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Endocrinology > Physiology of Ca-regulation hormones > Flashcards

Physiology of Ca-regulation hormones Flashcards

1
Q

What is the most common cause of osteoporosis?

A

involution

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2
Q

What phase in bone develop has the sharpest decline?

A

Phase 2 in women (after menopause)

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3
Q

Where is 99% of the Ca? Where is the remaining 1%

A

Bone; .1 in extracellular, 1% intracellular

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4
Q

__% of Ca is free in the plasma and is regulated by hormones.

A

45-50%

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5
Q

How much Ca is anion bound? How much is protein bound?

A

6-9; 40-45

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6
Q

What is the normal range of Ca in the blood?

A

8.5-10.5

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7
Q

____ causes nervous system excitement and tetany.

A

Hypocalcemia

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8
Q

How is most of the ingested Ca eliminated?

A

Feces

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9
Q

What secretes PTH?

A

Chief cells

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10
Q

What secretes calcitonin

A

C cells of thyroid gland

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11
Q

Chemical structure of PTH

A

polypeptide with 84aa

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12
Q

Chemical structure of calcitonin

A

polypeptide with 32 aa

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13
Q

What does PTH infusion do to calcium and phosphate levels?

A

Increase Ca, decrease PO4

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14
Q

Describe how total body Ca changes in a lifetime.

A

Increases with bone formation- till 20ish. Then decreases

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15
Q

How does low Ca cause tetany? What happens with high Ca?

A

Low Ca causes decreased threshold for voltage gates Na channels.
High Ca- Contraction of smooth muscle is suppressed.

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16
Q

Describe Ca exchange between intestines and ECF

A

Only about 1/3 is absorbed and the rest is excreted in the feces. Ca is also secreted into the intestine, for a net absorption of 100 mg/day. Most ingested Ca is excreted in feces

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17
Q

Describe Ca exchange between ECF and kidneys

A

Kidneys have the capacity to excrete a lot of Ca by reducing resorption but usually excrete 100 mg/day.

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18
Q

What is bone fluid and how is it separated from ECF?

A

Aqueous solution that immerses bone and contains Ca and PO4. Separated by an osteocytic membrane formed by osteocytes and osteoblasts.

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19
Q

Describe the rapid exchanges that occur between ECF and bone fluid

A

PTH lowers plasma PO4, Ca permeability is increased and osteocytic pump activity increased. This allows bone salts to move into ECF

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20
Q

Describe the slower exchanges that occur between ECF and bone fluid

A

PTH slowly increases formation and activity of osteoclasts which resorb bone, thereby releasing Ca.

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21
Q

Where are PTH receptors in bone?

A

osteoblasts

22
Q

How does PTH lead to osteoclast activation

A

PTH–> PTHR1 on osteoblasts–> express RANKL–> RANKL binds RANK on osteoclast precursor –> osteoclast gene transcription

23
Q

How does osteoprotegerin lead to osteoclast inhibtion?

A

Released by osteoblasts. Prevents binding of RANK to RANKL.

24
Q

____ decreases osteoprotegerin production. ____ stimulates it.

A

PTH;Estrogen

25
Q

When and how does PTH cause bone formation?

A

Low, intermittent doses enhance proliferation and decrease apoptosis of osteoblasts.

26
Q

How much Ca is filtered at the glomerulus?

A

50ish%… protein bound Ca can not be filtered

27
Q

Where is most of the Ca reabsorbed in the kidney? Minority?

A

90% from proximal tubule, loop of henle, early distal tubule.
10% from late distal tubule and collecting duct

28
Q

Where does PTH act at the nephron

A

PTH acts at the Proximal tubule to put Phosphate in Pee (4Ps)

Late distal tubule and collecting duct to increase Ca reabsorption

29
Q

ECF Ca changes are sensed by ______.

A

GPCR on chief cells (PT)

30
Q

Low calcium causes an ____ in PTH, which ___Mg and ____ PO4.

A

Increase in PTH
Decrease in Mg
Increase in PO4

31
Q

How does PTH affect intestinal absorption of Ca

A

Indirectly. It is required for conversion of 25 VD to 1,25 VD which then increases Ca absorption.

32
Q

What does calcitonin do to Ca and PO4?

A

Lowers Ca and PO4 via:

  • Bone: reduce reabsorption by inhibiting osteoclast and stimulating Ca deposition
  • Kidney: Inhibits reabsorption of Ca and PO4
33
Q

____ protects against calcium loss during times of Ca mobilization.

A

calcitonin

34
Q

Synthesis of VD

A 
Skin--> liver--> kidney
Skin: Pro-VD (7-dehydrocholesterol) --> cholecalciferol by UV light--> goes to liver
Liver: Hydroxylated to 25 OH -VD
At kidney: 25--> 1,25 OH-VD (calcitriol)
Mediated by 1a hydroxylase
- Increased by PTH
- Decreased by Ca and FGF23
35
Q

Peripheral actions of VD

A

Bone: resorption
Intestines: increase Ca absorption
Kidneys: increase Ca absorption
PTH: decrease synthesis of PTH

36
Q

What 3 things push VD synthesis to inactive 24,25 form?

A

Increase serum Ca, Increase 1,25 VD, increase FGF23

37
Q

What does Ca, PTH, and FGF23 do to VD synthesis towards 1,25 VD?

A

Ca: negative
PTH: positive
FGF23: Negative

38
Q

What is the major circulating form of vitamin D?

A

25(OH)D

39
Q

Decrease activity of 1a hydroxylase favors what?

A

hydroxylation to 24,25 OH-VD

40
Q

T or F. It takes big Ca changes to cause changes in VD levels.

A

False- slight decrease in Ca below normal causes big VD increase.

41
Q

What is hydroxyapatite?

A

complex precipitate of Ca and PO4 that is laid down in the protein osteoid matrix

42
Q

[Ca]x[PO4]>solubility product=?

A

bone deposition

43
Q

[Ca]x[PO4]<solubility product=?

A

bone resorption

44
Q

T or F. To increase/decrease bone mineralization you need an increase/decrease in both Ca and PO4.

A

False. Depends on product of Ca and PO4, so only one has to go up

45
Q

Phosphate lab numbers

A

Normal: 3-4.5
Kids normal: 4.5-6.5 due to bone growth
Approx 55% is free, 35% protein bound, 10% anion bound

46
Q

Distribution of total body phosphate

A

85% bone, .1% extracellular, 14% intracellular

47
Q

Where is phosphate excreted?

A

Mostly kidney but also come in feces

48
Q

What does phosphate do in someone on hemodialysis

A

positive potassium balance, deposits in vasculature

49
Q

What is the function of FGF23?

A

Acts at kidney to decrease the expression of Na/PO4 cotransporters, production of 1,25VD–> hypophosphatemia, reduce PTH

50
Q

What conditions cause secretion of FGF23 by bone?

A

increased levels of PO4, 1,25VD, and PTH

Endocrinology (31 decks)

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