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MSK > Calcium Homeostasis > Flashcards

Calcium Homeostasis Flashcards

1
Q

Calcitonin is produced in ‘C-cells’ and is involved in calcium homeostasis. In which of the following are ‘C-cells’ located?

A

Thyroid gland

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2
Q

There are three major hormones involved in calcium regulation. Which of the following hormones is produced in response to an elevated serum calcium concentration?

A

Calcitonin

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3
Q

What is the main reservoir of calcium in the body

A

Skeleton

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4
Q

Amount of calcium in skeleton

A

1200g

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5
Q

Amount of calcium in extracellular space

A

1g

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6
Q

Function of calcium in extracellular space

A

Muscle contractility
Nerve function
Normal blood clotting

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7
Q

How is calcium in circulation

A

Ionised
Protein-bound
Complexed

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8
Q

Total serum calcium

A

2.4 mmol/L

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9
Q

Ionised serum calcium

A

1.1 mmol/L

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10
Q

Ionised calcium

A

Metabolically active

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11
Q

Protein bound calcium

A

Not metabolically active

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12
Q

What is calcium complexed with

A

Citrate
Phosphate

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13
Q

Modulation of ionised calcium by pH
Alkalosis

A

Higher pH- albumin more negatively charged to albumin strongly binds to calcium

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14
Q

Total serum calcium at alkalosis

A

Total serum calcium unchanged

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15
Q

Ionised serum calcium at alkalosis

A

Decreased

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16
Q

What is low ionised calcium associated with

A

Contraction of the small muscles of the hands and feet
- tetany
There is depolarisation of the long nerves of the upper limb

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17
Q

Major sources of dietary calcium

A

Dairy products
-2/3

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18
Q

Minor sources of dietary calcium

A

Vegetables eg broccoli
Cereals eg white bread
Oily fish eg sardines

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19
Q

Recommended intake of calcium

A

700 mg/day

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20
Q

What percentage of dietary calcium do we absorb

A

30%

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21
Q

Where does active absorption of calcium occur

A

Duodenum
Jejunum

22
Q

Where does passive absorption of calcium occur

A

Ileum
Colon

23
Q

When there is low availability of calcium , higher fractional excretion by

A

More active transport
Mediated by calcitriol (active form of vitamin D)

24
Q

What is the active form of vitamin D

A

Calcitriol

25
Q

Release of calcium from bone

A

Can be released rapidly from exchangeable calcium on the bone surface
Can be released more slowly by osteoclasts during bone resorption

26
Q

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

A

Glomerular filtration rate
Ultrafiltrable calcium (ionised and complexed)

27
Q

What percentage of filtered calcium in the kidney is reabsorbed

A

98%

28
Q

What is reabsorption of calcium in the kidney increased by

A

Parathyroid hormone

29
Q

What is the reabsorption of calcium in the kidney decreased by

A

If filtered sodium is high

30
Q

Fractional excretion of calcium from the kidney

A

2%

31
Q

Relationship between serum calcium and parathyroid hormone

A

Small changes in serum ionised calcium causes a big change in parathyroid hormone

32
Q

Parathyroid hormone actions

A

Increases Ca2+ reabsorption
Increases 1 alpha-hydroxylation of 25-OH vit D
Increases bone remodelling (resorption>formation)
Increases Ca2+ absorption due to increased 1,25 (OH)2 vit D

33
Q

Where is calcitonin produced

A

Thyroid C cells

34
Q

What causes the secretion of calcitonin

A

Increased serum calcium

35
Q

Effect of calcitonin

A

Lower bone resorption

36
Q

Calcitriol structure

A

Hydroxylated at positions 1 and 25

37
Q

Function of calcitriol

A

Stimulates intestinal calcium absorption

38
Q

Passive absorption of calcium in kidney

A

65% in PCT
25% in loop of henle

39
Q

Active absorption of calcium in kidney

A

8% in DCT

40
Q

Calcium sensing receptor on parathyroid gland

A

Gq coupled receptor

41
Q

Response to a low calcium diet

A

Lower serum calcium
Increased parathyroid hormone secretion

-exchangeable calcium released from surface of bone
-decreased excretion of calcium from kidney

42
Q

Vitamin D overdose

A

Increased gut absorption of calcium
Higher serum calcium
Decreased PTH
-decrease renal absorption of calcium
-Decreased bone resorption

43
Q

Substrate for vitamin D

A

Cholesterol

44
Q

Primary production of vitamin D in skin

A

UV light on 7-dehydroxycholesterol

45
Q

Where does primary production of vitamin D occur

A

Skin

46
Q

Where is vitamin D activated

A

Kidney

47
Q

Where is vitamin d first hydroxylated

A

Liver
- forms 25 -OHase

48
Q

Main function of calcitriol

A

Active gut absorption of dietary calcium

49
Q

Vitamin D synthesis

A

Can be ingested or synthesised from a cholesterol precursor: 7-dehydrocholesterol is converted into vitamin-D3 under the influence of UV radiation in the skin. In the liver, vitamin D3 is converted into 25-hydroxyvitamin D by 25-hydroxylase. In the kidney, 1-alpha-hydroxylase converts it into 1,25-dihydroxyvitamin D (calcitriol)

50
Q

Calcitriol mechanism

A

stimulates intestinal epithelial cells to increase synthesis of calbindin-D proteins which facilitate the transport of calcium from the intestinal brush border to the basolateral membrane for absorption into the blood.

MSK (11 decks)

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