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NYCC MSP > Calcium & Phosphorus > Flashcards

Calcium & Phosphorus Flashcards

1
Q

Name the fundamental roles of calcium

A
  • major cation in bone & teeth
  • neurotransmission (synapse)
  • skeletal/cardiac/smooth m contraction
  • enzymatic reactions
  • hormone secretion/mediator
  • blood clotting
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2
Q

Most calcium is found in ____

A

bone

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3
Q

Name 3 forms of calcium

A
  • ionized (50%)
  • bound to proteins (41%)
  • combined with anions (9%)
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4
Q

What form of calcium is biologically active (what we use)?

A

Ionized

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5
Q

What is the normal range of calcium levels in the plasma?

A

8.6-10.6 mg/dl

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6
Q

What term would describe a patient that has a calcium serum level of 11.3 mg/dl?

A

Hypercalcemia

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7
Q

What term would describe a patient that has a calcium serum level of 8.0 mg/dl?

A

Hypocalcemia

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8
Q

Calcium is a nervous system ____

A

depressant

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9
Q

What is the major cation in bone?

A

calcium

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10
Q

What is the major anion in bone?

A

phosphate

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11
Q

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

A

hydroxyapatite

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12
Q

What is the normal range of phosphate levels in the plasma?

A

3-4.5 mg/dl

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13
Q

The gut wall has ____ absorption of calcium

A

poor
(absorb 350mg/day, excrete 250mg/day)

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14
Q

In terms of urinary excretion, most calcium is ____ here

A

resorbed
(90% prox, 10% distal)

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15
Q

Calcium resorption is ____ dependent

A

hormone
(serum calcium levels)

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16
Q

Dietary phosphorus is ____ absorbed across the gut wall due to ____

A
  • readily
  • calcium binding
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17
Q

When phosphorus levels are below 1mmol/L, what do the kidneys do with phosphate?

A

resorb ALL phosphate

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18
Q

When phosphorus levels are above 1mmol/L, what do the kidneys do with phosphate?

A

excretes via overflow mechanism (excretion = excess)

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19
Q

What hormone is consider the major regulator of plasma calcium and phosphorus levels?

A

Parathyroid hormone (PTH)

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20
Q

Secretion of PTH is ____ related to plasma Ca2+ levels

A

inversely

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21
Q

the release of PTH is monitored by Ca2+ sensing receptor (CaSR) on cell membrane of ____ gland cells

A

parathyroid

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22
Q

PTH & Ca2+ form a ____ feedback pair. as Ca2+ levels increase, PTH secretion ____

A

negative
decreases

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23
Q

____ Ca2+ regulates PTH secretion within minutes

A

ionized

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24
Q

What is the half life of PTH?

A

less than 20 mins

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25
Q

if sustained over time:
_______calcemia = shut down PTH synthesis & degrades stores (grandular atrophy)

________calcemia = cause gland hypertrophy

A

HYPERcalcemia
HYPOcalcemia

26
Q

What short term effects does PTH have on bones? (normal daily swing)

A
  • down regulate osteoblasts
  • release of calcium & phosphate by osteoblasts & osteocytes
27
Q

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

A
  • stimulate production of osteoclasts & activates resorption of bone
  • remove calcium phosphate salts from bone lying near these cells waiting to be mineralized
28
Q

What function does PTH have on the kidneys?

A
  • ^Ca2+ resorption from distal tubule
  • MOST dramatic: inhibit resorption of phosphate (less phosphate to bind Ca2+, increasing serum calcium)
  • stimulates synthesis of vit D metabolite -> ^PTH -> ^calcitriol
29
Q

What effect does calcitriol have on the kidney?

A
  • binds with cytosolic receptor and enters nucleus
  • stimulates synthesis of calbindin
30
Q

What effect does calcitriol have on the gut?

A

facilitates Ca2+ absorption
(phosphate absorption also stimulated by vit D)

31
Q

What effect does calcitriol have on bone?

A
  • stimulates bone resorption working synergistically with PTH
  • receptor on osteoblasts promotes formation of osteoclasts
  • receptor for calcitriol found in osteoclasts to increase activity
32
Q

PTH has an indirect action on the gut via _____ & _____ production & release (kidney). Calbindin facilitates active transport of ____ across the gut wall

A
  • calcitriol & calbindin
  • Ca2+
33
Q

Are there receptors for PTH in cells of gut wall?

A

no

34
Q

PTH causes prompt increase of _____ & decreases of _____ in the plasma

A

Ca2+
phosphate

35
Q

as plasma levels of Ca2+ rise, PTH levels ____, kidney excretes ____ Ca2+ & urinary Ca2+ levels achieve equilibrium to maintain homeostasis

A

decrease
more

36
Q

All actions of PTH on the parathyroid, kidney & gut ____ Ca2+ influx into blood

A

increase

37
Q

As PTH levels increase, plasma phosphate levels ____, but it is overwhelmed by the action of PTH on the ____ causing…

A
  • increase
  • kidney
  • elimination of phosphate in the urine
38
Q

What is the indirect role of phosphate on PTH?

A

lowers Ca2+ levels through physiological mechanisms:
- increases renal excretion of Ca2+
- Ca2+ binds with PO4-
–> Ca2+ drops, PTH increases

39
Q

What is the purpose of increased Ca2+ excretion with increased phosphate levels?

A

PREVENT metastatic calcification
(seen in hyperparathyroidism)

40
Q

How does PTH modulate hyperphosphatemia?

A

increases renal excretion of phosphate

41
Q

What function does calbindin have on the body?

A

Increases calcium absorption in the gut (binds Ca2+ in gut)

42
Q

What term would describe a patient that has a serum phosphate level of 5.2 mg/dl?

A

Hyperphosphatemia

43
Q

What term would describe a patient that has a serum phosphate level of 1.9 mg/dl?

A

Hypophosphatemia

44
Q

What would happen to Ca2+ and PTH levels if there is an increased phosphate level in the blood?

A

Calcium drops and an increase in PTH

45
Q

What effect does vitamin D have on Calcium in the gut?

A

potent effect of increasing Ca2+ absorption

46
Q

What must we have to build bone, which also has an important effect on bone resorption via its role in Ca2+ metabolism?

A

vitamin D

47
Q

What is the major storage site for vitamin D?

A

muscle

48
Q

profound muscle ____ is seen with vitamin D deficiency

A

weakness

49
Q

Where is vitamin D converted to more metabolically active metabolites?

A

Liver & kidney

50
Q

If PTH is increased, what is vitamin D converted to in the kidney?

A

calcitriol
(1-25(OH)2D3)

51
Q

If PTH is decreased, what is vitamin D converted to in the kidney?

A

24-25(OH)2D3

52
Q

Where is calcitonin produced?

A

parafollicular cells of thyroid gland

53
Q

Calcitonin acts to ____ plasma Ca2+

A

lower

54
Q

Calcitonin is a PTH ____

A

antagonist (does the opposite)

55
Q

What is the mechanism of action of calcitonin on calcium?

A
  • binds to membrane receptors -> ^cAMP
  • cAMP initiates calcitonin action
  • sequesters Ca2+ into mitochondria, reducing serum levels (pulls Ca into cells)
56
Q

What effect does calcitonin have on osteoclasts?

A

inhibition of osteoclasts (bone resorption)

57
Q

What effect does calcitonin have on phosphate?

A

enhances phosphate uptake into bone
(same result as PTH on phosphate, different mechanism)

58
Q

____ “tries” to conserve Ca2+ (^Ca serum levels)

A

calcitriol

59
Q

____ binds Ca2+ in the gut (^Ca absorption

A

calbindin

60
Q

____ “tones down” levels of Ca2+ (decrease Ca serum)

A

calcitonin

NYCC MSP (22 decks)

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