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Musculoskeletal Physiopathology > Calcium and Phosphorus Metabolism > Flashcards

Calcium and Phosphorus Metabolism Flashcards

1
Q

Where is calcium found in the body?

A
  • 1% is in the cells and organelles
  • .1% is in extracellular fluid
  • 98.9% is in bone
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2
Q

50% of calcium in the body is found in what form?

A

Ionized Ca2+

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3
Q

Which form of calcium is biologically active?

A

Ionized Ca2+

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4
Q

41% of calcium in the body is found in what form?

A

Bound to proteins:

  • Typically albumins
  • Cannot diffuse through capillary walls
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5
Q

9% of calcium in the body is found in what form?

A

Combined with anions:

  • Citrate, phosphate, bicarbonate
  • NOT ionized
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6
Q

How much of calcium in the body is biologically active?

A

50% Ionized Ca2+

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7
Q

What is a normal level of calcium in the body?

A

9.4mg/dl (range 8.6-10.6)

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8
Q

Why is calcium mg/dl very tightly controlled?

A

Very small changes can have a drastic effect

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9
Q

What is the effect of hypercalcemia?

A

Depresses the nervous system:

  • Excess calcium shuts down the sodium-calcium pumps in nerves
  • Weakness, flaccid paralysis
  • Anorexia, constipation
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10
Q

What is the effect of hypocalcemia?

A

Creates spontaneous nerve firing:

  • Insufficient calcium increases sodium concentrations in nerves
  • Spasm, tetany, seizures
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11
Q

Calcium is a major ___-ion in bone and teeth

A

cation

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12
Q

Phosphate is a major ___-ion in bone

A

anion

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13
Q

Which mineral is fundamentally important in:

  • All glycolytic compounds
  • ATP, ADP, AMP, creatine phosphate
A

Phosphate

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14
Q

Which mineral is fundamentally important in:

  • Neurotransmission
  • Skeletal/cardiac/smooth muscle contraction
A

Calcium

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15
Q

Which mineral is fundamentally important in:

  • Enzymatic reactions
  • Hormone secretion; mediates hormone events
  • Blood clotting
A

Calcium

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16
Q

Which mineral is fundamentally important in:

  • Cofactors - NAD, NADPH
  • Lipids like phosphatidyl choline
  • Covalent modifier of enzymes
A

Phosphate

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17
Q

The majority of calcium and phosphate is tied up together in ___

A

hydroxyapatite Ca10(PO4)6(OH)2

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18
Q

What is the normal level of phosphate in the body?

A

3-4.5 mg/dl

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19
Q

Why aren’t phosphate levels as tightly controlled as calcium?

A

Larger variations are needed before any symptoms

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20
Q

Where is phosphate found in the body?

A
  • 85% is in bone
  • 14% is in cells
  • 1% is in extracellular fluid
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21
Q

How much dietary calcium should be consumed?

A

About 1000mg of calcium/day

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22
Q

How much dietary calcium should be excreted?

A

About 1000mg of calcium/day (900mg in feces, 100mg in urine)

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23
Q

Which vitamin is essential for the gut wall to absorb calcium?

A

Vitamin D

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24
Q

How much calcium is absorbed by the gut wall?

A

About 350mg/day

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25
Q

How much calcium is excreted by the gut wall?

A

About 250mg/day

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26
Q

90% of calcium in excreted urine is reabsorbed in…

A

proximal filtrate

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27
Q

10% of calcium in excreted urine is reabsorbed in ___

A

distal filtrate (depending on serum calcium levels)

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28
Q

Dietary phosphorus is readily absorbed ___ due to ___

A

readily absorbed across the gut wall due to calcium binding

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29
Q

Phosphorus is excreted in urine via ___

A

overflow mechanism

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30
Q

When concentrations are below 1mmol/L, kidneys reabsorb all ___

A

phosphate

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31
Q

Above 1mmol/L, ___ excretes via overflow mechanism

A

phosphate

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32
Q

Excretion of phosphate above 1 mmol/L is equal to ___

A

excess phosphate

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33
Q

Parathyroid hormone can greatly increase ___ excretion

A

phosphate

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34
Q

Phosphate control is mainly via ___

A

urinary excretion

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35
Q

Ca2+ movement between bone, gut, and kidneys is regulated by:

A
  • Parathyroid Hormone (PTH)
  • Calcitriol or Vitamin D
  • Calbindin
  • Calcitonin
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36
Q

Secretion of PTH is inversely related to ___

A

plasma Ca2+ levels

37
Q

Release of PTH is monitored by ___ on cell membrane of parathyroid gland cells

A

Ca2+ sensing receptor

38
Q

PTH and ___ form a negative feedback pair

A

PTH and Ca2+

39
Q

As Ca2+ levels increase, PTH secretion ___

A

decreases

40
Q

As PTH secretion increases, Ca2+ levels ___

A

decrease

41
Q

What form of calcium regulates PTH secretion (within minutes)?

A

Ionized Ca2+

42
Q

What is the half life of PTH?

A

Less than 20 minutes

43
Q

How does hypercalcemia affect the parathyroid gland?

A

PTH synthesis is shut down and stores are degraded (glandular atrophy)

44
Q

How does hypocalcemia affect the parathyroid gland?

A

Gland hypertrophy

45
Q

What are the short term effects of PTH on bone?

A
  • Downregulate osteoblasts
  • Release of calcium and phosphate by osteoblasts and osteocytes

(reminder: PTH has a 20 minute half life)

46
Q

What are the long term effects of PTH on bone (persistent hypocalcemia)?

A
  • Stimulate production of osteoclasts and activates resorption of bone
  • Remove calcium phosphate salts from bone lying near these cells waiting to be mineralized
  • All constituents of bone are liberated
47
Q

Which constituents of bone are liberated by long term effects of PTH?

A
  • Calcium
  • Phosphate
  • Bicarbonate
  • Other minerals and proteins
48
Q

How does PTH affect the proximal and distal tubules of kidneys?

A
  • Increase Ca2+ resorption from distal tubule
  • Proximal tubule is very consistent, barring renal disease
49
Q

What is the most dramatic effect of PTH on the kidneys?

A

Inhibit resorption of phosphate; less phosphate to bind Ca2+, increasing serum calcium

50
Q

PTH stimulates synthesis of ___ in the kidney

A

Calcitriol, a Vitamin D metabolite

51
Q

What is the action of calcitriol in the kidneys?

A

Binds with cytosolic receptor and enters nucleus; stimulates protein synthesis of calbindin

52
Q

What is the action of calbindin in the gut?

A

Facilitates Ca2+ absorption

53
Q

Calcium absorption across the gut is facilitated by ___

A

calbindin

production stimulated by calcitriol

54
Q

Phosphate absorption across the gut is stimulated by ___

A

vitamin D

55
Q

What is the action of calcitriol in bone?

A

Stimulates bone resorption working with PTH

PTH stimulates synthesis of calcitriol

56
Q

How does calcitriol affect osteoblasts?
How does calcitriol affect osteoclasts?

A

Osteoblast receptors for calcitriol are signaled to form osteoclasts
Osteoclast receptors for calcitriol are signaled to increase activity

57
Q

The gut is affected by PTH indirectly via ___

A

calcitriol and calbindin production and release (from kidneys)

PTH makes these

58
Q

___ facilitates active transport of Ca2+ across the gut wall

A

Calbindin

59
Q

Calbindin facilitates active transport of ___ across the gut wall

A

Ca2+

60
Q

PTH causes increase of ___ and decrease of ___ in plasma

A

increase of calcium and decrease of phosphate in plasma

61
Q

How do the kidneys initially react to phosphate and calcium (prompted by PTH)?

A

Kidney dumps phosphate and conserves calcium initially

62
Q

As plasma calcium levels rise and PTH levels decrease, how does the kidney react?

A

Kidney excretes more calcium so urinary calcium levels maintain homeostasis

63
Q

Actions of PTH on parathyroid, kidney, and gut increase ___ influx into blood

A

calcium

64
Q

How does PTH affect the kidney when plasma phosphate levels also rise?

A

PTH action on the kidney overwhelms phosphate levels causing elimination of phosphate in the urine

65
Q

How is phosphate indirectly related to PTH?

A

Role of phosphate on PTH is indirect through mechanisms that lower calcium levels

66
Q

With increased phosphate, ___ is excreted in urine

A

calcium

67
Q

Increased phosphate leads to ___ dropping due to binding with phosphate, leading to ___ increasing and preventing ___

A

calcium dropping due to binding with phosphate, leading to PTH increasing and preventing metastatic calcification

68
Q

___ modulates hyperphosphatemic situations by increasing renal excretion of phosphate

A

PTH

69
Q

PTH modulates phyperphosphatemic situations by what effect on the kidney?

A

Increasing renal excretion of phosphate

70
Q

Vitamin D has a potent effect of increasing ___ absorption from the gut

A

calcium

71
Q

___ has a potent effect of increasing calcium absorption from the gut

A

Vitamin D

72
Q

How is Vitamin D necessary to bone?

A

Needed to build bone, also important in bone resorption via its role in calcium metabolism
May play a role in bone remodeling as inflammatory mediator

73
Q

What is a major storage site for Vitamin D?

A

Muscle

74
Q

Profound muscle weakness is seen in ___ deficiency

A

Vitamin D

75
Q

Vitamin D is converted to more metabolically active metabolites in the:

A
  • Liver
  • Kidney
76
Q

Vitamin D is stored in the kidney as ___

A

calcitriol

77
Q

What gland cells produce calcitonin?

A

Parafollicular cells of the thyroid gland

78
Q

Calcitonin acts to lower plasma ___

A

calcium

79
Q

What is the relationship between calcitonin and PTH?

A

Calcitonin is a PTH antagonist

80
Q

Calcitonin binds to membrane receptors (in all cells of the body) causing ___ levels to increase

A

cAMP (cyclic adenosine monophosphate)

81
Q

cAMP as second messenger initiates ___ action

A

calcitonin

82
Q

Calcitonin sequesters calcium into ___, reducing serum levels

A

mitochondria

83
Q

How does calcitonin lower plasma levels of calcium?

A

Lowers cytosolic calcium, pulling calcium into cells (mitochondria)

84
Q

Which bone cells are inhibited by calcitonin?

A

Osteoclasts (because there’s less calcium available in the blood); this is the opposite effect of PTH

85
Q

Calcitonin has the same results as PTH on ___

A

phosphate

86
Q

How is calcitonin’s effect of phosphate different from PTH’s effect?

A
  • Mechanism is different
  • Calcitonin enhances phosphate uptake into bone
87
Q

Basically, what is the effect of calcitriol on calcium?

A

Tries to conserve calcium; increases calcium in serum

88
Q

Basically, what is the effect of calbindin on calcium?

A

Binds calcium in gut; increases calcium absorption

89
Q

Basically, what is the effect of calcitonin on calcium?

A

Tones down levels of calcium; decreases calcium in serum

Musculoskeletal Physiopathology (31 decks)

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