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Controllo endocrino del metabolismo del calcio

Controllo endocrino del metabolismo del calcio. CATTEDRA DI FISIOLOGIA Prof. Giuseppe Cibelli. Outline. Calcium homeostasis - Importance of ionized calcium - Skeletal role Hormonal Control - Parathyroid Hormone - 1,25-(OH)2 Vitamin D3 - Calcitonin Parathyroid Glands

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Controllo endocrino del metabolismo del calcio

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  1. Controllo endocrino del metabolismo del calcio CATTEDRA DI FISIOLOGIA Prof. Giuseppe Cibelli

  2. Outline • Calcium homeostasis - Importance of ionized calcium - Skeletal role • Hormonal Control - Parathyroid Hormone - 1,25-(OH)2 Vitamin D3 - Calcitonin • Parathyroid Glands - Parathyroid Hormone - Actions • Calcitonin • Osteoporosis

  3. Omeostasi del Calcio • calcium, magnesium and phosphate homeostasis is essential for health and life. • Calcium is strictly regulated so that: intake = output (1000 mg ingested daily = l000 mg excreted daily) • extracellular calcium concentration [Ca++]ECF is maintained within narrow limits • normal range plasma calcium = 8.5 to 10.5 mg/dL • 50% free; 40% protein bound; 10% ion complexes

  4. Importanza funzionale del Calcio • need to control [Ca++]ECF reflects vital physiological functions of ionized (free) calcium including: - membrane function - neuromuscular function - intracellular signal transduction - enzyme reactions - blood coagulation - protein secretion - mineralization of bone

  5. Distribuzione intracellulare del Calcio

  6. Depositi del Calcio • adults have a total Ca++ body content of 1000-1500 grams and 500 grams phosphorus as phosphate • 1% of calcium found in blood, ECF and soft tissues (cells have Ca++-ATPase pump to extrude Ca++) • 99% of body calcium deposited in bone and teeth (0.5% readily exchangeable with ECF) • skeleton is storage depot for calcium and phosphate

  7. Funzioni del Ca++ e del Pi

  8. Controllo ormonale three hormones participate in the regulation of [Ca++]ECF • Parathyroid hormone PTH is produced by chief cells in the parathyroid gland (PTH is a protein hormone 84 amino acids in length) • 1,25-(OH)2 Vitamin D3 metabolite of Vitamin D (a sterol) formed in skin in response to UV light or present in diet. Vitamin D is metabolized in liver to 25-(OH) Vitamin D2 which is metabolized in kidneys to 1,25-(OH)3 Vitamin D3 (active hormone) • Calcitonin peptide produced by parafollicular cells located within the Thyroid Gland

  9. Controllo ormonale del metabolismo del of Ca++

  10. Paratiroidi • located on the posterior surface of the Thyroid Gland (usually 4 parathyroids,but more can be present) • Parathyroid Hormone - secretion stimulated by decreased [Ca++]ECF - secretion inhibited by increased [Ca++]ECF • Actions. Biological effects achieved by both indirect and direct actions: - Indirect actions include increased intestinal absorption of Ca++: 1,25-(OH)2 Vitamin D3 stimulates GI absorption of Ca++ - Direct actions include: - stimulation of renal formation of 1,25-(OH)2 Vitamin D3 (PTH increases renal 1-alpha-hydroxylase activity) - ncreased renal reabsorption of calcium - decreased renal reabsorption of phosphate - increased renal secretion of phosphate - bone resorption • NET EFFECT = INCREASED [Ca++]ECF

  11. Effetti metabolici del paratormone

  12. Metabolismo della vitamina D

  13. Formazione e azione del calcitriolo

  14. Calcitonina • secretion stimulated by increased [Ca++]ECF • secretion inhibited by decreased [Ca++]ECF • Actions: opposes the effects of parathyroid hormone: - decreases calcium movement from bone to plasma - decreases bone resorption • primary role in fetal and early development

  15. Azioni della calcitonina

  16. Osteoporosi • demineralization of bone • Aging: associated with demineralization-immune mediated? (macrophages produce 1,25-(OH)2 Vitamin D3) • Menopause: decreased estrogen production associated with increase bone resorption: - anti-PTH effect of estrogen - therapy: estrogen replacement - calcium - exercise

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