Discuss the role of vitamin D in bone metabolism

Question 1

What is calcidiol?

Answer 1

the storage form of vitamin D in the body

Question 2

Where is calcidiol (25OHD) converted into calcitriol (1,25(OH)₂D)?

Answer 2

The kidney

Question 3

How is calcium found in plasma?

Answer 3

• 50% protein bound (albumin)
• 50% ionised

Question 4

What cardiac abnormalities are associated with hypocalcaemia?

Answer 4

• arrhythmias
• hypertrophy
• hypotension
• failure

Question 5

What does a plasma 25(OH)D level 25-50 nmol/L indicate?

Answer 5

inadequate vitamin D levels in some people

Question 6

What is calcitriol?

Answer 6

The active form of vitamin D in the body

1,25-dihydroxy vitamin D

Question 7

How does a vitamin D deficiency affect calcium levels?

Answer 7

Vit D deficiency causes low calcium absorption

Question 8

What condition can be caused by either a calcium or vitamin D deficiency?

Answer 8

hyperparathyroidism

Question 9

What is 25-hydroxyvitamin D (25(OH)D)

Answer 9

an integrated marker of vitamin D supply (skin, diet, reserved)

Question 10

What does a plasma 25(OH)D concentration of > 50 nmol/L indicate?

Answer 10

sufficient vitamin D levels

Question 11

What physical features of bone is attributable to calcium?

Answer 11

stiffness and structure

Question 12

What regulatory functions is calcium involved in?

Answer 12

• neurotransmission
• reproduction
• hormone action
• cellular growth
• enzyme function

Question 13

What is hydroxyapatite Ca₁₀(PO₄)₆(OH)₂

Answer 13

A ceramic material which forms the mineral phase of bone

Question 14

What are 5 causes of vitamin D deficiency?

Answer 14

1. low sunshine exposure
2. low dietary supply
3. low absorption (GI disorders w/ fat malabsorption)
4. obesity
5. high loss and/or utilisation

Question 15

What is rickets disease?

Answer 15

the failure or delay in endochondral calcification at the growth plates of long bones in children

Question 16

What are 3 clinical symptoms of a vitamin D deficiency in children?

Answer 16

1. bone deformities
2. cardiac problems
3. hypocalcaemic fits

Question 17

What factors can affect the amount of calcium absorbed by the body?

Answer 17

• vitamin D status + active vitamin D
• age (postmenopausal women down 0.21%)
• bioavailability (milk, beans, spinach)
• GI disorders

Question 18

Who are at an increased risk of low 25(OH)D? (5)

Answer 18

• dark skinned people
• renal disease
• GI disorders
• frail elderly
• those who get little UVB exposure

Question 19

What is calcium homeostasis controlled by?

Answer 19

• PTH
• calcitonin
• active vitamin D 1,25(OH)₂D

Question 20

What plasma concentration of 25(OH)D indicates a vitamin D deficiency?

Answer 20

< 25 nmol/L

Question 21

What does an albumin adjusted calcium > 2.6 mmol/L indicate?

Answer 21

hypocalcaemia

Question 22

What are 6 clinical symptoms of vitamin D deficiency?

Answer 22

• non-specific
• fatigue
• generalised muscle, joint, bone pain
• hyperalgesia (increased sensitivity to pain)
• muscle weakness
• fragility fractures

Question 23

What does the concentration of 25-hydroxyvitamin D reflect?

Answer 23

the balance of vitamin D intake and expenditure

Question 24

What are 7 signs of hypocalcaemia?

Answer 24

1. paraesthesia
2. muscle spasms/tetany
3. cardiac abnormalities
4. coma
5. nausea
6. pelptic ulcers
7. renal stones/failure
   8.

Question 25

What are 6 sources of vitamin D?

Answer 25

• skin synthesis of summer sun
• oily fish
• meat
• eggs
• fortified spreads
• fortified cereals

Question 26

What is osteomalacia a result of?

Answer 26

defective mineralisation of preformed osteoid

Question 27

What does intestinal calcium absorption depend on?

Answer 27

• calcium intake
• active absorption
• life stage
• physiological state (growth, pregnancy, lactation)

Question 28

What is calciferol?

Answer 28

The supply of vitamin D