8.3 Vitamin D (Calcium Role) — RBR Life Science

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8.3 Vitamin D (Calcium Role) — Test 1

Q1. The active form of vitamin D, 1,25-dihydroxycholecalciferol, primarily increases:✓ Intestinal calcium (and phosphate) absorption

Q2. The final activating hydroxylation of vitamin D occurs in the:✓ Kidney (1alpha-hydroxylase)

Q3. Renal 1alpha-hydroxylase is stimulated by:✓ PTH, low calcium and low phosphate

Q4. Vitamin D deficiency in children causes:✓ Rickets

Q5. Vitamin D deficiency in adults causes:✓ Osteomalacia

Q6. Unlike PTH, the net effect of vitamin D on phosphate is to:✓ Increase phosphate absorption (raising phosphate)

Q7. Match each compound with its description and choose the correct option.✓ A-iii, B-ii, C-i

Q8. Vitamin D acts on its target cells by a mechanism resembling that of:✓ Steroid hormones (intracellular/nuclear receptor)

Q9. In chronic renal failure, impaired 1alpha-hydroxylation leads to:✓ Low active vitamin D, hypocalcemia and secondary hyperparathyroidism

Q10. The gut protein induced by vitamin D to carry calcium is:✓ Calbindin

Q11. The 25-hydroxylation of vitamin D occurs in the:✓ Liver

Q12. High serum phosphate tends to:✓ Inhibit 1alpha-hydroxylase (lowering active vitamin D)

Q13. Vitamin D, calcium and PTH together act to:✓ Maintain plasma calcium and bone mineralization

Q14. Which vitamin is considered to act as a hormone?✓ Vitamin D

Q15. Rickets is characterised by:✓ Defective mineralization of growing bone

Q16. The cutaneous synthesis of vitamin D requires:✓ UV light acting on 7-dehydrocholesterol

Q17. Active vitamin D also has a small direct effect on bone, promoting:✓ Normal mineralization (and supporting resorption with PTH)

Q18. Secondary hyperparathyroidism in vitamin D deficiency occurs because:✓ Low calcium (from poor absorption) drives PTH up

Q19. Compared with PTH, vitamin D acts:✓ More slowly, mainly via increased gut absorption

Q20. In renal osteodystrophy, the underlying hormonal disturbance includes:✓ Low active vitamin D with secondary hyperparathyroidism