The Endocrine System


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The Endocrine System

  1. 1. The Endocrine System Chp. 6 <ul><li>Primary endocrine organs: main function is to secrete hormone(s) </li></ul><ul><li>Secondary endocrine organs: secrete hormones as a secondary function </li></ul>
  2. 2. Primary endocrine organs <ul><li>Hypothalamus and pituitary gland secrete hormones and regulate other endocrine organs. They are the main regulatory organs of the endocrine system. </li></ul>
  3. 3. Hypothalamus <ul><li>Located below the thalamus and above the pituitary gland (=epiphysis) </li></ul><ul><li>Regulates the pituitary gland secretions through two different mechanisms </li></ul>
  4. 4. Hypothalamus - neurohypophysis <ul><li>1- Neurons, receiving information from receptors, fire APs which travel down to the post pituitary gland and stimulate the release of stored neurohormones – Oxytocin (OT) and anti-diuretic hormone (ADH) </li></ul>
  5. 5. Hormones of the posterior pituitary - not enough: diabetes insipidus - too much: ↑ BP? - promote H2O reabsorption - DCT in kidney tubules ADH (vasopressin) Reflex (osmoreceptor) -- -- <ul><li>labor and delivery </li></ul><ul><li>- milk-let down </li></ul>- Uterus (smooth muscle) - breast tubules (smooth muscles) Oxytocin Reflex Pathology Action Target organ Hormone Regulation
  6. 6. Hypothalamus – adenohypophysis <ul><li>2- Upon stimulation, secretory cells located in the hypothalamus secrete “releasing” hormones which travel down a capillary bed toward the anterior pituitary gland (adenopituitary). Each type of releasing hormones will stimulate the secretion and release of a pituitary hormone. </li></ul><ul><li>Hormones which control the secretion of other hormones are tropic hormones (found in hypothalamus and pituitary gland </li></ul>
  7. 7. Hormones of the hypothalamus and anterior pituitary gland Figure 6.5
  8. 8. Figure 6.8 Anterior pituitary - infertility Stimulate gonadal gland secretion and gamete formation Stimulate gamete maturation Gonadotropin - Follicle stimulating hormone (FSH) - Luteinizing hormone (LH) GnRH - not enough: Addison's disease - too much: Cushing syndrome - stimulates secretion of adrenal cortex Adrenal cortex (3 layers) Adrenocorticotropic hormone (ACTH) CRH - not enough: hypothyroidism (cretinism in children) - too much: hyperthyroidism - promote thyroid gland secretion (T3 and T4) Thyroid gland Thyroid stimulating hormone (TSH) TRH -- - milk secretion Breast secretory cells Prolactin (PL) PRH - PIH - not enough: children  pituitary dwarfism too much: gigantism (children) – acromegaly (adult) Stimulate cell growth and cell division Many cells (bones..) Growth hormone (GH) GHRH and GHIH Pathology Action Target organ Hormone Regulation
  9. 9. Same Individual with Acromegaly (evolution over 20 years) Figure 23-17
  10. 10. Mechanism of control Figure 6.6
  11. 11. The thyroid gland - Chp 21 p 623-625 <ul><li>Located in the neck, just below the larynx </li></ul><ul><li>Secrete 2 types of hormone: </li></ul><ul><li>- thyroid hormones  stimulate cell metabolism, triiodothyronine (T3) and thyroxine (T4) – iodine is needed to synthesize these hormones </li></ul><ul><li>- calcitonin  decrease blood calcium </li></ul>Figure 6.8a
  12. 12. Thyroid hormones <ul><li>T3 and T4 secreted by the follicular cells </li></ul><ul><li>Stored as colloid </li></ul><ul><li>Parafollicular cells (C cells) secrete calcitonin (Chp 19) </li></ul>
  13. 13. Thyroid Hormones T3 and T4 <ul><li>Target organs: all cells </li></ul><ul><li>Role: Increase cell metabolism, oxygen consumption </li></ul><ul><li>Permissive role for some other hormones (growth hormone) </li></ul>
  14. 14. Thyroid hormone regulation Figure 6.7
  15. 15. Goiter <ul><li>Both hypo and hyperthyroidism can have goiter as a symptom </li></ul><ul><li>Goiter is a swelling of the neck due to hypertrophy of the thyroid gland </li></ul><ul><li>How can one explain that? </li></ul>
  16. 16. Goiter in hypothyroidism <ul><li>Most often due to a lack of dietary iodine </li></ul><ul><li>The thyroid hormone is unable to synthesize a functional thyroid hormone (T3 and T4) </li></ul><ul><li>The person express symptoms of hypothyroidism </li></ul><ul><li>The nonfunctional T3/T4 cannot promote a negative feedback on TRH and TSH </li></ul><ul><li> the hypotalamus and pituitary gland increase their secretions  the thyroid gland is stimulated to secrete more T3 and T4 … </li></ul><ul><li>In children, the lack of functional T3/T4 result in cretinism, a form a mental retardation </li></ul>
  17. 17. Goiter in hyperthyroidism <ul><li>The cells secreting TRH or TSH on the hypothalamus and pituitary gland (respectively) have become abnormal and no longer are sensitive to the negative feedback  they continue to secrete TRH or TSH  continuous stimulation of the thyroid gland with excess thyroid hormones being formed </li></ul><ul><li> symptoms of hyperthyroidism </li></ul>
  18. 18. Parathyroid glands <ul><li>Four nodules located in the back of the thyroid gland </li></ul><ul><li>Secreted parathyroid hormone or parathormone or PTH </li></ul><ul><li>Action of PTH opposes action of calcitonin </li></ul><ul><li>Both hormones play a role in calcium metabolism </li></ul>
  19. 19. Roles of calcium <ul><li>Most calcium ions are stored in the bones </li></ul><ul><li>Calcium is an important cofactor for enzymatic activity, plays a role in blood coagulation and action potentials. </li></ul><ul><li>Calcitonin and PTH participate in calcium regulation </li></ul><ul><li>Vitamin D helps PTH activity </li></ul>
  20. 20. Calcium regulation: <ul><li>Calcitonin promotes blood calcium decrease, by: </li></ul><ul><li>1. calcium deposition on bone </li></ul><ul><li>2. calcium dumping by the kidney </li></ul><ul><li>PTH promotes blood calcium increase by: </li></ul><ul><li>1. bone resorption </li></ul><ul><li>2. calcium reabsorption by kidney </li></ul><ul><li>3. increase calcium absorption by intestine </li></ul>
  21. 21. Calcium Metabolism: Figure 23-20: Calcium balance in the body
  22. 22. Figure 19.20
  23. 23. The adrenal glands <ul><li>Two endocrine glands: </li></ul><ul><li>1- Adrenal medulla: an extension of the sympathetic ANS  cell secrete epinephrine </li></ul><ul><li>2- Adrenal cortex: 3 layers with 3 different hormones </li></ul>
  24. 24. Figure 6.12b
  25. 25. Figure 21.15
  26. 26. Adrenal gland hormones Infertility - Sex organ maintenance - Gamete development Sexual organs Estrogen Testosterone GnRH  GN Excess hormone: Cushing syndrome Mobilize fuels – stress adaptation Many cells Glucocorticoid = cortisone CRH  ACTH Not enough&quot; Addison disease - promote sodium reabsorption DCT from renal tubule - Mineralocorticoid = aldosterone Adrenal cortex Blood Pressure Stress Fight/flight ANS target organs Epinephrine Adrenal medulla Reflex Pathology Action Target organs Hormones Glands Regulation
  27. 28. The pancreas <ul><li>Located in the left upper abdominal cavity </li></ul><ul><li>Exocrine and endocrine glands </li></ul><ul><li>The endocrine function is due to the cells of the islets of the Langerhans </li></ul><ul><li>-- α cells  glucagon </li></ul><ul><li>-- β  insulin </li></ul><ul><li>-- δ  somatostatin </li></ul>
  28. 29. Glucose regulation <ul><li>Glucose level controlled by insulin and glucagon </li></ul><ul><li>Insulin promotes a decrease in blood glucose </li></ul><ul><li>Glucagon promotes an increase in blood glucose </li></ul>
  29. 30. Glucose regulation
  30. 31. Fate of glucose Figure 3.21
  31. 32. Diabetes mellitus <ul><li>Type I: autoimmune disease  beta cells of the islets of Langerhans are destroyed by antibodies </li></ul><ul><li>Type II: The cells become insulin-resistant  glucose does not enter the cells as readily </li></ul><ul><li> </li></ul>
  32. 33. Diabetic foot