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Endocrine > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

What does removal of calcium require

A

Active transport

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2
Q

What is the role of calcium in the body

A 
Signalling
Blood clotting 
Apoptosis
Skeletal strength
Membrane excitability
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3
Q

What is calcium’s role in signalling

A

Exocytosis of vesicles containing hormones
Contraction of muscles
Alters enzymes function

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4
Q

What does hypocalcaemia do to membrane excitability

A

Increases Na permeability
Leads to depolarisation
If extreme = tetany (sustained contraction)
Asphyxiation if resp muscles affected

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5
Q

What does hypercalcaemia do to membrane excitability

A

Decreased Na permeability
Reduces excitability
Can trigger arrhythmia

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6
Q

How is calcium distributed in the body

A 
Bone (99%) 
Intracellular fluid (0.9%)
Extracellular fluid (0.1%)
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7
Q

How is calcium stored in the bone and why is this important

A

Hydroxyapatite (Ca10(PO4)6OH2)

If phosphate deficient can’t lay down calcium in bone

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8
Q

How is calcium stored in extracellular fluid and why important

A

This is the value hypo / hyper relates too
Tightly regulated
1/2 bound to protein

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9
Q

What affected binding capacity

A

pH

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10
Q

What does alkalosis cause

A

H+ ions leave protein to fix alkalosis so are space for Ca to bind
Plasma conc of Ca fall = hypcalcaemia

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11
Q

What does acidosis cause

A

Increased H+ ions in plasma displaces bound Ca from protein = hypercalcaemia

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12
Q

What takes precedence over skeletal structure of bone

A

Calcium levels in ECF so if low Ca released from bone

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13
Q

What do osteoblasts do

A

Bone building cells

Lay down collagen

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14
Q

What do osteocytes do

A

Regulate bone metabolism

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15
Q

What do osteoclasts do

A

Calcium releasing cells

Secrete H+ ions to dissolve calcium salts and digest matrix

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16
Q

What are three key hormones involved in calcium homeostasis

A

PTH
Calcitriol
Calcitonin

17
Q

What produced PTH and when

A

Parathyroid hormones in response to low calcium

18
Q

How is calcitriol produced

A

Steroid hormone
Produced from diet vit D in liver and kidney
Inactive vit D goes to liver
Transported to kidney

19
Q

What stimulates calcitriol

A

PTH stimulates kidney to produce from vitamin D

Prolactin in lactating women as need Ca for milk

20
Q

What is full name of calcitriol

A

1,24 dihydroxycholecalciferol

21
Q

What is the role of PTH

A

Stimulate osteoclast to release Ca + phosphate
Inhibit osteoblasts
Increase reabsorption of Ca from kidney
Increase renal excretion of phosphate so can’t deposit in bone
Stimulates kidney to synthesise calcitriol from vitamin D
Overall effect is increased calcium and decreased phosphate

22
Q

What do you need in renal failure

A

Active vit D (calcitriol) as unable to make

23
Q

What does calcitriol do

A

Increases Ca uptake from small intestine
esp during pregnancy / lactation + growth
Increases renal absorption
Increases osteoclast activity

24
Q

Where do we get our vit D and where is it stored

A

Diet
Sunlight activates so clothing / sunscreen = deficient
Stored in fat

25
Q

Who is at risk of vitae’s D deficiency

A

Children
Elderly
Asian as pigmented skin less able to make

26
Q

What happens if deficient

A

Decreased plasma Ca which leads to increased PTH to increase
Calcium and phosphate removed from bone = osteoporosis

27
Q

What is vit D deficiency implicated in

A

MS
Cancer
Arthritis
CVD

28
Q

What is calcitonin and what does it do

A

Peptide hormone produced by thyroid
Acts to decrease plasma Ca
Stimulated by hypercalcaemia

29
Q

How does calcitonin work

A

Binds to osteoclast and inhibits release of Ca

Increases renal excretion of Ca

30
Q

What are other hormones involved in Ca homeostasis

A 
Cortisol = lose Ca 
Insulin = Ca in bone 
Oestrogen = Ca in bone 
GH = Ca in bone 
Prolactin
31
Q

What does cortisol do

A

Inhibits osteoblasts
Increases renal excretion of Ca and phosphate
Reduced absorption of Ca
Leads to decreases Ca and increased PTH

32
Q

What does this lead too

A

Osteoporosis

33
Q

What does insulin do

A

Increased bone formation as glucose used for energy
Antagonises cortisol
DM = bone loss

34
Q

What does oestrogen do

A

Simulates bone formation via osteoblasts
If post-menopausal = osteoporosis
Osteoporotic fracture rare if pre-menopausal women

35
Q

What does GH do

A

Stimulates bone formation

36
Q

What does prolactin do

A

Stimulates synthesis of calcitriol

Endocrine (17 decks)

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