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Physiology > Calcium Metabolism > Flashcards

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
Q

Net effect of PTH on bone

A
  • increased serum Ca

- increased serum P

26
Q

PTH stimulates calcium reabsorption from the ______ and _____ (fine tuning)

A

Distal tubules; collecting ducts

27
Q

_______ stimulates P excretion

A

Proximal tubules
- has more of an impact that resorption of bone!!!!
= overall decrease in phosphorous concentration

28
Q

Net effect of PTH on kidneys

A
  • increase serum Ca

- decrease serum P

29
Q

Proximal tubules stimulates synthesis of _____

A

Active form of vitamin D

- increases activity of 1-alpha hydroxylase to catalyze vitamin D reaction

30
Q

What is the net effect of PTH in the blood?

A
  • increase calcium

- decrease phosphorous

31
Q

Hyperparathyroidism

A
  • increase calcium
  • decrease phosphorous
  • use to differentiate causes of hypercalcemia*
32
Q

What are the inactive and active forms of Vitamin D?

A
  • inactive: cholecalciferol

- active: calcitriol

33
Q

Animals mainly rely on _____ to get vitamin D

A

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
Q

Calcitriol effect on the small intestine

A
  • increase calcium

- increase phosphorous

35
Q

Calcitriol target tissues

A
  • small intestine
  • bone
  • parathyroid: decrease PTH via feedback inhibition
36
Q

Nuclear transcription factor

A
  • 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
Q

Small quantities of calcitriol

A
  • increases bone calcification

- increases calcium deposition in bone

38
Q

Large quantities of calcitriol

A
  • stimulates bone resorption

- increases Ca and P in blood

39
Q

Ability of PTH to cause bone resorption is reduced/prevented _______ 1,25 vitamin D

A

Without!!

40
Q

Calcipotriene toxicity

A

Derivative of calcitriol

  • used for psoriasis
  • dogs can eat it = max increase in Ca and P
41
Q

PTH regulation

A

Feedback inhibition

- does not involve pituitary or hypothalamus

42
Q

Secretion is decreased by

A
  • hypercalcemia

- calcitriol

43
Q

Secretion is increased by

A
  • hypocalcemia

- hyperphosphatemia

44
Q

Hepatic activation is decreased in response to

A
  • 25-(OH)D (feedback inhibition)
  • conserves vitamin D stores in liver
  • prevents excessive activation of vitamin D
  • 25a-hydroxylase*
45
Q

Renal activation

A

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
Q

PTH increases in response to

A
  • decreased calcium

- increased phosphorous

47
Q

PTH decreases in response to

A
  • increased calcium

- increased calcitriol

48
Q

Target tissues of PTH

A 
Kidney
- resoprtion: increased Ca
- excretion: decreased P
Small intestine
- increased calcitriol
- increased Ca and P
Bone
- resorption
- increased Ca and P
49
Q

Calcitriol regulation

A
  • renal activation via 1a-hydroxylase
  • increases in response to increase PTH, decrease P
  • decreases in response to increased P
50
Q

Calcitriol target tissues

A 
Small intestine
- CBP: increased Ca and P
Bone
- variable
Parathyroid
- decrease PTH
51
Q

Parafollicular cells of thyroid ______ Ca concentrations

A

Decrease

52
Q

Calcitonin

A

Opposite effects of PTH

  • decreases osteocytic membrane activity and osteroclast formation
  • less significant than PTH

Physiology (33 decks)

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