Calcium and phosphate metabolism

Question 1

What’s osteoporosis?

Answer 1

= loss of bone mass due to renal disease, age, endocrine, nutritional

Diagnosis - measure of bone mineral density

Dual-energy C-ray absorptiometry

• T-score - number of SDs below average for young adult at peak bone density
• Z-score - matched to age and/or group

Question 2

What are the encodrine causes of osteoporosis?

Answer 2

Hypogonadism - any cause of oestrogen deficiency

Excess glucocorticoids - endogenous or exogenous

Hyperparathyroidism

Hyperthyroidism

Question 3

How does bone density vary at different ages in women?

Answer 3

Question 4

What are the treatments for osteoporosis?

Answer 4

• Ensure adequate calcium and vitamin D intake, appropriate exercise
• Postmenopausal - HRT
• Bisphosphonates - inhibit functions of osteoclasts

Question 5

What is osteomalacia?

Answer 5

= loss of bone mineralization (rickets)

Causes:

• Vitamin D deficiency
• Mutations leading to errors in vitamin D metabolism
• Hypophosphatemia

Question 6

What are the signs and symptoms of osteomalacia?

Answer 6

• Permanent deformities in bone growth
• Diffuse aches and pains
• Low Ca, Pi
• Elevated alkaline phosphatase
• PTH could be elevated

Question 7

Why is hypocalcaemia a hallmark for osteomalacia?

Answer 7

Main role of vitamin D is to promote calcium and phosphate absorption from the gut

Question 8

How can you regulate vitamin D?

Answer 8

The reaction from vitamin D to calcitriol is increased by:

• PTH
• Low Ca
• Low Pi

And decreased by:

• FGF-23
• High Ca
• High Pi

Question 9

What is renal osteodystrophy?

Answer 9

= spectrum of conditions associated with bone lesions in renal failure

• If renal is failing –> impaired phosphate excretion
• So you will have high plasma phosphate
• Impaired Vat D activation reaction - reduce calcitriol levels
• Leads to low plasma Ca
• PTH will rise
• Excess bone resorption = bone damage