Calcium homeostasis Flashcards
does an increase or a decrease in plasma PH cause hypocalcaemia and how?
when plasma PH decreases there is an increase in H ion
H ions displace Ca bound to proteins therefore increase free Ca in the plasma = hypercalcaemia
what effects does hyper and hypocalcaemia cause?
hypercalcaemia = arhythmias hypocalcaemia = tetany
how does hypocalcaemia cause tetany?
hypocalcaemia increases neuronal Na permeability = hyperexcitation of neurones
how does hypercalcaemia cause arrhythmias?
hypocalcaemia decreases Na permeability t= reduced excitability and depresses neuromuscular activity
what effect does Ca have on membrane excitability?
Ca decreases Na permeability
what hormones increase Ca?
parathyroid hormone
calcitriol
what hormone decreases Ca?
calcitonin
what levels do vitamin D fall to when you are deficient?
<20 ng/ml
does PTH increase or decrease the excretion of phosphate in the urine and why?
PTH increases the excretion of phosphate because phosphate is involved in the deposition of Ca in bone
therefore by reducing phosphate levels, it will reduce the amount of Ca deposited in bone = increasing plasma Ca
what is the action of calcitriol?
it compliments the actions of PTH by increasing Ca
what is calcitriol produced by?
dietary vitamin D
precursors activated by uv rays on skin
formation also stimulated by prolactin in lactating women
what is calcitriol?
inactive form of vitamin D
steroid hormone
works to increase Ca levels
produced from the parathyroid gland
how does calcitriol increase Ca?
increases Ca reabsorption from the gut
fascillitates renal absorption of Ca
mobilises Ca stores in bone by stimulating osteoclast activity
what can vitamin D deficiency lead to in children and adults?
children = rickets adults = osteomalacia
what conditions is vitamin D involved with?
MS
arthritis
CVD
cancers
how does calcitonin decrease calcium?
binds to osteoclasts and inhibits bone resorbtion
increases renal excretion of Ca
apart from PTH, calcitriol and calcitonin, what other hormones regulate Ca balance?
insulin (diabetics may have bone loss) prolactin growth hormone (bone formation) oestrogen (bone formation) cortisol (decreases Ca, increases PTH and increases bone resorption)
how does prolactin alter Ca balance?
prolactin promotes Ca absorption from the gut by stimulating the synthesis of calcitriol
this is because its important to increase Ca in lactating women
how is inactive vitamin D synthesised to form calcitriol?
calcitriol is active vitamin D
inactive vitamin D is fist synthesised in the liver to form 25 hydroxycholecalciferol which is then synthesised in the kidney to produce calcitriol
what is the volume of Ca in the plasma?
and what volume in the plasma is physiologically active?
- 2-2.6mM in plasma
1. 2mM is active
what is the role of Ca in the body?
signalling membrane excitation blood clotting apoptosis skeletal strength
how can a low plasma Ca cause phosphate deficiency?
PTH is released in response to low plasma Ca
PTH increases phosphate excretion from the kidneys to decrease Ca deposition in bone
therefor too much PTH = phosphate deficiency
how can cortisol cause osteoporosis?
cortisol causes a decrease in plasma Ca
decrease in Ca = increase in PTH
PTH increases bone resorption = osteoporosis (over time)
how does PTH increase Ca?
inhibits osteoblast activity therefore reducing deposition in bone
activates osteoclast activity to increase ca resorption from bone
increases Ca reabsorption from the kidneys
increasing renal excretion of phosphate
stimulating he production of calcitriol from vitamin D
