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Calcium Metabolism Flashcards

1
Q

_____ of calcium is located in bones and teeth`

A

99%

- hydroxyapatite

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2
Q

How much calcium is intracellular?

A

1%

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3
Q

How much calcium is extracellular?

A
  1. 1% in ECF and plasma
    - 30-40% is protein-bound
    - ionized (50-60%) (unbound) –> biologically active form, fraction dependent on pH
    - complexed (10%) –> citrate, lactate, bicarb, phosphate
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4
Q

Ionized calcium makes up ____ of intracellular plasma

A

55%

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5
Q

3 functions of calcium

A
  • nerve impulses via membrane stabilization
  • muscle contraction via release of Ach and NMJ (affects skeletal, smooth, and cardiac)
  • coagulation
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6
Q

Clinical signs of hypocalcemia in dogs

A
  • due to stabilization of sodium channels
  • anxiety
  • tremors
  • tetanic concentration
  • seizures
  • paw chewing
  • facial rubbing
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7
Q

Phosphorus concentrations

A
  • 85% in bone
  • 15% intracellular (cell membrane, nucleotides)
  • <1% extracellular fluid (buffer)
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8
Q

Site of calcium regulation

A
  • GIT
  • kidney
  • bone
  • parathyroid gland
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9
Q

Hormones of calcium metabolism

A
  • PTH
  • vitamin D (active form)
  • calcitonin
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10
Q

How much calcium is excreted in the feces

A

90%

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11
Q

Bone is in constant _____

A

Equilibrium

  • balance of calcium resorption and deposition
  • calcium reservoir
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12
Q

______ of ingested Ca is absorbed thru the intestine

A

35%

- via activated calcitriol

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13
Q

Almost all dietary P is absorbed from the ___

A

Gut

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14
Q

Where does calcium reabsorption occur in the kidneys?

A

90% reabsorbed in the proximal tubules, loops of Henle and early distal tubules
- reabsorption of remaining 10% is selective!! –> dependent on blood ionized Ca concentration

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15
Q

Bone cells

A 
Osteoclasts
- monocyte derivatives
- bone resorption
Osteoblasts
- bone deposition
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16
Q

Vitamin D inhibits ________

A

Release of Ca from bone

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17
Q

Parathyroid hormone

A
  • chief cells of PT
  • maintains plasma ionized calcium concentration
  • regulates plasma phosphorous concentration
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18
Q

PTH and the set point

A

Set point is the calcium concentration required to produce half of the max inhibition of PTH secretion
- small change in [Ca] = large change in [PTH]

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19
Q

PTH effect on bone

A

Resorption, release of Ca, P from bone

  • effect on blood levels
  • increased blood calcium, increased phosphorous
  • rapid phase of bone resorption (min-hrs)
  • slow phase of bone resorption (days-weeks)
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20
Q

PTH effect on kidney

A

Reabsorption
- increased calcium
Excretion
- decreased phosphorous

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21
Q

PTH effect on small intestine

A

Indirectly increases active vitamin D

- increase Ca, increase P

22
Q

Rapid phase of bone resorption

A

Osteocytic membrane system

  • osteoblasts, osteocytes
  • bone fluid between osteoblast membrane and bone containing Ca and P salts
23
Q

Osteocytic pump

A

Pumps Ca from bone fluid to ECF

- activated by PTH

24
Q

Slow phase of bone resorption

A

Osteoclasts

  • requires activation and proliferation
  • days to weeks
25
Net effect of PTH on bone
- increased serum Ca | - increased serum P
26
PTH stimulates calcium reabsorption from the ______ and _____ (fine tuning)
Distal tubules; collecting ducts
27
_______ stimulates P excretion
Proximal tubules - has more of an impact that resorption of bone!!!! = overall decrease in phosphorous concentration
28
Net effect of PTH on kidneys
- increase serum Ca | - decrease serum P
29
Proximal tubules stimulates synthesis of _____
Active form of vitamin D | - increases activity of 1-alpha hydroxylase to catalyze vitamin D reaction
30
What is the net effect of PTH in the blood?
- increase calcium | - decrease phosphorous
31
Hyperparathyroidism
- increase calcium - decrease phosphorous * use to differentiate causes of hypercalcemia*
32
What are the inactive and active forms of Vitamin D?
- inactive: cholecalciferol | - active: calcitriol
33
Animals mainly rely on _____ to get vitamin D
Diet; due to heavy fur content - liver is responsible for synthesizing digested vitamin D - proximal tubules of kidney is responsible for synthesizing it to active form
34
Calcitriol effect on the small intestine
- increase calcium | - increase phosphorous
35
Calcitriol target tissues
- small intestine - bone - parathyroid: decrease PTH via feedback inhibition
36
Nuclear transcription factor
- binds DNA - increase formation of calcium binding protein (on brush border of intestinal epithelia) - increases Ca - increases P * takes 2 days to take effect due to time it takes to get to the tip of the villi
37
Small quantities of calcitriol
- increases bone calcification | - increases calcium deposition in bone
38
Large quantities of calcitriol
- stimulates bone resorption | - increases Ca and P in blood
39
Ability of PTH to cause bone resorption is reduced/prevented _______ 1,25 vitamin D
Without!!
40
Calcipotriene toxicity
Derivative of calcitriol - used for psoriasis - dogs can eat it = max increase in Ca and P
41
PTH regulation
Feedback inhibition | - does not involve pituitary or hypothalamus
42
Secretion is decreased by
- hypercalcemia | - calcitriol
43
Secretion is increased by
- hypocalcemia | - hyperphosphatemia
44
Hepatic activation is decreased in response to
- 25-(OH)D (feedback inhibition) - conserves vitamin D stores in liver - prevents excessive activation of vitamin D * 25a-hydroxylase*
45
Renal activation
Most important site of vitamin D regulation!! - 1a hydroxylase - increases in response to increased PTH and decreased P - decreases in response to decrease P
46
PTH increases in response to
- decreased calcium | - increased phosphorous
47
PTH decreases in response to
- increased calcium | - increased calcitriol
48
Target tissues of PTH
``` Kidney - resoprtion: increased Ca - excretion: decreased P Small intestine - increased calcitriol - increased Ca and P Bone - resorption - increased Ca and P ```
49
Calcitriol regulation
- renal activation via 1a-hydroxylase - increases in response to increase PTH, decrease P - decreases in response to increased P
50
Calcitriol target tissues
``` Small intestine - CBP: increased Ca and P Bone - variable Parathyroid - decrease PTH ```
51
Parafollicular cells of thyroid ______ Ca concentrations
Decrease
52
Calcitonin
Opposite effects of PTH - decreases osteocytic membrane activity and osteroclast formation - less significant than PTH

Physiology (33 decks)

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