood, but across a synaptic cleft Neural control generally considered faster- acting
  6. 6. Common requirements target cells must have specific receptors for the hormone/neurotransmitter binding to receptor must trigger specific changes in the target cell mechanism for quickly switching off the activity (removal or inactivation of the hormone/neurotransmitter)
  7. 7. Effects of hormones One tissue can respond to many hormones Synergistic effect - hormones work together to produce a result Example: epinephrine and norepinephrine have an additive effect to increase heart rate FSH and testosterone have complementary effect on sperm production
  8. 8. Permissive effect - one hormone enhances the effect of another Glucocorticoids enhance effectiveness of catecholamines (epinephrine and norepinephrine) Antagonist effect - one hormone opposes the effect of another insulin promotes fat formation glucagon promotes fat breakdown
  9. 9. Modulation of hormone effect Hormones do not usually accumulate in blood half-life usually several hours; usually deactivated in liver Concentration is important Physiological range- normal activity Pharmacological (high) range may affect other cells may affect other hormone levels
  10. 10. Priming hormone binds  more receptors synthesized  more hormone can bind cell Downregulation- prolonged exposure to high hormone levels can reduce receptor expression. Cells are therefore desensitized Some hormones are therefore secreted in spurts
  11. 11. Mechanisms of hormone action Lipophilic (steroids and thyroxine) pass through membrane bind receptors inside target cells in cytoplasm or nucleus
  12. 13. Water-soluble hormones can’t pass through membrane bond to receptors on cell (membrane) surface “ Second messenger” activation required adenylate cyclase-cAMP phospholipase C- calcium
  13. 15. Some important endocrine glands Pituitary gland anterior lobe secretes its own hormones regulated by hypothalamus feedback control posterior lobe- neural tissue stores and releases products of hypothalamus
  14. 19. Adrenal glands- paired organs that sit “on top” of the kidneys Outer cortex and inner medulla have different functions Medulla- catecholamines (epinephrine, norepinephrine) stimulated by sympathetic nerves Cortex- controlled by ACTH from anterior pituitary
  15. 20. Cortex secretes steroid hormones (corticosteroids) Mineralocorticoids- regulate Na and K balance aldosterone Glucocorticoids- regulate glucose metabolism cortisol Androgens, supplement sex steroids secreted by gonads
  16. 22. Adrenal medulla- innervated by sympathetic nervous system “ Fight or flight” rise in blood glucose rise in blood fatty acids Sustained stress- general adaptation syndrome 1. Alarm 2. Resistance 3. Exhaustion
  17. 23. Thyroid and parathyroid glands Thyroglobulin+ iodine = thyroxine (T4) and triiodothyronine (T3) Released from precursor (thyroxine) through action of TSH Protein synthesis Maturation of nervous system Increase rate of cell respiration
  18. 24. Calcitonin released by parafollicular cells works with parathyroid hormone inhibits dissolution of bone stimulates excretion of calcium in urine (lowers blood calcium levels)
  19. 25. Thyroid diseases Iodine deficiency goiter can’t make enough T3 and T4 no inhibition of TSH stimulates abnormal thyroid growth Hypothyroid low metabolic rate; inability to adapt to cold myxedema (swelling) in adults
  20. 26. Lots of possible causes for hypothyroidism Lack of: thyrotropin-releasing hormone from hypothalamus insufficient TSH from pituitary iodine deficiency (goiter) Hyperthyroid Graves’ disease; tumors metabolic rate is too high irritability; intolerance of heat high blood pressure See Table 11.8 for comparison
  21. 28. Children with thyroxine deficiencies will lack normal gowth and nervous system development (cretinism) (lack of growth hormone does not affect intelligence) Immediate treatment with thyroxine will restore intelligence Children are now routinely tested at birth for thyroid function
  22. 29. Review other hormones for: where produced and what are target organs/tissues how regulated (feedback, pituitary, etc.) disorders associated with overproduction or underproduction

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