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Endocrine > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

what is the role of calcium In the body?

A 
> signalling
> blood clotting
> skeletal strength
> membrane excitability
> apoptosis
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2
Q

what is the effect of calcium on the permeability of membrane to sodium?

A

calcium decreases permeability

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3
Q

what is the effect of hypocalcaemia on the membrane excitability of neurons?

A

there is hyper-excitation (which can cause tetany)

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4
Q

how can hypercalcaemia cause cardiac arrhythmias?

A

there is a decrease in neuronal sodium permeability which reduces the excitability and depresses neuromuscular activity.

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5
Q

where is the intracellular calcium stored?

A

in mitochondria and sarcoplasmic reticulum

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6
Q

describe the calcium distribution in the body

A

> 99% is in bones
0.9% is in intracellular fluid
0.1% is in extracellular fluid

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7
Q

what percentage of calcium is bound to proteins?

A

40%

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8
Q

what is the normal extracellular calcium concentration in adults?

A

2.5mM

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9
Q

how much of the calcium is physically active (free ionised)?

A

1.2mM = 50%

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10
Q

if 50% ca is free ionised, 40% is protein bound where is the remaining 10% of extracellular calcium?

A

bound to plasma anions

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11
Q

true or false:

the binding capacity of calcium increases in alkalotic conditions

A

true

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12
Q

in hypoventilation how is the calcium concentration affected?

A

the plasma calcium decreases as the ph increases causing more calcium to bind to the plasma proteins

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13
Q

what is the function of osteoblasts?

A

they lay down collagen extracellular matrix and calcify it

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14
Q

what is the function of the osteoclasts?

A

they mobilise bone:
> secrete H ions (ph4) to dissolve calcium salts
> they provide proteolytic enzymes to digest extracellular matrix

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15
Q

what is the function of the osteocytes?

A

they regulate the activity of osteoblasts and osteoclasts

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16
Q

what do osteocytes differentiate from?

A

osteoblasts

17
Q

what 2 hormones increase calcium conc. in the plasma?

A

> parathyroid hormone

> calcitriol

18
Q

what produces calcitriol?

A

the liver and kidneys

19
Q

true or false:

calcitriol is an active form of vitamin D3

A

true

20
Q

what are the actions of the parathyroid hormone?

A

> stimulates osteoblasts
stimulates kidney to synthesise calcitriol
inhibits osteoblasts
increases calcium reabsorption from the kidney tubules
increases renal excretion of phosphate

21
Q

how does the increased excretion of phosphate elevate free calcium?

A

it prevents it from being deposited back into the bone

22
Q

what activates the formation of calcitriol?

A

prolactin

23
Q

what are the actions of calcitriol?

A

> increased calcium absorption from the gut
mobilisation of calcium stores in the bone
facilitation of renal absorption of calcium (osteoclasts)

24
Q

what is the effect of vitamin d deficiency?

A

since there is a decrease in calcium concentration in the plasma then to compensate calcium is removed from the bone causing osteomalacia and rickets

25
Q

what conditions does vitamin d deficiency have implications in?

A

> MS
cancer
arthritis
CVD

26
Q

what hormone decreases calcium conc.?

A

calcitonin

27
Q

what gland produces calcitonin?

A

thyroid gland

28
Q

true or false calcitonin is a steroid hormone?

A

false it is a peptide hormone

29
Q

what are the actions of calcitonin?

A

> inhibits bone resorption by binding to osteoclasts

> increased calcium excretion

30
Q

why does growth hormone affect calcium levels?

A

it is a constant stimulus for bone formation

31
Q

what is the effect of cortisol on calcium balance?

A

> increases renal excretion
inhibits osteoblasts
reduces intestinal absorption of calcium
decreases calcium plasma = increased parathyroid hormone

32
Q

what is the effect of insulin on calcium balance?

A

> increases bone formation

> antagonises cortisol

33
Q

why is osteoporosis a major problem in menopause?

A

oestrogen has a role in promoting bone formation

Endocrine (15 decks)

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