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Z OLD ESA 1- Metabolism > Calcium Metabolism > Flashcards

Calcium Metabolism Flashcards

1
Q

What regulate calcium balance?

A

Gut, Kidneys, Bone

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2
Q

What is the importance of calcium?

A

In plays a critical role in many cellular processes

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3
Q

Give 6 roles of calcium

A
  • Hormone secretion
  • Muscle contraction
  • Nerve conduction
  • Exocytosis
  • Activation of many enzymes
  • Intracellular second messenger
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4
Q

How does Ca 2+ serve as an intracellular second messenger?

A

By carrying information from the cell membrane to the interior of the cel

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5
Q

What is it important that the body regulates very tightly?

A

The plasma concentration of free ionised calcium ([Ca 2+ ])

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6
Q

Why is free ionised calcium concentration controlled?

A

Because this is the physiologically active form of the metal

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7
Q

At what level is free plasma [Ca 2+ ] maintained?

A

Within the narrow range of 1.0-1.3mmol/L

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8
Q

Where does phosphate play a critical role?

A

In cellular energy metabolism

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9
Q

Why does phosphate play a critical role in cellular energy metabolism?

A

Because it’s part of the adenosine triphosphate molecule

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10
Q

Other than in ATP, where else does phosphate play a crucial role?

A

In activation and deactivation of enzymes

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11
Q

How does regulation of plasma phosphate differ from calcium?

A

It is less tightly regulated, and the levels fluctuate throughout the day, particularly after means

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12
Q

Why are calcium homeostasis and phosphate homeostasis intimately linked?

A
  • Because calcium and phosphate are the principal components of hydroxyapatite crystals
  • They are regulated by the same hormones
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13
Q

What is the formula for hydroxyapatite crystals?

A

Ca 10 (PO 4 ) 6 (OH) 2

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14
Q

What do hydroxyapatite crystals constitute?

A

The major portion of the mineral phase of bone

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15
Q

What hormones regulate calcium and phosphate?

A

Primarily parathyroid hormone (PTH) and 1,25-dihydroxyvitamin D (calcitrol), and, to a lesser extent, calcitonin

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16
Q

Where do PTH, calcitriol and calcitonin act?

A

The organ systems of bone, kidney and GI tract

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17
Q

What is the purpose ofPTH, calcitriol and calcitonin?

A

To control the levels of calcium and phosphate ions in the plasma

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18
Q

Why are the actionsPTH, calcitriol and calcitonin on calcium and phosphate typically said to be opposed?

A

A particular hormone may elevate the level of one ion while lowering the other

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19
Q

Where is calcium location?

A

Within bone

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20
Q

How much calcium is in the bone?

A

~1kg

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21
Q

What is the total amount of calcium in the extracellular pool?

A

Only a fraction of the amount in bone, about 1g

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22
Q

What is the typical daily dietary intake of calcium?

A

~800 to 1200mg

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23
Q

What are the major dietary sources of calcium?

A

Dairy products

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24
Q

What do the intestines do regarding calcium?

A
  • Absorb ~half of the dietary calcium (~500mg/day)
  • Secrete calcium for removal from body (~325mg/day)
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25
Q

What is the net intestinal uptake of calcium?

A

About 175mg/day

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26
Q

What happens to bone in a steady state?

A

Calcium deposition in bone of about 280mg/day is matched by an equal amount of calcium reabsorption

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27
Q

How much calcium to the kidneys filter a day?

A

10 times the total extracellular pool of calcium, about 10,000mg/day

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28
Q

What happens to 98% of the pool that is filtered by the kidneys?

A

It’s reabsorbed

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29
Q

What is the net renal excretion of Ca 2+ ?

A

Less than 2% of the filtered load

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30
Q

What happens regarding kidney filtering in a person in calcium balance?

A

Urinary excretion (~175mg/day) is the same as net absorption by the GI tract

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31
Q

How does calcium exist in plasma?

A
  • As free ionised species
  • Associated with anionic sites on serum proteins, especially albumin
  • Complexed with a low-molecular-weight organic anion
32
Q

Give 2 examples of low-molecular-weight organic anions calcium may be complexed with?

A

NAME?

33
Q

What is the total concentration of all three physiochemical forms of calcium in the plasma?

A

Normally 2.2-2.7mmol/L

34
Q

How much calcium is free in healthy individuals?

A

~45%

35
Q

How much calcium is bound to proteins in healthy individuals?

A

~45%

36
Q

How much calcium is bound to small organic anions in healthy individuals?

A

10%

37
Q

What form of calcium is most important with regard to regulating the secretion of PTH?

A

Ionised form

38
Q

What is the ionised form of calcium involved in?

A

Most of the biological actions of calcium

39
Q

What do common laboratory tests measuring calcium usually measure?

A

Total calcium, including not only physiologically active free ionised calcium, but calcium bound to albumin and other proteins

40
Q

How is it determined if free calcium is in the correct range or not?

A

The levels are corrected depending on the level of albumin

41
Q

What is hypocalcaemia?

A

When calcium levels are too low

42
Q

What is the consequence of hypocalcaemia?

A

Hyper-excitablity of the nervous system, including the neuromuscular junction, leading to parasthesia

43
Q

What does paraesthesia lead to?

A

Tetany, paralysis and convulsions

44
Q

What is hypercalcaemia?

A

Calcium too high

45
Q

What are the consequences of hypercalcaemia?

A

Formation of kidney stones, constipation, dehydration, kidney damage, tiredness and depression

46
Q

What is it clear from the consequences of dysregulation of serum calcium?

A

That it’s very important that levels are maintained within set limits

47
Q

What are the two key hormones in calcium regulation?

A
  • PTH
  • Calcitriol
48
Q

What do PTH and calcitriol both act to do?

A

Raise serum calcium concentrations

49
Q

How do PTH and calcitriol differ?

A

They act by different mechanisms, and over different time scales

50
Q

What is the short term regulation of serum calcium under control of?

A

PTH

51
Q

What is long term regulation of serum calcium under control of?

A

Calcitriol

52
Q

What is vitamin D?

A

A collective term for a group of prohormones

53
Q

What are the 2 major forms of vitamin D?

A
  • D2 (ergocalciferol)
  • D3 (cholecalciferol)
54
Q

Where is vitamin D obtained from?

A

NAME?

55
Q

Is vitamin D reactive?

A

No, it’s biologically inert

56
Q

What must happen for vitamin D to be activated in the body?

A

Two hydroxylation reactions

57
Q

What is calcitriol?

A

An active form of vitamin D found in the body, involved in calcium regulation

58
Q

Other than the prohormones, what else is the term vitamin D used to refer to?

A

The metabolites of vitamin D, and other analogues of these substances

59
Q

What is parathyroid hormone related peptide (PTHrP)?

A

A peptide

60
Q

What produces PTHrP produced by?

A

Tumours

61
Q

What may production of PTHrP lead to?

A

Hypercalcaemia

62
Q

Where can the measurement of PTHrP be useful?

A

In determining the cause of an otherwise unexplained hypercalcaemia

63
Q

What does the secretion of PTHrP from cancer cells lead to?

A

Humeral hypercalcaemia of malignancy (HHM)

64
Q

Where is PTHrP commonly produced?

A

In patients with breast or prostate cancer, and occasionally in patients wiht myeloma

65
Q

What does PTHrP share with PTH

A

Many actions

66
Q

What does the similarities in action of PTH and PTHrP lead to?

A
  • Increased calcium release from bone
  • Reduced renal calcium excretion
  • Reduced renal phosphate reabsorption
67
Q

What activity does PTHrP not increase?

A

C-1 hydroxylase

68
Q

What is the result of PTHrP not increasing renal C-1 hydroxylase activity?

A

It doesn’t increase calcitrol concentration, unlike PTH

69
Q

What does calcitonin do?

A

In an animal, lowers serum calcium levels

70
Q

What does calcitonin do in humans?

A

Little function

71
Q

What suggests that calcitonin has little function in humans?

A

It appears to lack pathology associated with either hypo or hyper secretion

72
Q

Where is calcitonin secreted from?

A

Thyroid gland

73
Q

What happens if the thyroid gland is removed or destroyed, regarding calcitonin?

A

The lack of secretion appears to have no effect on calcium homeostasis

74
Q

Where might calcitonin be important?

A

In pregnancy

75
Q

Why may calcitonin be important in pregnancy?

A

May serve to preserve maternal skeleton

Z OLD ESA 1- Metabolism (17 decks)

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