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S&F 4 test 1 > McCumbee- Calcium Homeostasis > Flashcards

McCumbee- Calcium Homeostasis Flashcards

1
Q

Normal plasma concentration of calcium?

A

Between 8.5 and 10.5 mg/dl

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2
Q

___% of calcium is free ionized calcium, the biologically active form

A

50

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3
Q

What are the 3 principle organs involved in Ca and Phosphate homeostasis?

A

Small intestine

Skeleton

Kidneys

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4
Q

The principle regulators of calcium and phosphate homeostasis are _____ and _____

A

PTH

Vitamin D

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5
Q

What four things are associated with negative calcium balance (net calcium loss)?

A

Immobilization of a limb

Weightlessness in space

Prolonged bed rest

Certain forms of cancer

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6
Q

Positive calcium balance (net calcium gain) is associated with?

A

Skeletal growth

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7
Q

Type of bone

Makes up 80% total bone mass

Particularly strong because of a densely packed matrix

Shafts and ends of long bones

Surface of other bones

A

Cortical bones

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8
Q

Where is cortical bone found?

A

Shafts and ends of long bones

Surface of other bones

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9
Q

Made of interconnecting bone spicules

Contains 80% of bone surface, but 20% of bone mass

Insides of flat bones

Vertebral bodies

Epiphyses and interior of the diaphysis of long bones

A

Trabecular bones

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10
Q

Where are trabecular bone found (interconnecting bony spicules)

A

Inner portion of flat bones

Vertebral bodies

Epiphyses and interior of the diaphysis of long bones

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11
Q

Remodeling of bones is essential for?

A

Maintaining structural integrity of skeleton

Supporting mineral homeostasis

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12
Q

Which type of bone has the highest yearly remodeling rate?

A

Trabecular bone (20% per year)

[cortical bone remodels at a rate of 4% per year]

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13
Q

This system is the primary mechanism thru which osteoblasts and osteoblast lineage cells regulate osteoclastogenesis and bone remodeling

A

OPG/RANK-L/RANK system

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14
Q

RANK-L expression is ______ by PTH and Vitamin D

A

Stimulated

(RANK-L is the surface ligand on osteoblast lineage cells that tell the osteoclast precursors, which have RANK receptors, where to bind)

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15
Q

RANK-L expression is stimulated by _____ and ______

A

PTH

Vitamin D

(RANK-L is the surface ligand on osteoblast lineage cells that is where the osteoclast precursor cells are able to bind with their RANK receptors)

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16
Q

RANK-L expression is _______ by estradiol.

A

Inhibited

(RANK-L is the surface ligand on osteoblast lineage cells that tell the osteoclast precursors, which have RANK receptors, where to bind)

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17
Q

RANK-L expression is inhibited by ______ .

A

Estradiol

(RANK-L is the surface ligand on osteoblast lineage cells that tell the osteoclast precursors, which have RANK receptors, where to bind)

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18
Q

_________ are able to release OPG (osteoprotegerin), which is a soluble protein that binds RANK-L and prevents it from activating RANK

A

Osteoblasts and osteoblast lineage cells

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19
Q

________ inhibits RANK-L induced differentiation of proteoclasts when necessary by preventing it to activate RANK in osteoclasts and preosteoclasts.

A

OPG

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20
Q

OPG production is stimulated by ________

A

Estradiol

It is inhibited by PTH

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21
Q

OPG production is inhibited by ________

A

PTH

It is stimulated by estradiol

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22
Q

What does M-CSF do?

Macrophage colony stimulating factor

A

Promotes the early differentiation of monocyte/macrophage lineage cells and works with RANK-L to PROMOTE osteoclastogenesis

M-CSF also bind receptors in osteoclast precursors causing them to proliferate and enhancing their survival

(Resorption)

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23
Q

Where is M-CSF secreted from?

A

Osteoblast lineage cells

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24
Q

Osteoprotegin ________ the activity of the RANK-Ligand system

A

Antagonizes

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25
Q

The osteoclast’s ruffled edge, which forms after sealing zone attaches, releases H+ by ?

A

H+ ATPase

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26
Q

What are the two things that bound osteoclasts secrete to degrade the bone?

A

H+ to dissolve the hydroxyapatite crystal

Proteases to digest the matrix protein

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27
Q

What are some bone turnover markers (products of osteoclast mediated bone resorption) that are used to evaluate bone turnover clinically?

A

Fasting urine calcium

Serum/urine CTX (C-terminal telopeptides of Type 1 collagen)

NTX (N-terminal telopeptide of type 1 collagen)

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28
Q

What is the fate of osteoblasts following matrix formation?

A

Become lining cells

Differentiate into osteocytes

Undergo apoptosis

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29
Q

Principal bone crystal

A

Hydroxyapatite

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30
Q

How does vitamin D increase Ca absorption?

A

At genomic level; increases synthesis of calbindin and TRPV6 [calcium transport protein]

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31
Q

Explain the transcellular intestinal absorption of calcium (this is most active when dietary calcium levels are low)

A

Ca+ enters enterocyte thru TRPV6 channel. Ca is then bound by calbindin (keeps Ca gradient low and protects cell from harm of high Ca). Calcium is then carried to basolateral membrane where it leaves cell to bloodstream thru either calcium ATPase or a Ca-Na antiporter.

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32
Q

Vitamin D3 ________ Npt2b channel synthesis when dietary phosphate levels are low

A

Increases

33
Q

Explain phosphate absorption in intestinal cells

A

There are paracellular and transcellular routes

Transcellular; PO4 enters cell thru Nptb2 channel (this is a Na-Phosphate cotransporter [IC Na levels kept low by Na/K atpase])

34
Q

_______ is able to make minute to minute homeostatic adjustments in blood calcium and blood phosphate concentrations

A

PTH

This is done by altering PTH-sensitive transporters in the nephron

35
Q

PTH affects TRPV5 (calcium channel in kidney) by ?

X3

A

Direct phosphorylation

Inducing its transcription

Inhibiting its removal from apical surface of distal convoluted tubule

[this all helps PTH make minute to minute adjustments in blood calcium concentration]

36
Q

About __-% of calcium in the glomerular filtrate is reabsorbed by saturable active transport mechanism in the distal convoluted tubules.

This mechanism is regulated by PTH

A

9

37
Q

PTH ________ urinary phosphate excretion by inhibiting phosphate reabsorption and distal conv tubules (effect on proximal is most important)

A

Increases

38
Q

In the kidney, PTH induces the synthesis of ________ in the proximal tubules. This enzyme catalyzes the conversion of vitamin D to the most active form.

A

1a-renal hydroxylase

39
Q

What are the three main functions of PTH in the kidney

A
  1. Regulate Ca reabsorption
  2. Increase PO4 excretion
  3. Make 1-alpha-renal-hydroxylase which converts vitamin D to the most active form.
40
Q

PTH is secreted by _______ cells of the parathyroid

A

Chief cells

41
Q

_________ is a mechanism for controlling the amount of intact PTH released by chief cells

A

Intraglandular degradation

42
Q

Why do you want to get rid of phosphate (PTH regulated) when you’re resorbing calcium from bone.

A

Ca and PO4 can create a precipitate so you want to decrease the likelihood of that.

43
Q

the ______ terminal of intact PTH hormones is important in determining biological activity

A

N-terminal region

44
Q

Synthetic ____ terminals with 1-34 AA’s can induce ALL known actions of PTH.

A

N

45
Q

____________ is a way that the chief cells regulate the quantity of intact PTH that is released

A

Intraglandular degradation

46
Q

In order to regulate the amount of PTH released. Secretory granules with PTH have proteases that do what?

A

Degrade intact PTH to inactive C-terminal fragments

47
Q

In a state of hypercalcemia, what happens to the release of inactive C-terminal fragments of PTH

A

It increases

48
Q

In a state of hypocalcemia, what happens to the release of inactive C-terminal fragments of PTH?

A

It decreases

49
Q

The principal phsyiological regulator of PTH secretion is the concentration of ionic calcium in ______

A

ECF

(Chief cells of the parathyroid gland are very sensitives to changes in this)

[2-3% change from the normal [Ca] will elicit a significant response]

50
Q

In acute hypocalcemia, the chief cells of the parathyroid gland respond within minutes by releasing more pre-formed PTH. If hypocalcemia continues for days, what is the response?

A

Increase in PTH gene transcription and PTH mRNA stability increase

(If there is an even more prolonged period of hypocalcemia, there is an increase in the rate of chief cell proliferation)

51
Q

The basal rate of PTH secretion, which is about ___% of maximum rate, is unaffected by Ca levels in ECF.

A

5

52
Q

What are inhibitors of the parathyroid glands secretion of PTH (x2)

A

Vitamin D3 (active)

Calcium rise

53
Q

Active Vitamin D effects PTH secretion by?

A

Working on the genomic level to suppress PTH gene expression.

54
Q

What are the actions of type 1 PTH receptor when PTH or PTH-related protein bind to it

A

GCPR pathway to increase levels of cAMP

Turn on IP3/diacylglycerol pathway which will activate phospholipase C

55
Q

PTH ______ the expression of RANK-L

A

Promotes

56
Q

PTH _______ the expression of OPG

A

Down regulates

OPG is the soluble molecule that competes with RANK for RANK-L

57
Q

The effects of PTH on kidney function are responsible for ?

A

The minute-to-minute homeostatic adjustments of Ca levels in ECF

58
Q

What type of signs and symptoms are there of PTH-induced hypercalcemia

A

Non-specific (weakness, fatigue, loss of appetite, tiredness)

GI (V, pancreatitis, abd pn, constipation, Peptic ulcers {more gastrin})

Neuro: confusion, mild depression loss of concentration

Kidney stones —> decreased kidney function

Decreased membrane excitability

59
Q

Clinical features of hypoparathyroidism are due to hypocalcemia.

What are some of these symptoms.

A

Neuronal membranes are extra permeable and excitable.

Hypocalcemic tetany of hand and Traousseau’s sign of latent tetany

60
Q

What type of serum calcium levels are associated with tetany in the hand

A

Calcium at 6mg/dl

61
Q

What are the major causes of hypoparathyroidism

A

Surgery

Autoimmunity

62
Q

Rare familial disorder characterized by target tissue resistance to PTH

A

Pseudohypoparathyroidism

63
Q

_______ is the most common humoral cause of hypercalcemia in malignancy

A

PTHrP

64
Q

During fetal development, PTHrP regulates _______ flux thru the placenta from maternal to fetal circulation

A

Calcium

65
Q

form of vitamin D has very little biological activity and a long circulatory half-life.

It is the most abdundant form of vitamin D.

It is the predominant circulating form of vitamin D and thus what is measured clinically when assessing a patient’s vitamin D status.

A

25(OH)D

66
Q

Most potent vitamin D metabolite

Formation catalyzes by 1-alpha-hydroxylase in kidney

A

1,25(OH)2D

67
Q

What 2 things have an inhibitory effect on 1-alpha-hydroxylase

A

High plasma calcium

High levels of 1,25(OH)2D

68
Q

What are target tissues of vitamin D3 (x4)

A

Small intestine

Bone

Parathyroid glands

Kidneys

69
Q

More than 99% of the vitamin D and vitamin D metabolites in circulation are bound to plasma proteins. The principal carrier is an alpha-globulin called __________

A

Vitamin D binding protein (DBP)

In proximal tubules, the entire Vitamin D-DBP binding complex is taken up by receptor mediated endocytosis

70
Q

What does 1,25(OH2)D do in the intestinal epithelium?

A

Increases calcium absorption from the lumen.
By increasing expression of epithelial calcium channels
(Also increases expression of calbindin-D9k)

particularly dramatic response in the duodenum where vitamin D receptor concentration is the greatest

71
Q

Actions of vitamin D on bone?

A

Works synergistically with PTH to promote mobilization of calcium from bone

Indirect stimulatory effects on bone mineralization

72
Q

What are vitamin D’s affects on the parathyroid gland?

A

Negative feedback on PTH secretion by inhibiting expression of gene

Also modulates chief cell response to Ca and Vit D by inducing expression of CaSR and Vit D receptor

73
Q

What are VItamin D’s affect in bone?

A

Help w/ proper bone mineralization by making sure Ca and PO4 are there

Promote osteoclasotgenesis by inducing RANK-L expression on osteoblasts and by suppressing osteoprotegerin (OPG) synthesis

74
Q

How does Vitamin D affect the kidney?

A

It modulates its own formation by inhibitting 1-alpha-hydroxylase activity and stimulating 24-hydroxylase

75
Q

What are causes of vitamin D deficiency? (X4)

A

Malabsorption

Nadequate sun exposure

Defect in activation enzymes

Defect in vitamin D receptor

76
Q

What is a consequence of Vit D deficiency?

A

Decreased bone mineralization

Rickets/osteomalacia

77
Q

How does calcitonin work? (Calcitonin is not a major regulator of calcium homeostasis in humans)

A

Released in response to gastrin or high Ca levels.

Suppresses bone resoprtion by cAMP-dependent mechanism

Osteoclasts have receptors

78
Q

What is a clinical use for calcitonin?

A

Treatment of osteoporosis

79
Q

What do CaSR (calcium sensing receptors) do in chief cells of parathyroid?

A

Monitor minute to minute changes in calcium. In stages of high calcium, cause activation of phospholipase A2, increase arachadonic acid, increase leukotrienes which leads to the intraglandular degradation of PTH.

In absence of Calcium, these receptors stimulate PTH release

S&F 4 test 1 (22 decks)

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