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Calcium metabolism and vitamin D
- 1. Calcium metabolism and Vitamin D Dr. Sairamakrishnan S
- 2. • Blood calcium is tightly regulated • Principle organ systems – Intestines, bone, kidneys • Hormones – Parathyroid hormone (PTH), Vitamin D, Calcitonin • Integrated physiology of organ systems and hormones maintain blood calcium
- 3. Intake 1000 mg/day Feces 900 mg/day Cells 13,000 mg Urine 100 mg/day Extracellular fluid 1300 mg Bones 10,00,000 mg Absorption 350mg/day Secretion 250mg/day Resorption 500mg/day Deposition 500mg/day Filtration 9980mg/day Resorption 9880mg/day
- 4. • Functions of Calcium – Bone mineralisation – Activation of clotting factors – Muscle contraction – Co-factor in enzymatic reactions – Nerve conduction – Cardiac function
- 5. 7-dehydrocholesterol Pre vitamin D3 Vitamin D3 UVB Rays Skin Blood vessel Lipoproteins Vit.D Binding Protein Vitamin D
- 6. Vitamin D 25 hydroxylase 25-OH(Vit-D) 25-OH(Vit-D) 1 hydroxylase 1,25-OH(Vit-D) 25-OH(Vit-D) 1,25-OH(Vit-D)
- 8. • Bone turnover: a coupled process of bone formation and bone resorption (break down) – Takes place throughout life – Shift toward formation or resorption causes alteration in bone mass
- 9. • Skeletal mass in the human reaches a peak at about age 30 – Prior to that, as skeletal mass is increasing, bone formation exceeds bone resorption. – At peak bone mass, the two processes are exactly matched – After the age of peak bone mass, skeletal mass is lost for the rest of life
- 10. • 1,25(OH)VitD production • Tubular response (Ca reabsorption) • 1,25(OH)VitD supplementation in renal insufficiency/failure
- 11. • Vitamin D and PTH are interregulated – Vitamin D inhibits PTH production
- 12. • Normal intestinal function and normal response to vitamin d are required for normal calcium absorption. – Increases intestinal absorption
- 15. Calcitonin
- 16. Hypercalcemia • Signs and symptoms depend on the degree of hypercalcemia and comorbid conditions – There is no absolute value of blood calcium at which symptoms develop. – Level of blood calcium at which symptoms develop vary from patient to patient.
- 17. Causes of hypercalcemia • Hormonal – Primary hyperparathyroidism – Hypervitaminosis D • Non-hormonal – Renal failure – Milk-alkali syndrome • Drugs – Thiazides, lithium, others
- 18. Hypercalcemia: signs and symptoms • CNS: altered behavior, including lethargy, depression, decreased alertness, confusion, obtundation, and coma • GI: anorexia, constipation, nausea, and vomiting • RENAL: diuresis, impaired concentrating ability, dehydration. Hypercalciuria is a risk for kidney stones. • SKELETAL: most causes of hypercalcemia are associated with increased bone resorption, and thus, fracture risk • CARDIOVASCULAR: cause/exacerbate HTN
- 19. Hypocalcemia • The state of blood calcium below the normal range – Most accurately assessed with ionized calcium – Total calcium cannot be accurately interpreted without knowing serum albumin – Fairly uncommon
- 20. Causes of hypocalcemia • Hypoparathyroidism – Postsurgical (most common) – Autoimmune – Pseudohypoparathyroidism (PTH resistance) – Idiopathic • Hypovitaminosis D – Dietary Deficiency – Rickets, Osteomalacia • Organ Dysfunction – GI malabsorption, Renal loss
- 21. Hypocalcemia: signs and symptoms • Neuromuscular: involuntary muscle contraction (tetany), 7th cranial nerve excitability (Chvostek’s sign), numbness and tingling in face, hands, and feet, Trousseau’s sign • CNS: irritability, seizures, personality change, impaired cognition • Cardiovascular: QT prolongation on ECG, in the extreme, electromechanical dissociation may occur