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MSK > Calcium > Flashcards

Calcium Flashcards

1
Q

What is the daily calcium intake

A

500 - 1500 mg/day

About 30% of dietary calcium is absorbed

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2
Q

Where is calcium stored

A

99% of total calcium is stored in the skeleton

Remainder distributed between intracellular and extracellular fluid

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3
Q

What is calcium required for

A

Physiological processes
- skeletal growth and maintenance
- Normal blood clotting
- Muscle contractility
- Nerve function

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4
Q

What is the plasma concentration off calcium

A

Controlled to narrow limits

2.2-2.6 mmol/L

approx. 45% bound to plasma proteins - biologically unavailable

45% circulating ionised form

10% bound to other proteins
- citrate
- phosphate

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5
Q

What % of plasma calcium is bound to plasma proteins

A

45%

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6
Q

What % of plasma calcium is circulating in its ionised form

A

45%

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7
Q

What % of plasma calcium is bound to compounds such as citrate and phosphate

A

10%

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8
Q

When is calcium metabolically active

A

In ionised state

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9
Q

What organ regulates the amount of calcium excreted in the body

A

Kidney

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10
Q

Approximately what % of serum calcium filtered by the kidneys is reabsorbed

A

98%

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11
Q

Where is calcium reabsorbed in the kidneys

A

Passively - proximal tubule and ascending loop of Henle

Actively - Distal tubes of the kidneys

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12
Q

What happens when plasma calcium falls

A

Bone mineral reservoir acts by increasing the rate of bone resorption

Leads to a decrease in bone mineral density

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13
Q

What acts as a readily accessible source of exchangeable calcium

A

Skeleton

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14
Q

What are the most important hormones in calcium homeostasis

A

PTH

Calcitriol (1,25 dihydroxy Vitamin D)

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15
Q

What is the role of PTH in calcium homeostasis

A

Release is increased in response to low serum ionised calcium

Parathyroid gland senses changes through calcium sensing receptors

Acts in three ways to increase serum calcium
1. Decreasing renal calcium excretion
2. Increasing bone reabsorption
3. Enhancing dietary calcium absorption by stimulating the production of calcitriol in the kidney

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16
Q

What is the role of calcitonin in calcium homeostasis

A

Secreted by cells in the thyroid glands

Reduces serum calcium concentration

17
Q

How much calcium is in the skeleton

A

1200g

18
Q

How much calcium is in extracellular space

A

1g

19
Q

How much in mmol/L is the ionised serum calcium

A

1.1. mmol/L

20
Q

What is the affect of alkalosis on calcium

A

Higher pH albumin binds strongly to calcium

Total serum calcium = unchanged (2.4 mmol/L)
Ionised serum calcium = decrease (0.9mmol/L)

Extracellular fluid space calcium is in equilibrium with ionised calcium

21
Q

What is low ionised calcium associated with

A

Contraction of the small muscles of the feet and hands = tetany

Due to depolarisation of the long nerves of the upper limb

22
Q

What are the three ways homeostasis is maintained

A

Calcium absorption (from intestines) / endogenous faecal Ca

Calcium reabsorption (from kidneys) / Ca excretion

Bone resorption / bone formation

23
Q

What are the source of dietary calcium

A

Major source = dairy products 2/3

Minor sources
- vegetables e.g. broccoli
- cereals e.g. white bread
- oily fish e.g. sardines

24
Q

What % of dietary calcium do we absorb

A

30%

25
Q

When do we absorb a higher fraction of calcium

A

When put on a low calcium diet

Mediated by calcitriol - the active form of vitamin D

Most calcium is absorbed by active transport

26
Q

When can calcium be released rapidly

A

Exchangeable calcium on the bone surface

27
Q

When can calcium be released slowly

A

By osteoclasts during bone resorption

28
Q

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

A

Glomerular filtration rate

Ultra filterable calcium
- ionised
- complexed

29
Q

What increases/decrease the amount of calcium reabsorbed

A

More - PTH level is high

Less - filtered sodium is high
High sodium diet decreases Claudin-2 expression, resulting in increased TRPV5 and calcium transport

30
Q

Describe calcitonin

A

Hormone produced by C cells (parafollicular cells) in thyroid

Secretion is stimulated by an increase in serum calcium

Effect is to lower bone resorption

Importance in man is uncertain

31
Q

What is the action of the parathyroid hormone

A

Acts on
- bone
- kidney

Uses second messengers such as cyclic AMP, calcium

Positive and negative signs relate to actions in osteoblasts

32
Q

What is the response to a low calcium diet

A

Low dietary calcium =
Less calcium is absorbed =
Results in low serum ionised calcium =
Results in higher PTH =
Results in fast and slow responses

Returns serum ionised calcium to normal

33
Q

What is low dietary calcium an example of

A

Negative feedback

MSK (13 decks)

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