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Joeli Unit 4 > Bone physiology > Flashcards

Bone physiology Flashcards

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1
Q

bone remodeling is regulated by

A

biochemical markers, mechanical activity, endocrine function

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2
Q

how long does the bone remodeling cycle take

A

~4-6 months

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3
Q

annual turnover is 4% for what type of bone

A

cortical bone

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4
Q

annual turnover is 25% for what type of bone

A

trabecular bone

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5
Q

between puberty and 3rd decade of life, bone density increases

A

~3% per year

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6
Q

bone loss rate after 30 years

A

0.3%-0.5% per year

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7
Q

bone loss rate after menopause

A

3% per year for 10 years (rapid loss)

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8
Q

bone loss rate >60 years

A

0.5%

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9
Q

vitamin D supplementation

A

800

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10
Q

calcium supplementation

A

total = 1200 (400-500 supplementation)

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11
Q

who has highest risk of fractures

A

white, thin females

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12
Q

overweight and risk of osteoporosis

A

decreased risk if overweight

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13
Q

phases of bone remodeling

A

Resorption
Reversal
Formation
Mineralization

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14
Q

how long is the resorption period

A

~10 days

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15
Q

osteoclasts are derived from

A

hematopoietic stem cells

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16
Q

osteoclasts resorb bone through secretion of

A

H+ and cathepsin K (digesting enzyme)

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17
Q

what are osteoclasts dependent on for maturation and differentiation

A

cytokines

MCSF
RANKL

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18
Q

MCSF bind to what cells

A

precursor cells –> pre osteoclasts

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19
Q

on what cell in RANK found

A

pre osteoclasts

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20
Q

RANKL binds to

A

RANK –> maturation and differentiation

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21
Q

a decoy receptor for RANKL

A

osteoprotegerin (OPG)

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22
Q

what stimulates OPG secretion

A

estrogen

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23
Q

OPG/RANK ratio is high

A

osteoclast apoptosis

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24
Q

OPG/RANK ratio is low

A

bone resorption

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25
Q

what do osteoblasts secrete

A

MCSF and RANKL

26
Q

what causes osteoblasts to secrete cytokines

A

PTH (parathyroid hormone)

27
Q

osteoblasts are derived from

A

mesenchymal precursor

28
Q

what promotes osteoblast maturation

A

growth factor released from RESORBED bone

29
Q

what specific growth factors promote maturation of osteoblasts

A

IGF1 and IGF2

30
Q

what do pre-osteoblasts secrete

A

bone morphogenic protein (BMP)

31
Q

BMP is important in

A

differentiation of mesenchymal cells

32
Q

what can a mature osteoblast become

A

lining cell, osteocyte, or can undergo apoptosis

33
Q

what causes PTH to be released into the blood

A

low calcium levels

34
Q

anabolic effects of PTH on bones

A

inhibits osteoclasts and activates osteoblasts

35
Q

anabolic effects of PTH on kidneys and intestines

A

encourage kidneys to get more calcium from the urine instead of excreting it
stimulate renal tubules to release calcitriol which works in the intestines to get more calcium

36
Q

calcitriol is also called

A

active vitamin D

37
Q

easy way to remember calcitriol

A

TRY all that you can to increase calcium levels

38
Q

anabolic effects of PTH

A

PTH given in low and intermittent doses can activate the WNT pathway which promotes osteoblasts and inhibits osteoclasts

39
Q

can PTH be used for osteoporosis treatment

A

yes – very specific usage. low and intermittent doses

40
Q

calcitriol (active vitamin D) is synthesized from

A

the kidneys

41
Q

what is secreted in response to PTH

A

calcitriol

42
Q

effects of calcitriol

A

increases osteocalcin production
stimulates maturation of osteoclasts
stabilizes systemic calcium levels by encouraging intestines to absorb more calcium

43
Q

what type of estrogen is necessary for bone health

A

bioavailable/free

44
Q

what percent of estrogen is free

A

2%

45
Q

what is bound estrogen bound to

A

sex hormone binding globulin

46
Q

effects of estrogen and bone health

A

reduces apoptosis of osteoclasts and osteoblasts
decreases oxidative stress
increases OPG
balances bone resorption with bone formation

47
Q

thyroid gland can release

A

thyroid hormones and calcitonin

48
Q

calcitonin is released in response to

A

high levels of circulating calcium

49
Q

effects of calcitonin on bones

A

stimulates osteoblasts
inhibits osteoclasts

50
Q

T3 effects on bone

A

increases osteoclast activity independent of osteoblast activity
stimulates bone resorption

51
Q

how does T3 affect the amount of bioavailable estrogen

A

induces more production of sex hormone binding globulin in the liver

52
Q

prolactin has what type of effects on bone remodeling

A

direct and indirect

53
Q

where are prolactin receptors located

A

on osteoblasts

54
Q

effects on prolactin receptors on osteoblasts

A

decrease osteocalcin mRNA
increased RANKL expression
decreased OPG expression

55
Q

indirect effects on prolactin

A

negative feedback to HPO axis –> increased PRL –> decreased estrogen –> increased bone resorption

56
Q

cortisol levels can be increased due to

A

stress
glucocorticoid meds

57
Q

effects of increased cortisol on intestines

A

decreased calcium absorption in intestines

58
Q

effects of increased cortisol on kidneys

A

increased renal excretion of calcium

59
Q

effects of cortisol on PTH

A

lowering calcium levels –> increased PTH

60
Q

effects of high cortisol on GnRH

A

decreased GnRH –> decreased estrogen –> imbalance of RANKL and OPG

61
Q

effects of cortisol on osteoclasts

A

increase osteoclast activity

62
Q

effects of cortisol on osteoblasts

A

decrease osteoblast activity

Joeli Unit 4 (6 decks)

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