regulation of calcium Flashcards
(25 cards)
types of extracellualr/plasma calcium
- ionised and unbound (50%) -> body will sense this one
- calcium complexed with anions (5%)
- protein bound (45%) -> metabolism
how much calcium is in the bones
99%
phosphate distribution throughout body
- extracellular matrix -> 85% in bone as hydrosyapetite
- extracellular fluid -> inorganic phosphates
- intracellular = organic
magnesium distribution in body
- majority in bone
- <1% present in EF/plasma
- used in metabolism, neuromuscular excitability , enzyme, DNA etc
how can calcium be added to plasma (added to body)
- absorption from digesive tract
- resorption of bone (mobilise)
- reabsorption from kidney (after filtration) -> fine tuning
how is calcium removed from plasma?
- calcification of bone
- filtration in kidneys
what does vitamin D do for calcium
- activates cholecalciferol in liver to dihydroxycholecalciferol
/calcitriol in kidney (D3)-> reegulates Ca uptake and mineralisation
where are calcium sensing recpetors found
- parathyroid, thyroid gland, kidney, bone, GIT and other tissues
- important in kindey and parathyroid
what secretes parathyroid hormone
- chief cells in parathyroid gland
how does the parathyroid gland release PTH
- sensors for level of plasma calcium ionisation
- responds more drastically to hypocalcaemia
explain the mechanisms for hypocalceamia
- parathyroids detect low ionised calcium -> secrete PTH to kidney -> turns vit D into calcitriol
- calcitriol acts on bone to resorb (mobilise), intestine to absorb more, and kidney to reabsorb more (distal)
effect of PTH on kidney
- stimulate Ca2+ reabsroption in distal nephron
- inhibits phosphate reabsroption -> proximal and distal to maintain ratio of Ca:P -> more P excreted in urine
- stimulates calcitriol from vit D (increase 1 alpha hydroxylase activity)
what does PTH do to bone
- increase synthesis of RANKL -> increases osteoclast activation -> breakdown into calcium and phosphorus
steps of vit D to calcitriol
- inactive vit D from diet or sunlight (skin)
- unregulated conversion to 25(OH)D3 in liver
- regulated conversion to calcitriol in kindey (by 1 alpha hydroxylase)
- PTH required for activation at kidney
what does calcitriol do in gut, bone and kindey
- increases calcium and P uptake in GIT
- increase oseteclastic activity
- increase calcium reabsorption n distal tubule
what does calcitriol do to parathyroid gland
- neg feedback to decrease PTH transcription
difference between PTH and calcitirol effects
- in kidney PTH causes P excretion but calcitriol causes uptake/reabsorption
- PTH effects bones and kidney, but not gut. calcitrol does all 3
levels of magnesium and phosphorus required during hypocalceamia to stimulate PTH
- high magnesium
- high phosphate
what does calcitonin do?
- during hypercalcaemia, released from C-cells of thyroid
- decreases reabsorption of Ca and P in kindeys (more out)
- decreases oseocytes to decrease bone resorption
- negative feedback system with ionised Ca2+
what are the common displays of hypocalcaemia
- high PTH and calcitriol
- increased bone resorption (thinning of bone)
- increased intestinal absorption of Ca
- decreased fractional excretion of Ca (kidney) -> reabsorb way more than excreted
- increased fractional excretion of P (kidney) -> not reabsorbing calcium
what is milk fever
- dairy cow
- cow can’t get up because it doesn’t have enough calcium
- due to extremely high requirements of calf development + colostrum requirments
- imparied Ca absorption and slow mobilisation
- also delayed or insufficient calcitriol
stages of milk fever
- agitation, muscle tremors
- stagger and lie down/sitting position
- lie flat on side
- circulatory collapse, coma and death
what is hypocalcceamia tetany (eclampsia)?
- small dog has large litter -> tetany
- prolonged stage 1 (convulsions)
what does renal failure do to calcium
- hypocalceamia
- inability to syntehsise calcitriol
