1b Calcium Dysregulation Flashcards
What are the two hormones which control serum calcium?
Vitamind D and Parathyroid hormone
What are the three places in which the regulators of serum calcium act?
Kidney, bone and the gut
What hormone acts to decrease serum calcium?
Calcitonin
Where is calcitonin secreted from?
The thyroid parafollicular cells
What effect does calcitonin have on serum calcium?
Reduces calcium acutely - however no negative effect if the parafollicular cells are removed eg thyroidectomy
What is tested for when a patients vitamin D levels are measured?
Serum 25-OH Vitamin D
How does calcitriol regulate its own synthesis?
it decreases transcription of 1-alpha hydroxylase
Describe how calcitriol is produced?
UVB from sun
7 dehydrocholesterol
Pre-vitamin D3 to Vitamin D3
D3 converted to 25 (OH) Cholecalciferol
Then to 1,25 (OH)2 cholecalciferol
Where is 25 hydroxylase found?
Liver
Where is 1-alpha hydroxylase found?
In the kidney
Which form of vitamin D is found in the diet?
D2
What are the effects of calcitriol on the kidneys?
Increased calcium and Phosphate reabsorption
What are the effects of calcitriol on the gut?
Increased phosphate and calcium absorption
What are the effects of calcitriol on the bone?
Increased osteoblast activity - bone building
What are the effects of PTH on the kidney?
Increased Calcium reabsorption and phosphate excretion and 1-alpha hydroxylase activity
What impact does PTH have on the gut?
The increased 1-alpha hydroxylase activity leads to more vitamin D, therefore more calcium and phosphate absorption
What is the effect of PTH on the bone?
Increased Calcium resorption from the bone
Why is the net effect on phosphate 0?
PTH = Excretion
Vitamin D = Reabsorption therefore overall effect is zero
What is the effect of FGF23?
Increases phosphate excretion