Calcium Homeostasis Flashcards
what is the calcium sensing receptor?
GPCR
where is the calcium sensing receptor?
on the parathyroids
when is PTH stimulated?
hypocalcaemia
what does PTH act on?
bone
kidneys
intestines
what does PTH cause in bone?
increases osteoclasts
reduces osteoblasts
more calcium is excreted into the bloodstream
what does PTH cause in the kidneys?
reabsorption of Ca2+ and excretion of phosphate
activation of vitamin D
what does PTH cause in the intestines?
reabsorption of Ca2+ from diet aided by vitamin D from the kidney (calcitriol)
causes of low vitamin D
poor intake malabsorption (disease) liver failure kidney failure sunscreen anticonvulsants
when is calcitonin secreted?
severe hypercalcaemia
what secretes calcitonin?
parafollicular C cells
action of calcitonin
reduces serum Ca2+
how does calcitonin reduce Ca2+
reduces tubular reabsorption
moves Ca2+ from plasma to bone
reduces bone resorption
two sources of vitamin D
diet UV light (dehydrocholesterol)
pathway to active vitamin D
cholecalciferol > liver enzyme
25 OH cholecalciferol > kidney enzyme
1,25 di-OH cholecaliferol
what activates the kidney enzyme in activation of vitamin D?
high PTH
low phosphate
