Calcium Homeostasis

Question 1

how is the blood clotting ability of calcium utilised clinically

Answer 1

anti calcium agents are used to line the sample tube to prevent blood samples from clotting

Question 2

where is 99% of the body’s calcium

Answer 2

in bone as hydroxyapatite

Question 3

what percentage of calcium in the body is free and physiologically active

Answer 3

0.05%

Question 4

purpose of calcium in cell signalling

Answer 4

their entry and exit into the cell triggers release of hormones (as in B cells for insulin) or neurotransmitters

Question 5

5 roles of calcium

Answer 5

1. signalling
2. blood clotting
3. apoptosis
4. skeletal strength
5. membrane excitability

Question 6

how does calcium produce membrane excitation

Answer 6

RCMP is produced by Na+/K+ movement. Calcium decreases Na+ permeability and reduces excitability

Question 7

which of the mentioned 5 roles of calcium is most critical to maintain homeostasis of an why

Answer 7

membrane excitability: if nerves/cells become hyperactive or underactive then chaos

Question 8

what state of calcium (hyper/hypo) will cause Na+ permeability in neurons to increase (i.e. hyperexcitation) and what is the clinical consequence

Answer 8

HYPOcalcaemia. results in tetany. If this tetany spreads to the chest wall muscles and larynx it can results in asphyxiation

Question 9

cardiac arrhythmia can be triggered by what state of calcium (hyper/hypo)

Answer 9

HYPERcalcaemia. decreased neuronal Na+ permeability –> reduced excitability –> depressed neuromuscular activity

Question 10

what % of body calcium is stored intracellularly for things like muscle contraction

Answer 10

0.9%

Question 11

normal calcium range in plasma (i.e. ECF)

Answer 11

2.2-2.6mM

Question 12

How is the 0.1% calcium in plasma distributed

Answer 12

10% complexed to anion, 40% protein bound, 50% free

Question 13

how does alkalosis increase the amount of calcium bound to proteins

Answer 13

fewer H+ ions –> fewer H+ to bind to proteins –> more spaces on proteins to bind to –> Ca2+ binds to spaces on protein

Question 14

which situation has more protein bound calcium, alkalosis or acidosis

Answer 14

alkalosis

Question 15

true/false calcium in bone will be released if Ca2+ levels in plasma are not sufficient

Answer 15

true - osteoclasts secrete H+ to dissolve the hydroxyapatite

Question 16

what cells build up bone

Answer 16

osteoBlasts. they lay down a collagen matrix which is then calcified. It is this matrix that calcium is taken from

Question 17

the two key hormones of raising calcium content in blood

Answer 17

parathyroid hormone and calcitrol

Question 18

what vitamin is calcitrol derived from

Answer 18

vitamin D3

Question 19

3 main sites of PTH action

Answer 19

bones, renal tubules and kidneys themselves

Question 20

Ca2+ raising action of PTH on bone

Answer 20

stimulating osteoclasts
inhibiting osteoblasts
i.e. more breakdown, less deposition

Question 21

action of PTH to raise Ca2+ in kidneys

Answer 21

increase renal excretion of phosphate, so it can’t join back up with calcium to form hydroxyapatite.

stimulate kidneys to make calcitriol from vit D

Question 22

how does PTH raise Ca2+ by acting on the renal tubules

Answer 22

by increasing reabsorption of Ca2+ i.e. not be peed out

Question 23

calcitriol formation is stimulated by what hormone in lactating women

Answer 23

prolactin

Question 24

how does calcitriol increase gut Ca2+ absorption

Answer 24

by increasing expression for calcium transporters in gut

Question 25

2 stimuli of calcitriol formation

Answer 25

prolactin and PTH

Question 26

where do we acquire vitamin D from

Answer 26

from diet and from cholesterol precursors activated by UV light

Question 27

vitamin D is fat/water soluble?

Answer 27

fat soluble

Question 28

what hormones decreases plasma Ca2+

Answer 28

calcitonin

Question 29

3 calcium raising action of calcitriol

Answer 29

1. increased absorption in gut 2. renal absorption 3. stimulating osteoclasts

Question 30

why might prolactin increase Ca2+

Answer 30

because lactating women have an increased demand for calcium as they are producing milk

Question 31

effect of reduced vitamin D on bones

Answer 31

less calcitriol produced --> less Ca2+ from gut and kidneys --> PTH works harder --> more phosphate excreted --> greater Ca2+ loss from bone --> weaker, softer bones --> rickets/osteomalacia

Question 32

where is calcitonin secreted from

Answer 32

the thyroid gland

Question 33

what stimulates calcitonin release

Answer 33

raised blood calcium

Question 34

2 calcium lowering actions of calcitonin

Answer 34

1. inhibit osteoclasts | 2. increase renal excretion of Ca2+

Question 35

true/false excess calcitonin causes hypocalcaemia

Answer 35

false - its effects are overridden by PTH being stimulated by the low calcium levels produced

Question 36

what hormone might be useful to treat Paget's disease (overactive osteoclasts)

Answer 36

calcitonin --> it inhibits osteoclasts