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MED 310 > parathyroid and calcium regulation > Flashcards

parathyroid and calcium regulation Flashcards

1
Q

what is calcium homeostasis essential for

A

bones and teeth

all cells

nerve and muscle function

blood clotting

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2
Q

what are the three hormones responsible for calcium homeostasis

A

patathyroid hormone PTH
calcitonin
vitamin D

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3
Q

what percentage of bone and teeth is calcium

A

99

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4
Q

what percentage of soft tissue cells is calcium

A

0.9

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5
Q

what percentage of ECF is calcium

A

0.1

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6
Q

what is the ECF broken into and the calcium percentage

A

0.05 protein bound or inorganic complexes
0.05 free ionized

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7
Q

what kind of calcium is bioactive

A

only free ionized Ca2+

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8
Q

what parts of calcium cocentration are regulated

A

both ECF plasma conc of ionized calcium and total body calcium

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9
Q

what is 0.05 free ca in ECF regulated by

A

exchange bw bone and ECF
renal excretion

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10
Q

what kind of regulation is ECF free ionized ca regulation

A

min to min regulation

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11
Q

how is total body calcium regulated

A

by GI absorption of ca
renal excretion

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12
Q

what kind of regulation is total body ca regulation

A

long term regulation

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13
Q

what are the two types of cells of the parathyroid gland

A

cheif cells
oxyphil cells

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14
Q

what do chief cells have

A

calcium ion sensing receptor

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15
Q

what kind of hormone is PTH

A

peptide hormone

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16
Q

what kind of feedback loop is PTH regulated by

A

negative feedback

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17
Q

negative feedback of PTH

A

PTH synth and secretion stiumulated by low plasma ionized Ca

PTH raises free ionized Ca in ECF

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18
Q

what does PTH act on

A

bone, kidney, and

GI tract- via vit D

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18
Q

what does PTH act on

A

bone, kidney, and

GI tract- via vit D

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19
Q

how long does it take for complete skeletal turnover

A

every 10 yrs

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20
Q

what do osteoblasts do

A

create new bone by secreting organic matrix- osteoid and then mineralizing it with calcium crystals

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21
Q

what do osteocytes do

A

involved in calcium regulation but do not create new bone

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22
Q

where do osteocytes arise from

A

entombed osteoblasts

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23
Q

what do osteoclasts do

A

dissolve bone- bone resoption by solubilizing the crystals

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24
Q

what does PTH stimulate

A

movement of ionized Ca from bone fluid to ECF- fast response time

bone dissolving activity of osteoclasts- slower response time- coincident release of ca and phosphate

PTH tips bone remodeling in favour of resorption

25
Q

PTH fast exchange effect to inc ca method

A

ca is moved from the labile pool in the bone fluid to the plasma by PTH activated Ca pumps located in the osteocytic-osteoclastic bone membrane

26
Q

PTH slow exchange effect to inc ca method

A

ca is moved from the stable pool in the mineralized bone to the plasma through PTH induced dissolution of bone by osteoclasts

27
Q

what is the osteocytic-osteoblastic bone membrane formed by

A

filmy s=cytoplasmic extension of interconnected osteocytes and osteoblasts

28
Q

where is the bone fluid labile pool of ca

A

in canailculi

29
Q

where is the ca in the plasma

A

in central canal

30
Q

what controls osteoclast activity

A

osteoblast derived factors

31
Q

PTH effect on kidneys

A

PTH inc renal reabsorption of ca and inc excretion of phosphate

PTH induces activation of vit D

32
Q

what effects does calcitonin have on bone remodelling compared to PTH

A

opposite

33
Q

what kind of hormone is calcitonin

A

peptide hormone

34
Q

what does calcitonin do

A

decreases movement of ionized calcium from bone fluid to ECF

inhibits activity of osteoclasts and therefore derceases bone reserption

inrceases renal calcium excretion

35
Q

what does the inverse regulation of PTH and calcitonin release act through

A

the same calcium sensing receptor mechanism

36
Q

what is the bioactive form of vitamin D

A

1,25 (OH)2 vitamin D3–calcitriol

37
Q

what is calcitriol derived from

A

inactive vitamin D produced in skin by action of sunlight or present in some food

38
Q

what is the biologically inactive precurson of vitamin D3 called

A

7- dehydrocholesteorl

39
Q

what kind of hormone is vitamin D

A

steroid hormone

40
Q

how is vitamin D activated

A

by addition of 2 hydroxyl groups

41
Q

how is vitamin D activated

A

by addition of 2 hydroxyl groups

1st added in liver- 25 OH vitamin D

2nd added in kidneys 1,25 OH2 vitamin D3

42
Q

what is the kidney hydroxylation enzyme stimulated by

A

PTH
low plasma ionized calcium
low plasma ionized phosphate
prolactin during lactation

43
Q

what happens when plasma ionized calcium is high

A

renal hydroxylation produces an inactive form
24,25 OH2 Vit D3 by a different enzyme

44
Q

what are the effects of activated vitamin D3

A

inc total body ca by inc GI ABSORPTION OF cA
-this is a dose dependant response
-slow long lasting response
-adjts ca intake from the diet to match needs via changes of ration activation./ inactive vit D

increases ECF ionized calcium by enhancing response of bone to PTH- resoption

45
Q

problems of calcium homeostasis

A

-hyperparathyriodism
-hypoparathyroidism
-vid D deficiency
-osteoporosis

46
Q

hypoparathydoism

A

rare condition usually caused by automimmune disease of physical damage to the glands

low PTH secretion results in low plasma ionied calcium level

causes increased neuromuscular excitability by increasing nrve membrane permeability to Na
-paresthesia- pins and needles
-tetany- muscle spasms
-potentially lethal due to failure of respiration

47
Q

what is the primary form of hyperthyroidism due to

A

usually due to hypersecreting patathyroid tumor

  • hypercalcemia results from high PTH
48
Q

what is hyperparathyroidism due to

A

chronic renal disease or vitamin D deficiency causing hypocalcemia which causes high PTH production

49
Q

hyperparathyroidism- high PTH level with elevated Ca causes

A

depressed muscel and nerve excitability
-high ECF ca conc

inc risk of fractures
-demineralization of bone

risk of kidney stones
-high conc of calcium in renal filtrate

50
Q

hyperparathyroidism with vid D deficiency what does it do

A

impairs Fi absorption of Ca

resulting high PTH causes bone demineralization
-in children- rickets
-in adults- osteomalacia

51
Q

how is rickets treated

A

vitamin D therapy

52
Q

what affects vitamin D production

A

skin pigmentation

african- dark skin tone is 100% deficient

53
Q

what are the heath risks of vit d deficiency

A

elevated risk of cancer, cardiovascular disease, autoimmune disease, multiple sclerosis, osteoporosis

54
Q

what lowers risk of premature death

A

vitamin d supplements

55
Q

where are vitamin D3 receptors expressed

A

everywhere in the body

56
Q

osteoporosis

A

condition in which bone resorption is greater then bone formation
-reduced osteoblast activity incrased osteoclast activity
-plasma calcium, phosphate PTH, and vitamin D levlels are usually normal

-reuslts in reduction of bone mass

57
Q

what decreases with aging

A

bone density and bone mass

58
Q

what inhibits bone resorption and how does it do it

A

estrogen by deceasing osteoclasts activity and increasing osteoblast activity

59
Q

when is there increased incidence of osteoporosis

A

post menopausal women when estrogen levels are reduced

60
Q

what does prevention of osteoporosis include

A

adequate calcium and vid D throughout life

doing weight bearing exercise

not smoking

MED 310 (47 decks)

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