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Endo > Phys of Ca-Regulating Hormones (Fan) > Flashcards

Phys of Ca-Regulating Hormones (Fan) Flashcards

1
Q

physiologic roles of Ca

A 
Bonne growth/remodeling
Secretion (excitation coupled)
Contraction 
Action Potentials
Cofactors for Enzymes
Secondary messangers
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2
Q

What age does out total body calcium peak? Significance?

A

25; risk of osteoporosis increases with age

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3
Q

Describe the distribution of Ca in the body

A

99% in bone
1& Intracellular
.1% extracell (inc plasma)

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4
Q

Describe the distribution of Ca in the blood

A

Free > proteins bound&raquo_space; anion bound

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5
Q

What is the normal mM/L for Ca in the blood

A

10 mg/dl or 2.5 mM/L

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6
Q

hypocalcemia is defined as …

hypercalcemia is defined as …

A

10/5 mg/dl

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7
Q

When ECF [Ca++] falls below normal, the nervous system becomes (less or more excitable)
How far below normal does Ca have to fall for this to happen

A

more

<50% of nml

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8
Q

What happens when [Ca++] falls below 50% of nml

A

muscle spontaneously discharge impulses → tetanic muscle contraction

TETANY

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9
Q

WHat effect does severe hypocalcemia have on cardiac muscle?

A

long QT and arrhythmias

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10
Q

How is Ca excreted

A

feces&raquo_space; urine

*but kidneys do have a large capacity to excrete urine by reducing tubular reabs (55% filtered and ~90% reabs)

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11
Q

PTH is secreted by …

A

chief cells of the parathyroid gland

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12
Q

WHat produces calcitonin

A

C cells in thyroid gland

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13
Q

structual diff of PTH and calcitonin

A

PTH = 84 aa and Calcitonin = 32 aa

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14
Q

PTH (↓ or ↑) Ca in blood by…

A

↑ Ca by …
↑ release from bone
↑ reabs/↓secretion from kidney

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15
Q

PTH (↓ or ↑) PO4 in blood by…

A

↓PO4 by ↑excretion/↓reabs via kidneys

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16
Q

How long after PTH infusion will Ca/PO4 levels change

A

immediately

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17
Q

Describe how PTH effects Ca and PO4 is exchange between the bone fluid and ECF

A
  1. ↑formation and activity of ostoclast →↑bone reabs → ↑Ca and ↑PO4 released into bone fluid
  2. ↑ activity of Ca pump on osteocyte and blast membranes and ↑ permeability of their membranes → movement of Ca from bone fluid into ECF
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18
Q

Describe the effect of PTH on osteoclasts

A

PTH bind PTHR1 on osteoblasts → ↑RANKL and ↓OPG on osteoblasts → RANKL bind RANK in osteoclast precursor → activation of osteoclasts gene trcpt and diff → mature osteoclast → ↑bone reabs → ↑Ca in plasma

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19
Q

OPG is secreted by ____ and its effect is to _____

A

secreted by osteoblasts to inhibit osteoclast formation/bone reabsoption

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20
Q

effect of PTH on OPG production

A

↓

21
Q

What stimulates OPG production

A

estrogen

22
Q

effect of LOW dose PTH on osteoclasrs

A

↑ osteoblast prolif/differentiation and ↓ apoptosis of osteoblasts → ↑bone formation

(via PTHR on osteoblasts)

23
Q

Describe effect of PTH on renal kidney

A

inc reabs of Ca by 10-15% → 99% of Ca that is filtered is reabsorbed and only 1% is excreted

24
Q

How much Ca is filtered at the glomerulus? Why is some not freely filtered?

A

55% bc the other 40% is bound to plasma proteins and is not filterable

25
Q

T or F: it take a big inc or dec in Ca levels to see an response in PTH or calcitonin levels

A

F: small change!!!

26
Q

Changes in ECF [Ca] are sensed by…

A

GPCR on parathyroid chief cells to ↑or↑ PTH secretion

↑Ca are sensed by Ca sensing receptor
↓Ca are sensed by Relaxed Ca sensor

27
Q

Effect of ↑PTH on vit D

A

PTH is needed to convert 25-vit D to 1,25-vit D

28
Q

Calcitonin ↑ or ↓ Ca levels? PO4 levels?

How

A

↓Ca and ↓PO4

inhibit osteoclasts → ↓bone reabs
inhibits reabs of Ca in kidney

29
Q

Function of Calcitonin

A

protects against Ca loss from skeleton during periods of Ca mobilization (pregnancy, lactation, being a child)

30
Q

Calcitonin is used pharmacologically to treat

A

osteoporosis

31
Q

Describe Vit D synthesis

A

Cholecalciferol (UV rxn) or Ergocalciferol (diet) go to liver → liver makes 25(OH)vitD → kidney converts it to 1,25(OH)2vitD (if PTH is there/low Ca)

32
Q

Describe the effects of vit D in the body

A

↑ Ca absorption in GI
↓ Ca reabs in kidney
↑ bone resorption
↓ PTH synthesis (feedback)

33
Q

Where does the control of vit D synthesis occur? Explain

A

kidney:

  • if high Ca, 24alpha-hydroxylase is active and converts 25(OH)vitD to inactive 24,25(OH2)vitD
  • also active by 1,25vitD (feedback), FGF23

-if Ca low + PTH, 1alpha-hydroxylase is active and converts 25(OH)vitD to 1, 25(OH)2vitD

34
Q

______ in skin is converted to Cholecalciferol via UV light

A

7-dehydrocholesterol (provitamin D)

35
Q

A slight dec in [Ca] below normal, causes increased formation of _____

A

1,25(OH2)D

36
Q

complex precipitate of Ca and PO4

A

hydroxyapatite

37
Q

What determines whether Ca or PO4 are laid down or resorbed from bone?

A

product of their concentrations

NOT on their individual concs*

38
Q

Ca x PO4 > solubility product →

A

bone deposition

39
Q

Ca x PO4 < solubility product →

A

bone reaorption

40
Q

inc in Ca or PO4 in the ECF would …

A

inc bone mineralization/deposition

41
Q

normal levels of PO4 in blood

A

4 mg/dl or 1.3 mM

42
Q

levels of PO4 in children are (lower or higher). why?>

A

higher, due to active bone growth!!

43
Q

Describe the distribution of PO4 in the body

A

Bone (85%) > ICF (14%) > ECF <(0.1%)

44
Q

Describe the distribution of PO4 in the blood

A

Free (55%) > CATION bound (35%) > PROTEIN bound (10%)

**the ppt slide was wrong!!

45
Q

How is PO4 excreted

A

Urine > feces

*kidney clearance more imp for maintaining PO4 balance

46
Q

Describe the changes in PO4 metabolism with renal failure

A

↓renal Cx → ↑ Sr PO4 (→ ↑bone mineralization → ↓Ca → ↑PTH → ↑ VitD ??) → ↑bone resorption

+ deposition of Ca in vasculature

47
Q

FGF23 is produced in ____

A

bone

48
Q

FGF 23 is secreted into blood in response to …

A

↑PO4
↑ Vit D
↑ PTH

49
Q

FGF23 acts in kidneys to…

A

↓ expression of Na-PO4 co-transporter (↓reabs) and dec vitD synthesis
→ ↓PO4 (→ ↑bone resorption and ↑Ca)

Endo (28 decks)

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