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MSK > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

Where is the main reservoir of calcium

A

Skeleton
1200g

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2
Q

Apart from the skeleton calcium can be stored in extra-cellular space why is this important

A

It is important for cells functions such as
Normal blood clotting
Muscle contractility
Nerve function

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3
Q

What is the total serum calcium

A

Around 2.4 mol/L

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4
Q

What is the total ionised serum calcium

A

Around 1.1 mol/L

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5
Q

If calcium is ionised what does this mean

A

Metabolically active

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6
Q

If calcium is protein bound what does this mean

A

It is not metabolically active

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7
Q

What are examples of complexed calcium

A

Citrate
Phosphate

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8
Q

When is albumin most likely going to bind to calcium

A

At higher pH

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9
Q

What is low iconised calcium associated with

A

It is associated with contraction of the small muscles of the hands and feet

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10
Q

Low ionised calcium can be an effect of what

A

Alkalosis

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11
Q

How much calcium do we absorb from our diet

A

30%

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12
Q

What is a major source of dietary calcium

A

Dairy products

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13
Q

What are minor sources of dietary calcium

A

Veg such as broccoli
Cereals such as white bread
Oily fish such as sardines

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14
Q

Where is active absorption of calcium happening

A

Active absorption occurs in the duodenum and jejunum

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15
Q

Where is passive absorption seen

A

Passive absorption occurs in the ileum and colon

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16
Q

When do we absorb a higher amount of calcium

A

When we are put on a low calcium diet

17
Q

What is calcium absorption mediated by

A

Calcritriol

18
Q

What is calcitriol

A

The active form of vitamin D

19
Q

How is calcium absorbed

A

Active transport

20
Q

Where is exchangeable calcium found

A

On the bone surface

21
Q

What happens during bone resorption

A

Calcium is released from bone slowly by osteoclasts

22
Q

What does the amount of calcium filtered by the glomerulus depend on

A

The glomerular filtration rate

23
Q

What is ultrafilterable calcium

A

Ionised and complexed

24
Q

How much of the calcium which is filtered is reabsorbed

A

98%

25
Q

Higher levels of calcium will be reabsorbed if what is high

A

Parathyroid hormone

26
Q

What causes less calcium to be reabsorbed

A

Sodium is high

27
Q

How many amino acids is parathyroid hormone

A

84 amino acids

28
Q

What can detect the levels of ionised calcium to stimulate PTH been secreted

A

Calcium sensing receptors on the parathyroid gland

29
Q

What regulates the synthesis of PTH

A

Calcitriol

30
Q

Where does regulation of PTH take place

A

Parathyroid chief cell

31
Q

What does calcitriol stimulate

A

It stimulates intestinal calcium absorption

32
Q

Where is calcitonin produced

A

It is produced by c cells or parafollicular cells of the thyroid

33
Q

When is calcitonin released

A

It is secreted due to an increase in serum calcium

34
Q

What affect does it have on resorption

A

Lowers bone resorption

35
Q

What does parathyroid hormones act on

A

Bone and kidney

36
Q

What does parathyroid hormone have an effect on

A

In the kidneys- increased calcium reabsorption, decreased phosphate reabsorption and increases alpha-hydroxylation of 25-OH vit D

In the bone- increased bone remodelling

In the intestines- no direct effect but increase in calcium absorption due to increase in 1,25 vit D

37
Q

What are bodily responses to a low diet of calcium

A

Low dietary calcium means less calcium is absorbed which results in lower ionised serum calcium cause high amounts of PTH which results in fast action in exchangeable calcium released from the surface of done and decreased excretion of calcium from the kidney
The slow actions = increased bone resorption and increase in fractional absorption by intestine
To return serum ionised calcium back to normal

38
Q

What is calcium homeostasis

A

Example of negative feedback

MSK (12 decks)

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