Calcium homeostasis

Question 1

does an increase or a decrease in plasma PH cause hypocalcaemia and how?

Answer 1

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

Question 2

what effects does hyper and hypocalcaemia cause?

Answer 2

hypercalcaemia = arhythmias 
hypocalcaemia = tetany

Question 3

how does hypocalcaemia cause tetany?

Answer 3

hypocalcaemia increases neuronal Na permeability = hyperexcitation of neurones

Question 4

how does hypercalcaemia cause arrhythmias?

Answer 4

hypocalcaemia decreases Na permeability t= reduced excitability and depresses neuromuscular activity

Question 5

what effect does Ca have on membrane excitability?

Answer 5

Ca decreases Na permeability

Question 6

what hormones increase Ca?

Answer 6

parathyroid hormone

calcitriol

Question 7

what hormone decreases Ca?

Answer 7

calcitonin

Question 8

what levels do vitamin D fall to when you are deficient?

Answer 8

<20 ng/ml

Question 9

does PTH increase or decrease the excretion of phosphate in the urine and why?

Answer 9

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

Question 10

what is the action of calcitriol?

Answer 10

it compliments the actions of PTH by increasing Ca

Question 11

what is calcitriol produced by?

Answer 11

dietary vitamin D
precursors activated by uv rays on skin
formation also stimulated by prolactin in lactating women

Question 12

what is calcitriol?

Answer 12

inactive form of vitamin D
steroid hormone
works to increase Ca levels
produced from the parathyroid gland

Question 13

how does calcitriol increase Ca?

Answer 13

increases Ca reabsorption from the gut
fascillitates renal absorption of Ca
mobilises Ca stores in bone by stimulating osteoclast activity

Question 14

what can vitamin D deficiency lead to in children and adults?

Answer 14

children = rickets
adults = osteomalacia

Question 15

what conditions is vitamin D involved with?

Answer 15

MS
arthritis
CVD
cancers

Question 16

how does calcitonin decrease calcium?

Answer 16

binds to osteoclasts and inhibits bone resorbtion

increases renal excretion of Ca

Question 17

apart from PTH, calcitriol and calcitonin, what other hormones regulate Ca balance?

Answer 17

insulin (diabetics may have bone loss) 
prolactin
growth hormone (bone formation)
oestrogen (bone formation) 
cortisol (decreases Ca, increases PTH and increases bone resorption)

Question 18

how does prolactin alter Ca balance?

Answer 18

prolactin promotes Ca absorption from the gut by stimulating the synthesis of calcitriol
this is because its important to increase Ca in lactating women

Question 19

how is inactive vitamin D synthesised to form calcitriol?

Answer 19

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

Question 20

what is the volume of Ca in the plasma?

and what volume in the plasma is physiologically active?

Answer 20

2. 2-2.6mM in plasma

1. 2mM is active

Question 21

what is the role of Ca in the body?

Answer 21

signalling
membrane excitation
blood clotting
apoptosis
skeletal strength

Question 22

how can a low plasma Ca cause phosphate deficiency?

Answer 22

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

Question 23

how can cortisol cause osteoporosis?

Answer 23

cortisol causes a decrease in plasma Ca
decrease in Ca = increase in PTH
PTH increases bone resorption = osteoporosis (over time)

Question 24

how does PTH increase Ca?

Answer 24

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