1. CALCIUM AND PHOSPHATE HOMEOSTASIS

2. Organs:

3. Parathyroid Four oval masses on posterior of thyroid gland Develops from the 3 rd and 4 th pharyngeal pouches Cell Types –Chief –Oxyphil

4. Parathyroid hormone (PTH) Protein/peptide Metabolized in liver and kidney Receptor: G protein associated receptor

5. Thyroid (Parafollicular cells) Cells located outside the thyroid follicles Derived embryonically from the ultimobranchial body Make up about 0.1% of the mass of the thyroid Calcitonin –32-amino acid peptide

6. Vitamin D Sterol hormone Production requires several organs Production: –7-dehydrocholesterol –Cholecalciferol –25 Hydroxy Cholecalciferol –1,25-Dihydroxy Cholecalciferol No dietary source of Vitamin D 3 Binds to an intracellular receptor

7. Actions of the Hormones

8. Parathyroid hormone (PTH) Increases serum Ca ++ concentration Kidney –  Ca ++ reabsorption –  phosphate reabsorption Bone Intestine

9. Calcitonin Decreases serum Ca ++ concentration Bone Kidney Question of its physiological role Clinical usefulness

10. Dihydroxy-Vitamin D Increases intestinal absorption of Ca ++ Stimulate bone matrix protein production by osteoblasts Activate osteoclasts Increase phosphate reabsorption by kidney Maintain Ca ++ reabsorption by the kidney Inhibits PTH production & secretion

11. Regulation of PTH CHIEF CELL OF PARATHYROID SERUM Ca ++ BONE OSTEOCLASTS KIDNEY DISTAL C T SERUM Ca ++ PTH Ca ++ RELEASE Ca ++ REABSORPTION PTH VIT. D

12. Regulation of Calcitonin THYROID PARAFOLLICULAR CELLS SERUM Ca ++ BONE OSTEOCLASTS KIDNEY DISTAL C T SERUM Ca ++ CT Ca ++ RELEASE Ca ++ REABSORPTION CT

13. Regulation of Vitamin D SKIN UV LIGHT LIVER KIDNEY CHOLECALCIFEROL 25-OH-D 3 PTH GH/PRL ESTROGEN 1,25-OH-D 3 SERUM PHOSPHATE TANNING

14. Regulation of Ca ++ SERUM Ca ++ 4.64-5.28 mg/dl SERUM Ca ++ SERUM Ca ++ BONE KIDNEY PARAFOLLICULAR CELLS CT  Ca ++ REABSORPTION  OSTEOCLAST  OSTEOBLAST PARATHYROID GLAND PTH  Ca ++ REABSORPTION  OSTEOCLAST

15. Other Hormones Affecting Ca ++ Estrogen –Inhibits Osteoclasts –Stimulates Calcitonin –Stimulates Vitamin D GH/IGF-1 Glucocorticoids Thyroid Hormone

16. Pathologies Hypercalcemia –Hyperparathyroidism Hypocalcemia –Hypoparathyroidism Osteoporosis –Role of estrogen Paget’s Disease Osteomalacia Rickets