Calcium Dysregulation Flashcards
What is the key characteristic used to identify tertiary hyperparathyroidism?
Renal failure
What causes secondary hyperparathyroidism?
Vitamin D deficiency
What increase serum calcium?
- vitamin D (skin or diet)
- PTH (parathyroid glands)
via actions on: kidney, bone and gut
What decreases serum calcium?
- calcitonin (thyroid parafollicular cells)
can reduce calcium acutely, no negative effect if parsafollicular cells are removed
What is the active form iof vitamin D?
calcitriol
What is the relationship between 1,25(OH)2 vitamin D (calcitriol) and 1 alpha hydroxylase?
calcitriol regulates it’s own synthesis by decreasing transcription of 1 alpha hydroxylase
What are the effects of calcitriol?
bones: increased osteoblast activity
kidney: increased calcium and phosphate reabsorption
gut: phosphate and calcium reabsorption
What are the effects of PTH?
bone: increased calcium resorption from bone
(increased osteoclast activity)
kidney: increased calcium reabsorption, increased phosphate excretion and increased calcitriol synthesis.
gut: the increased calcitriol from the kidney’s effects mean increased calcium and phosphate reabsorption
What is the net effect of phosphate?
fairly neutral
Does PTH increase calcium?
yes
What is FGF23?
regulate phosphate
more FGF23, greater phosphate excretion
Where is FGF23 made?
osteocytes
How does FGF23 lower phosphate levels in the body?
- inhibits sodium/phosphate co-transporter, must be lost to the urine
- inhibits calcitriol formation, therefore less phosphate is reabsorbed.
What is the sodium/phosphate channel inhibited by?
- PTH
- FGF23
What is the effect of hypocalcaemia?
sensitisation of excitable tissues; muscle cramps, tetany and tingling
What are the signs/symptoms of hypocalcaemia?
- paraethesia
- convulsions
- arrhythmias
- tetany
- Chvosteks’ sign
- Trousseau’s sign
What is paraesthesia?
pins and needles in hands, mouth, feet…