CALCIUM AND PHOSPHATE HOMEOSTASIS Organs Parathyroid Four oval

Parathyroid • Four oval masses on posterior of thyroid gland • Develops from the

Parathyroid hormone (PTH) • Protein/peptide • Metabolized in liver and kidney • Receptor: G

Thyroid (Parafollicular cells) • Cells located outside thyroid follicles • Derived embryonically from the

Vitamin D • Sterol hormone • Production requires several organs • Production: – 7

Parathyroid hormone (PTH) • Increases serum Ca++ concentration • Kidney – Ca++ reabsorption –

Calcitonin • • • Decreases serum Ca++ concentration Bone Kidney Question of its physiological

Dihydroxy-Vitamin D • Increases intestinal absorption of Ca++ • Stimulate bone matrix protein production

Regulation of PTH SERUM Ca++ REABSORPTION CHIEF CELL OF PARATHYROID PTH KIDNEY VIT. D

Regulation of Calcitonin SERUM Ca++ REABSORPTION THYROID PARAFOLLICULAR CELLS CT KIDNEY CT BONE DISTAL

Regulation of Vitamin D UV LIGHT TANNING SERUM PHOSPHATE SKIN CHOLECALCIFEROL 1, 25 -OH-D

Regulation of Ca++ REABSORPTION SERUM Ca++ OSTEOCLAST KIDNEY BONE PTH PARATHYROID GLAND SERUM Ca++

Other Hormones ++ Affecting Ca • Estrogen – Inhibits Osteoclasts – Stimulates Calcitonin –

Pathologies • Hypercalcemia – Hyperparathyroidism • Hypocalcemia – Hypoparathyroidism • Osteoporosis – Role of

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CALCIUM AND PHOSPHATE HOMEOSTASIS

Organs:

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

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

Thyroid (Parafollicular cells) • Cells located outside thyroid follicles • Derived embryonically from the ultimobranchial body • Make up about 0. 1% of the mass of the thyroid • Calcitonin – 32 -amino acid peptide

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

Actions of the Hormones

Parathyroid hormone (PTH) • Increases serum Ca++ concentration • Kidney – Ca++ reabsorption – phosphate reabsorption • Bone • Intestine

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

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

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

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

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

Regulation of Ca++ REABSORPTION SERUM Ca++ OSTEOCLAST KIDNEY BONE PTH PARATHYROID GLAND SERUM Ca++ 4. 64 -5. 28 mg/dl ++ Ca PARAFOLLICULAR CELLS CT BONE CT KIDNEY OSTEOCLAST OSTEOBLAST SERUM Ca++ REABSORPTION

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

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