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unit 6: physiology > parathyroid hormone (12) > Flashcards

parathyroid hormone (12) Flashcards

1
Q

what is the total amount of calcium in the body? (in mg/dL)

A

9-10.6 mg/dL

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2
Q

in mg/dL what is amount of ionized calcium in the body?

A

4.05-5.2 mg/dL

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3
Q

what calcium value is typically measured in blood tests?

A

total calcium

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4
Q

what are the two forms of calcium found in the blood?

A

protein bound- 40%

ultra filtrable- 60%

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5
Q

what two groups can the “ultafilterable” be broken into?

A

complexed to anions- 10%

ionized calcium 50%

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6
Q

what percentage of calcium in the body is in the ECF and muscles?

A

only 1% !!

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7
Q

what percentage of calcium in the body resides in the plasma (extracellularly)?

A

.1%!! and half of that is ionized

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8
Q

if a person has a higher than normal albumin level, how can this affect measuring their calcium levels?

A

it can cause a high calcium which would be a false positive when in reality ionized calcium can be totally normal (and this is what you really care about)

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9
Q

what effects can acidemia have on ionized calcium?

A

it can cause albumen in the plasma to bind LESS calcium leading to a TRUE increase in ionized calcium

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10
Q

what are some symptoms of hypercalcemia? what value in mg/dL is considered hypercalcemia?

A

> 12 mg/dL
fatigue, apathy, anorexia, delirium, coma, headache, increase intracranial pressure,
high calcium concentration will increase membrane polarization and reduce neural response

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11
Q

what are some symptoms of hypocalcemia? what value in mg/dL is considered hypocalcemia?

A

<7mg/dL
leading retardation, apnea (children
tetany, numbness, muscle cramps
low calcium concentration will reduce the membrane polarization and increase hypersensitivity

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12
Q

what 3 organ systems are involved in maintaining a normal “calcium economy”

A

digestive system
kidneys
bone

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13
Q

what percentage of our ingested calcium in excreted in the feces?

A

80%

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14
Q

what role does the kidney play in calcium balance?

A

filters 10x the average daily intake and recaptures almost all of it (175mg/day is excreted in urine)

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15
Q

what is the turnover of bone in adults per day?

A

280 mg/day

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16
Q

what two key hormones control calcium homeostasis?

A

vit D and PTH

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17
Q

what will be the effect of binding of PO4 to calcium?

A

it will reduce the ionized calcium level

it tends to “buffer” the calcium concentration

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18
Q

what gland produces calcitonin?

A

thyroid gland

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19
Q

what is the function of calcitonin?

A

inhibits bone resorption

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20
Q

describe the effects of PTH on the kidney

A

rapid effects

  • increases calcium by increasing re-abosorption in the distal tubule
  • decrease PO4 by reducing re-absorption in the proximal tubules
  • increase 1,25 (OH) D3 synthesis
  • increase urinary cAMP
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21
Q

what is the effects of PTH on the bone cells?

A

increase osteoCLASTIC resorption via receptors on the osteoblasts–>this increase calcium and PO4 in the ECF and plasma

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22
Q

what cells secrete RANK-L?

A

osteoblasts

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23
Q

what is the effect of RANK-L on monocyte lineage cells?

A

causes their maturation into active multinucleated osteoclasts

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24
Q

what cells release PTH?

A

chief cells of the parathyroid gland

25
Q

how does low calcium trigger the release of PTH?

A

calcium sensing receptor is a G protein coupled receptor with a signaling cascade involving intraceullar calcium binding/releasing from the ER

26
Q

what is familial hypercalcemic hypocalcuria (HFF)?

A

caused by mutation in the calcium sensing receptor gene
there is increase tubular re-absorption of calcium
these ppl’s “normal calcium” levels will be high but they will not have symptoms

27
Q

what percentage of daily calcium is re-absorbed at the proximal tubule? distal tubule? what about the rest?

A

proximal tubule- 60%
distal tubule- 9%
the rest of the calcium is re-absorbed via passive diffusion in most other locations

28
Q

what part of the kidney does PTH act to increase ca++ re-absorption?

A

distal tubule

29
Q

what are the 4 targets of vitamin D?

A

intestine
bone
parathyroid gland
kidney

30
Q

what are the effects of vit D on PTH?

A

tends to reduce PTH production in the parathyroid gland

does this to act as a buffer to make sure correcting the low calcium doesn’t get out of control

31
Q

what is a marker for bone turnover that can be seen in a parathyroid adenoma?

A

alkaline phosphatase

32
Q

What is the cause of high serum calcium in Humoral Hypercalcemia Malignancy?

A

The release of PTH- related peptide by tumors. THe PTH-rp activates the same receptors as PTH, which causes serum Ca++ to increase

33
Q

What is the cause of secondary hyperparathyroidism?

A

Hypocalcemia is primary cause (due to low vit D, renal failure, diet)

34
Q

What is psuedohypoparathyroidism?

A

Hypocalcemia due to a genetic defect in the G protein in PTH receptor in kidney

35
Q

What is the cause of Familial hypocalciuric hypercalcemia?

A

genetic defect in Ca++ sensors, which increases Ca++ reabsorption

36
Q

Normal plasma range of Phosphorus? How much is bound to protein?

A

2.5-4.5 mg/dL. 10-20% is bound to protein.

37
Q

What cells line the bone surfaces and actively synthesize bone?

A

OsteoBlasts

38
Q

Describe how collagen is matured?

A

Precursor molecules of collagen are synthesized in the cell and exported attached as telopeptides. Outside the cell the collagen molecules further polyerize in a crystalline arrangement to forms long fibrils.

39
Q

What is found between the layer of osteoBlasts and the mineralizing matrix?

A

Osteoid, this is not yet mineralized collagen

40
Q

What is the osteoid a indication for?

A

The state of health of the skeleton and the availability of Ca and PO4

41
Q

Which cells do most of the signalling in the bone?

A

OsteoBlasts

42
Q

What do osteoblasts have receptors for?

A

PTH, Vit D, Estrogen, many paracrine factors and growth factors

43
Q

What comprises the weight of the bone?

A

Bone Mineral 65%

Collagen 22%

Fluid 10%

Non-collagenous proteins and cells 1-2%

44
Q

How does bone mineralization begin?

A

Microcrystalline HA mineral deposition in collagen matrix. Crystals begin to form in “hole” regions.

45
Q

What are the two methods of bone remodeling?

A

1- Osteonal Tunneling

2- Surface Remodeling

46
Q

Describe osteonal tunneling?

A

Occurs in cortical bone, osteoclasts drill through the bone and osteoblasts follow and lay down bone. Haversian canals result from this action.

47
Q

Describe Surface remodeling?

A

Occurs in trabecular bones. Osteoclasts breakdown bone and steoblasts replace and new bone forms. This liberates a lot of Ca++ and PO4.

48
Q

What allows for osteoclats to mature an be activated?

A

A cytokine from the osteoblast lineage cells called RANK-L

49
Q

What does RANK-L bind to?

A

RANKs (on osteoclasts and precursor cells)

50
Q

What competitively inhibits RANK-L?

A

OPG which is a soluble substance produced by osteoBlasts

51
Q

What are the effects of estrogen on bone remodeling?

A

Reduces reabsorption

52
Q

What are the effects of calcitonin on bone remodeling?

A

Transient inhibitor of osteoclasts

53
Q

Do glucocorticoids inhibit or enhance intestinal Ca absorption?

A

Inhibits

54
Q

How does mechanical loading effect bone remodeling?

A

Locally promotes cone accrual and maintenance

55
Q

What are the elements of the bone that are most sensitive to mechanical loading? What is the action of these elements?

A

Osteocyte and its connected canaliculae work to reduce the expression of sclerostin

56
Q

What is sclerostin?

A

An inhibitor of bone formation mediator when bone loading is weak.

57
Q

What is osteoporosis?

A

Related to disease or aging…it is inappropriate or excessive remodeling

58
Q

What is osteopenia?

A

Substantial bone loss but not enough to be in danger of fracture.

unit 6: physiology (13 decks)

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