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Endocrine > Calcium > Flashcards

Calcium Flashcards

1
Q

What are the roles of calcium in the body

A 
Signalling 
Blood clotting 
Apoptosis 
Skeletal strength 
Membrane excitability
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2
Q

How does hypercalcaemia affect membrane excitability

A

o Hypercalcaemia decreases neuronal Na+ permeability which will reduce excitability and depress neuromuscular activity and in extreme cases, trigger cardiac arrhythmias.

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3
Q

How does hypocalcaemia affect membrane excitability

A

o Hypocalcaemia increases neuronal Na+ permeability leading to hyperexcitation of neurons. In extreme cases causes tetany, if spreads to larynx and respiratory muscles – asphyxiation.

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4
Q

How much total body calcium is stored in bones

A

99%

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5
Q

How much total body calcium is stored intracellularly

A

0.9% (mitochondria and sarcoplasmic reticulum)

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6
Q

How much total body calcium is stored extrecellularly

A

0.1%

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7
Q

How much of the extracellular calcium is bound to plasma proteins

A

40%ish

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8
Q

What proteins does calcium bind to

A

Globin 20%

Albumin 80%

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9
Q

What is normal plasma calcium range

A

2.2-2.6mM (0.1%) (not all of this is free)

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10
Q

What effect will high albumin have on plasma Ca levels

A

Decrease amount of free plasma calcium (as more is bound to albumin)

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11
Q

What condition features high plasma albumin

A

Multiple myeloma

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12
Q

What condition features low plasma albumin

A

Malnutrition

Nephropathy

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13
Q

What effect will low albumin have on plasma Ca levels

A

Low albumin levels increase free or available calcium.

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14
Q

What % of filtered calcium is reabsorbed in the kidney

A

97.99%

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15
Q

What affects the total amount of calcium in the plasma

A

pH

Bones

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16
Q

How does pH affect plasma calcium levels

A

Low pH increases free plasma calcium because the hydrogen ions compete with the Calcium ions for a spot on the plasma proteins

17
Q

How do bones affect plasma calcium levels

A

99% of total body Ca2+ is stored in bone and this can be added to or released as required and there is a continuous turnover of bone, it is continually being deposited and then resorbed.

18
Q

What bone cell is responsible for breaking down bone and reelaseing calcium

A

Osteoclast

19
Q

What bone cell is responsible for building bone from calcium and phosphate

A

Osteoblasts

20
Q

What is an osteocyte

A

A matured osteoblast that is less active

21
Q

How do osteoclasts mobilise bone

A

They secrete H+ ions (pH 4) to dissolve the calcium salts and also provide proteolytic enzymes to digest the extracellular matrix.

22
Q

What hormones are involved in calcium homeostasis

A

Parathyroid hormone
Calcitriol

Calcitonin

23
Q

What kind of hormone is PTH

A

polypeptide

24
Q

What kind of hormone is calcitriol

A

Steroid

25
Q

What kind of hormone is calcitonin

A

Peptide

26
Q

Where is calcitonin released from

A

The parafollicular (clear) cells of the thyroid gland

27
Q

Where are parathyroid glands located and how many are there

A

There are usually 4 lying on the posterior surface of the thyroid gland, although variations in number and location of are common, 1 in 10 people have aberrant distribution.

28
Q

How does parathyroid hormone affect Calcium levels (x5)

A

Stimulating osteoclasts to increase resorption (release) of Ca2+ and phosphate in bone

Inhibiting osteoblasts thus reducing Ca2+ deposition in bone.

Increasing reabsorption of Ca2+ from the kidney tubules, therefore decreasing its excretion in the urine.

Increasing renal excretion of phosphate. This elevates free [Ca2+ ] by preventing it from being deposited back into bone (into hydroxyappetite), a process that requires phosphate.

Stimulates the kidney to synthesise calcitriol from vitamin D which promotes calcium absorption at the gut and kidney.

29
Q

How long does it take for osteoclast stimulating effects of PTH to be seen after release

A

12-24hrs

30
Q

What is calcitriol

A

the active form of Vitamin D3

31
Q

What is calcitriols effect on calcium

A

It complements the actions of Parathyroid hormone and increases plasma calcium.

32
Q

How is calcitriol produced

A

From a two step process from inactive Vit D(cholecalciferol)

33
Q

Where does stage one of calcitriol formation occur

A

Liver

34
Q

Where does stage two of calcitriol formation occur

A

Kidneys

35
Q

What stage of calcitriol production is PTH needed

A

Stage 2 (in the kidneys)

36
Q

What hormones enhance the effect of calctriol

A

PTH

Prolactin

37
Q

How does calcitrol increase plasma calcium

A

Increase absorption of Ca2+ from the gut.

Facilitates renal absorption of Ca2+ and Phophate

Mobilises calcium stores in bone by stimulating osteoclast activity.

38
Q

If PTH increases phosphate excretion then why does calcitriol stimulate phosphate resabsorpion

A

To ensure any excess calcium to be laid down as bone.

39
Q

When does calcitriol Mobilises calcium stores in bone by stimulating osteoclast activity.

A

Only when calcium levels are low

Endocrine (14 decks)

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