CALCIUM AND BONE Flashcards
Where is parathyroid hormone metabolised?
The kidney and liver
What is the half life of parathyroid hormone?
4 mins
What is the trigger for the release of parathyroid hormone?
A fall in plasma free ionised calcium
Rise in plasma phosphate (more chronic)
What are the key actions of parathyroid hormone? Name 4
Acts on kidney to promote calcium uptake
Promotes bone resorption by osteoclasts
Increases calcium uptake in the GI indirectly (by generating active vitamin D)
Promotes phosphate excretion in renal tubules
What type of hormone is vitamin D?
Steroid hormone
What are the forms of vitamin D measured in a blood test?
25-hydroxyvitamin D (2 and 3)
What are possible causes of vitamin D deficiency?
Lack of sunlight
Poor diet
Where is vitamin D activated? Name both organs
In the liver
In the kidney
What is the form of vitamin D metabolised in the kidney in step 2?
Calcitriol
What forms of vitamin D are normally given as supplements?
D2 and D3 (find names for these)
What percentage of the calcium in the circulation is ionised?
45%
What is the physiologically active form of calcium?
Ionised form
How are the other 55% (not ionised) of calcium circulating?
45% bound to albumin
10% complexed
What is the serum calcium result adjusted for?
Serum levels of albumin
What is the formula for working out the adjusted calcium result?
Adjusted calcium = total calcium + 0.02(40 - albumin)
What is the normal range for calcium?
2.2 - 2.6 mmol/L
How can you distinguish between a parathyroid induced hypercalcaemia and hypercalcaemia caused by something else?
If hypercalcaemic plus suppressed PTH then this is due to something else. If hypercalcaemic plus raised PTH then this is probably due to parathyroid.
What are PTH mediated causes of hypercalcaemia?
Calcium receptor defects
Primary or tertiary hyperparathyroidism
What is the most common cause of hypercalcaemia?
Hypercalcaemia of malignancy
What malignancies can cause hypercalcaemia?
Often bony metastases
What does primary hyperparathyroidism mean?
Adenoma or hyperplasia of parathyroid
What is secondary hyperparathyroidism?
Increased PTH due to lack of calcium. Could be as a result of renal failure or malabsorption.
What is tertiary hyperparathyroidism?
This is due to a prolonged secondary hyperparathyroidism where the underlying cause of the initial calcium decrease is successfully treated.
What are the most common causes of primary hyperparathyroidism?
Sporadic adenomas.
Also part of MEN type 1.
What are the common symptoms of primary hyperparathyroidism?
Fatigue
Weakness
Kidney stones occur in 20% of cases
Psychiatric symptoms (eg depression)
What is the treatment of primary hyperparathyroidism?
Surgical removal of the tumour.
How can you know if the surgery has been a success before the operation is even finished?
Because the half life of PTH is so short that you can assess whether there has been a 50% drop in PTH levels.
What are non-parathyroidal causes of hypocalcaemia?
Vitamin D deficiency
Renal failure
What are parathyroid causes of hypocalcaemia?
Magnesium defiency
Hypoparathyroidism
What markers can you look at to assess osteoblasts activity?
Alkaline phosphatase
Collagen peptides
What markers can we look at to assess osteoporosis?
There are no good markers as the ones that we do use all suffer from high intraindividual variation.
We can look at urine NTX, plasma CTX, P1NP
What are the systems involved in calcium homeostasis?
GI
Kidney
Skeleton
Parathyroid
