Controllo endocrino del metabolismo del calcioCATTEDRA DI FISIOLOGIA
Prof. Giuseppe Cibelli
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
- Parathyroid Hormone
- Actions
Calcitonin
Osteoporosis
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
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
Distribuzione intracellulare del Calcio
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
Funzioni del Ca++ e del Pi
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
Controllo ormonale del metabolismo del of Ca++
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
Effetti metabolici del paratormone
Metabolismo della vitamina D
Formazione e azione del calcitriolo
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
Azioni della calcitonina
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
Comments