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Parathyroid Hormone

Parathyroid Hormone

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Parathyroid Hormone

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  1. Parathyroid Hormone ENDO BLOCK 412 Dr. Shaikh Mujeeb Ahmed Assistant Professor AlMaarefa College

  2. Lecture Objectives • At the end of this lecture the student should be able to • Describe the role of calcium in the body • Enumerate the factors affecting plasma calcium • Describe the mechanisms controlling plasma Ca++ concentration • Describe the chemical nature, source and actions of parathyroid hormone • Describe the chemical nature, source and actions of calcitonin hormone • Describe the role of vit.D in regulation of Ca++ conc. • Describe Pathophysiology of hypo & hyperparathyroidism • Describe the effects of Vit.D deficiency

  3. Calcium Distribution

  4. Vital role of Ca++ • Neuromuscular excitability • Excitation contraction coupling in cardiac, smooth & skeletal muscle • Stimulus secretion coupling • Excitation secretion coupling • Maintenance of tight junctions between cells • Clotting of blood

  5. Endocrine Control of Calcium Metabolism • Three hormones regulate plasma concentration of Ca2+ (and PO43-) • Parathyroid hormone (PTH) • Calcitonin • Vitamin D

  6. Ca++ homeostasis & Ca++ balance • Ca++homeostasis • Ca++ adjustment on Minute to minute basis • Exchange between bone and ECF • Ca++ balance • Slowly responding adjustment • Ca++ intake VsCa++ excretion • Parathyroid hormone (PTH) the principal regulator of Ca++ metabolism , acts directly or indirectly on all three of these effector sites.

  7. Parathyroid hormone • secreted by the parathyroid glands, • four rice grainsized glands located on the back surface of the thyroid gland, one in each corner

  8. Cont… • PTH is essential for life • The overall effect is increase plasma Ca++ • Complete absence of PTH ensues death within few days. • It acts on bone, kidneys and intestine • PTH acts to lower plasma PO43- conc.

  9. PTH raises plasma Ca2+by withdrawing Ca2+from the bone bank. • induces a fast Ca2+ efflux into the plasma from the small labile pool of Ca2+in the bone fluid. • Second, by stimulating bone dissolution, it promotes a slow transfer into the plasma of both Ca2+and PO43-from the stable pool of bone minerals in bone itself.

  10. PTH’s chronic effect is to promote localizeddissolution of bone to release Ca2+into plasma. • Stimulate osteoclast • Both Ca2+ & PO43- are released in plasma • PTH deals with PO4 by its action on kidneys

  11. PTH acts on the kidneys to conserve Ca2+and eliminate PO43- • Absorb more Ca++ • Decrease reabsorption of PO43- • an inverse relationship exists between the plasma concentrations of Ca2+and PO43- • Activation of Vit. D • PTH indirectly promotes Ca++ & PO43- absorption from the intestine by helping Vit.D

  12. Regulation of PTH secretion • PTH secretion increases when plasma Ca2 falls and decreases when plasma Ca2 rises. • this relationship forms a simple negative- feedback loop for controlling PTH secretion

  13. Calcitonin • Polypeptide hormone produced by C cells of thyroid gland • Decreases plasma Ca++ levels • on a short-term basis calcitonin decreases Ca ++movement from the bone fluid into the plasma. • Second, on a long-term basis calcitonin decreases bone resorption by inhibiting the activity of osteoclasts via the cAMP pathway. • Calcitonin also inhibits Ca ++and PO43- reabsorption from the nephron

  14. ACTIONS OF CALCITONIN ON BONE • Decresaed osteoclastic number • Decreased osteoclastic activity • Actions are proportional to baseline rate of bone turnover

  15. VITAMIN D • cholecalciferol, or vitamin D, a steroid like compound essential for Ca++ absorption in the intestine. • Activated by the addition of two (-OH) groups. • The first reaction occurs in the liver & the second in kidneys. • The active form of vit.D is 1,25-(OH)2- vitamin D3 also known as calcitriol.

  16. Fig. 19-27, p. 736

  17. Disorder of parathyroid hormone • PTH hypersecretion – hyperparathyroidism • Characterized by hypercalcemia & hypophosphatemia • Clinical features: • Muscle weakness • Decrease alertness, poor memory & depression • Cardiac disturbances • Mobilization of Ca2+ & PO43- from skeletal store may results in thinning of bone, fractures, skeletal deformities • Increase incidence of Kidney stones

  18. Hyperparathyroidism • Bones • Stones • Abdominal groans

  19. PTH hyposecretion • Hypoparathyroidism • Inadvertent removal of parathyroid gland • Hypocalcemia and hyperphospatemia • Increased neuromuscular excitability • Muscle cramps twitches • Tingling and pins and needle sensation • Irritability & paranoia

  20. SIGNS AND SYMPTOMS OF HYPOPARATHYROIDISM • Positive Chvostek’s (facial muscle twitch) sign • Positive Trousseau’s (carpal spasm) sign • Delayed cardiac repolarization with prolongation of the QT interval • Paresthesia • Tetany

  21. Hypocalcemictetany

  22. VITAMIN D DEFICIENCY • Decrease Ca++ absorption from intestine. • PTH increases plasma Ca++ from bone • Demineralization of bones - softening • Rickets in children • Osteomalacia in adult.

  23. p. 730

  24. 1 1 1 1 1 1 3 3 3 3 High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. High level of Ca2+ in blood stimulates thyroid gland parafollicular cells to release more CT. Low level of Ca2+ in blood stimulates parathyroid gland chief cells to release more PTH. Low level of Ca2+ in blood stimulates parathyroid gland chief cells to release more PTH. Low level of Ca2+ in blood stimulates parathyroid gland chief cells to release more PTH. Low level of Ca2+ in blood stimulates parathyroid gland chief cells to release more PTH. 6 CALCITRIOL stimulates increased absorption of Ca2+ from foods, which increases blood Ca2+ level. 5 5 PTH also stimulates the kidneys to release CALCITRIOL. PTH also stimulates the kidneys to release CALCITRIOL. 4 4 4 2 2 2 2 2 PARATHYROID HORMONE (PTH) promotes release of Ca2+ from bone extracellular matrix into blood and slows loss of Ca2+ in urine, thus increasing blood Ca2+ level. PARATHYROID HORMONE (PTH) promotes release of Ca2+ from bone extracellular matrix into blood and slows loss of Ca2+ in urine, thus increasing blood Ca2+ level. PARATHYROID HORMONE (PTH) promotes release of Ca2+ from bone extracellular matrix into blood and slows loss of Ca2+ in urine, thus increasing blood Ca2+ level. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca2+ level. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca2+ level. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca2+ level. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca2+ level. CALCITONIN inhibits osteoclasts, thus decreasing blood Ca2+ level.

  25. References • Human physiology, Lauralee Sherwood, seventh edition. • Text book physiology by Guyton &Hall,11th edition. • Text book of physiology by Linda .S .Costanzo third edition