Calcium

Question 1

Calcium normal range

• % free
• % bound & to what protein?
• What is adjusted Ca?

Answer 1

2.2 - 2.6 mmol/l

• 50% free
• 40% bound to albumin; so pathology that results in low albumin e.g. cirrhosis would give low total Ca - so we give adjusted Ca

Question 2

Ca metabolism is regulated by 2 hormones:

1. PTH - actions (3)
2. 1,25 (OH)₂ D = Vit D = calcitriol; actions (2)

Answer 2

PTH - released in response to low Ca

1. Increased Bone resorption
2. Increased kidney resorption + also PO4 excretion
3. Increased activation of 1a hydroxylase (activates 25 OH D > 1,25 (OH)₂ D)

Calcitriol/vit D

1. increased Ca2+ & PO4- absorption from gut
2. bone remodelling

Question 3

Describe the pathway of Vit D synthesis from 7-dehydrocholesterol. Include where required enzymes are made.

1. What is the plant version of cholecalciferol?
2. in which pathological condition can you get ectopic release of 1 alpha hydroxylase - thereby disrupting calcium metabolism?

Answer 3

Ergocholecalciferol

In Sarcoidosis can get release of 1 alpha hydroxylase from sarcoid lung cells > hypercalcaemia

Question 4

What is renal osteodystrophy?

Answer 4

Bone disease as a result of Vit D deficiency secondary to Renal pathology (unable to synth 1alpha hydroxylase > low vit D activation)

Question 5

• What is osteomalacia a result of?
• RFs for osteomalacia (4)
• clinical features (2)
• Biochemistry
• x-ray change (1)

Answer 5

1. Vit D def
2. Low sunlight exposure, low dietary intake, malabsorption, renal pathology (also pregnancy - placenta releases PTHrp to steal Ca from mother for fetal skeleton)
3. Bone & muscle pain (because osteoblasts trying to increase bone formation- releasing ALP, and osteoclasts increasing resorption)
4. Biochem - raised ALP, low Ca, low PO4, High PTH
5. Looser’s zone - pseudofractures (confirms low vit D and osteomalacia)

Question 6

Osteoporosis: what is it?

• 1st presentation?
• biochem?
• RFs (4)
• Dx (1)

Answer 6

Decreased bone density

• Fracture - usually low impact
• All normal
• RFs - immobile (which results in bone loss), increased age, post menopausa, Cushings & Hyperthyroidism
• Dx - T<2.5 (if between 1-2.5 is osteopenia)

Question 7

Osteoporosis management:

Lifestyle (2)

Drugs (3)

Answer 7

Lifestyle

• Weight loss, increase activity
• smoking cessation

Drugs

• Bisphosphonates e.g. alendronate (forms Cabisphosphate instead of CaPO4 which is not resorped by PTH action)
• Vit D
• Serms

Question 8

Primary HyperPTH

• what is the defect? (1)
• Biochem - Ca, PO4, PTH, ALP, Vit D

Answer 8

increased PTH - 80% due to parathyroid adenoma

• Ca high
• phosphate low
• PTH - norm/high
• ALP - norm/ high (remember ALP released due to osteoblast activity)
• Vit D - Normal

Question 9

Secondary hyperPTH

what is the defect? (1)

Biochem - Ca, PO4, PTH, ALP, Vit D

Answer 9

renal osteodystrophy

• Ca - low/norm (due to shitty renal function)
• PO4 - high
• PTH - high
• ALP - high
• Vit D - normal

(think of it is partially compensated)

Question 10

Tertiary HyperPTH

what is the defect? (1)

Biochem - Ca, PO4, PTH, ALP, Vit D

Answer 10

autonomous PTH secretion due to chronic renal disease (post transplant pts will have it)

• Ca - high
• PO4 - low
• PTH - high
• ALP - normal/high
• vit D - normal

(main difference is PO4 is low here but high in 2ndary PTH)

Question 11

Hypoparathyroidism

what is the defect? (1)

Biochem - Ca, PO4, PTH, ALP, Vit D

Answer 11

Low PTH - primary = Di george, secondary = post thyroid surgery

• Ca - low
• PO4 - high
• PTH - low
• ALP - low/norm
• Vit D - normal