calcium homeostasis

Question 1

five functions of Ca2+ in the body?

Answer 1

signalling 
blood clotting 
apoptosis
skeletal strength 
membrane excitability

Question 2

signalling function of Ca2+?

Answer 2

exocytosis of synaptic vesicles.- e.g. insulin

Question 3

what is the result of defective apoptosis function?

Answer 3

cancers/tumour growth

Question 4

membrane excitability function of Ca2+?

Answer 4

decreases Na+ permeability

Question 5

which Ca2+ function is most important short term?

Answer 5

membrane excitability is most critical in short term homeostasis

Question 6

effects of hypocalcaemia?

Answer 6

increases neuronal Na+ permeability

• > hyperexcitation of neutrons
• > tetany & asphyxiation

Question 7

effects of hypercalcaemia?

Answer 7

decreases neuronal Na+ permeability

• > reduced excitability
• > cardiac arrhythmia

Question 8

where is the Ca2+ in the body?

Answer 8

bones - 99%
intracellular - 0.9%
ECF - 0.1%

Question 9

how much Ca2+ in the body is free in solutions and therefore physiologically active?

Answer 9

0.05%

Question 10

how much does Ca2+ weigh in the extracellular matrix of the bone?

Answer 10

~1kg

Question 11

where is Ca2+ stored in the bone?

Answer 11

extracellular matrix, in the form of hydroxyapatite

Question 12

what’s important in maintaining the homeostasis of Ca2+?

Answer 12

phosphate homeostasis

Question 13

describe the difference between free ionised Ca2+ in plasma and overall plasma Ca2+ content?

Answer 13

overall - ~2.4mM
free ionised - ~1.2mM
i.e. 50%

Question 14

% of Ca2+ in plasma bound to proteins?

Answer 14

40%

Question 15

% plasma Ca2+ bound to plasma anions? i.e. complexed

Answer 15

10% - these are the left over Ca2+ molecules

Question 16

which Ca2+ ions are deemed physiologically active?

Answer 16

the free Ca2+ ions (50%)

Question 17

name 2 proteins Ca2+ could bind to in plasma and at what ratio?

Answer 17

albumin (80%)

globulin (20%)

Question 18

what is the effect of increasing alkalotic conditions?

Answer 18

increased binding capacity of plasma proteins

Question 19

effect of hyperventilating on Ca2+ binding?

Answer 19

plasma pH rises

• > more alkalotic
• > plasma proteins bind MORE to Ca2+
• > plasma conc. falls
• > hypocalcaemic tetany

Question 20

calculation: total body Ca2+?

Answer 20

Ca2+ in - Ca2+ out

Question 21

which substance is needed to maintain the renewal of bone?

Answer 21

phosphates

Question 22

what do osteoBlasts do?

Answer 22

highly active bone-Building cells which lay down collagen extracellular matrix which they calcify

Question 23

how are osteocytes formed?

Answer 23

osteoblasts differentiate in established bone to produce ostecytes

Question 24

function of osteoClasts?

Answer 24

cells that mobilise the bone by secreting H+ ions which dissolve Ca2+ salts

Also produce proteolytic enzymes to digest extracellular matrix

Question 25

which 2 hormones increase Ca2+ plasma conc?

Answer 25

PTH

Calcitriol

Question 26

how is calcitriol produced?

Answer 26

the active form of vit. D3 which is produced by liver and kidneys

Question 27

location and number of parathyroid glands?

Answer 27

posterior surface of thyroid gland

usually 4

Question 28

common reason for abnormal location/less parathyroid glands?

Answer 28

ectopic glands or most commonly….

SURGERY - thyroidectomy

Question 29

when is PTH released?

Answer 29

response to decreases in free Ca2+ plasma conc.

Question 30

name 5 ways that PTH acts to increase free Ca2+ conc in plasma?

Answer 30

1 - stimulate osteoclasts

2 - inhibits osteoblasts

3 - increases reabsorption of Ca2+ from kidney tubules

4 - increases renal excretion of phosphate

5 - stimulates synthesis of calcitriol

Question 31

where does vitamin D come from in order to produce calctiriol?

Answer 31

sun - precursors

dietary

Question 32

which hormone (women) also stimulates calcitriol formation?

Answer 32

prolactin

Question 33

target tissues of calcitriol?

Answer 33

intestine
bone
kidney

Question 34

3 actions of calcitriol?

Answer 34

1 - increase absorption of Ca2+ from gut

2 - facilitates renal absorption of Ca2+

3 - mobilises Ca2+ stores in bone

Question 35

collectively, how is plasma Ca2+ conc. increased?

Answer 35

secretion of PTH and calcitriol

Question 36

who has a high circulating level of 1,25(OH)2D and what is the effect on amount of dietary Ca2+ absorbed?

Answer 36

those affected by growth spurts, pregnancy, lactation

increases Ca2+ absorbed (45-55%)

Question 37

who has a low circulating level of 1,25(OH)2D and what is the effect on amount of dietary Ca2+ absorbed?

Answer 37

those who are vit. D deficient

decreases Ca2+ absorbed (10-15%)

Question 38

how much % of dietary Ca2+ is absorbed in a healthy individual?

Answer 38

30%

Question 39

define vit. D deficiency?

Answer 39

Circulating vitamin D levels are less than 20ng/ml

Question 40

risks of vit. D defiance in adults v.s. children?

Answer 40

children - rickets

adults - osteomalacia

Question 41

4 diseases in which vit. D deficiency is implicated?

Answer 41

MS
cancer
arthritis
CVD

Question 42

which is the ONLY hormone to decrease Ca2+ levels in plasma? where is it produced?

Answer 42

Calcitonin - thyroid gland

Question 43

result of excess calcitonin?

Answer 43

nothing - overridden by PTH

Question 44

when can calcitonin be used as a treatment?

Answer 44

Paget’s disease - where osteoclasts are overactive