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Biochem > Lecture 47- Calcium and Phosphate Homeostasis Part 2 > Flashcards

Lecture 47- Calcium and Phosphate Homeostasis Part 2 Flashcards

1
Q

how does chronic kidney disease affects calcium and phosphate homeostasis

A

impaired kidney function interferes with calcium and phosphate reabsorption

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2
Q

what is hypocalcemia defined as

A

total serum calcium concentration less than 8.5 mg/dL in the presence of normal plasma protein concentrations or a serum ionized calcium concentration less than 4.4 mg/dL

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3
Q

what are the symptoms of hypocalcemia

A

muscle cramping
increased neuromuscular excitability
muscle spasms
fatigue
cardiac dysfunction
depression, psychosis, seizures

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4
Q

what are causes of hypocalcema

A

-inadequate PTH production (hypoparathyroidism)
- PTH resistant
- inadequate vitamin D
- vitamin D resistance or sythesis defects

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5
Q

what is hypoparathyroidism

A

hypocalcemia with serum PTH inappropriately low for hypocalcemia state

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6
Q

what syndrome is most commonly associated with hypoparathyroidism

A

DiGeorge syndrome

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7
Q

what is the most common cause of hypoparathyroidism

A

autoimmune destruction of parathyroids/loss of parathyroids due to thyroidectomy

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8
Q

what happens in DiGeorge syndrom

A

congenital disease with complete lack of parathyroids at birth

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9
Q

what is the conventional treatment for hypoparathyroidism

A

mainly calcium and calcitriol supplementation

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10
Q

what do constitutively activating mutations in CaSR cause

A

autosomal dominant hypocalcemia

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11
Q

what happens in a constitutively activating mutation in CaSR

A

CaSR signals constitutively even though Ca2+ levels are low -> parathyroid misreads Ca2+ levels as high and inappropriately suppresses PTH

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12
Q

what is pseudohypoparathyroidism

A

hypocalcemia due to lack of responsiveness of target tissues to PTH

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13
Q

what is the level of serum PTH in pseduohypoparathyroidism and why

A

high because parathyroid gland keeps trying to respond to correct the low serum calcium

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14
Q

what is mutated in pseudohypoparathyroidism

A

mutations in G proteins in PTH signaling

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15
Q

which is a more common cause of hypocalcemia: vitamin D deficiency or hypoparathyroidism

A

vitamin D deficiency

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16
Q

how does the lack of vitamin D inhibit calcium and phosphate uptake in gut

A

downregulation of calcium and phosphate transport proteins, calbindins, TRPV6, NaPi-2b

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17
Q

what does vitamin D deficiency lead to in children? adults?

A

-children: rickets
-adults: osteomalacia

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18
Q

what type of disorder is VDDR type 1

A

autosomal recessive

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19
Q

what is the defect in VDDR type 1

A

renal 25-OH-vitmain D-1 alpha hydroxylase

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20
Q

what are the concentrations of Calcium, phosphate, PTH, and 1,25(OH)2D3 in VDDR1

A

calcium: low
phosphate: low
PTH: high
1,25(OH)2D3: very low

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21
Q

what type of disorder is VDDR type 2

A

autosomal recessive

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22
Q

what is the defect in VDDR type 2

A

vitamin D receptor

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23
Q

what are the concentrations of calcium, phosphate, PTH, and 1,25 (OH)2D3 in VDDR2

A

calcium: low
Phospahte: low
PTH: high
1,25(OH)2D3 : elevated

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24
Q

which form of VDDR has alopecia associated

A

type 2

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25
Q

what is hypercalcemia defined by

A

serum total calcium greater than 10.5 mg/dL or ionized calcium greater than 5.4 mg/dL

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26
Q

what are the symptoms of hypercalcemia

A

-fatigue
- electrocardiogram abnormalities
-nausea, vomitting, constipation
-anorexia
-abdominal pain
-hypercalciuria/kidney stone formation
-calcification of soft tissues
- hypercalcemia crisis occurs at greater the 2.5 ionized serum calcium

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27
Q

what are the causes of elevated PTH levels

A

-primary hyperparathyroidism
-familial hyperparathyroidism
- inactivating mutations of CaSR

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28
Q

what is the cause of elevated 1,25(OH)2D3

A

hypervitaminosis D

29
Q

what is hypercalcemia of malignancy

A

due to tumor production of factor which stimulate bone resorption

30
Q

how does severe dehydration cause hypercalcemia

A

will increase serum Calcium concentration without changing total blood calcium

31
Q

what happens in primary hyperparathyroidism

A

usually 1 of 4 parathyroid glands makes too much PTH due to development of benign adenoma resulting in excessive PTH synthesis/secretion

32
Q

what are the results of primary hyperparathyroidism

A

-hypercalcemia
- phosphate is low
-high bone turnover
-kidney stones

33
Q

what is the treatment for primary hyperparathyroidism

A

parathyroidectomy

34
Q

what is the familial primary hyperparathyroidism MEN1 due to

A

inactivation of tumor suppressor gene Menin

35
Q

what is familial primary hyperparathyroidism MEN2 due to

A

gain of function mutation in RET protoocnogene

36
Q

what do mutations in MEN result in

A

neoplastic tumors in several endocrine tissues including parathyroids

37
Q

what type of disorder is familial primary hyperparathyroidism MEN1? MEN2

A

MEN1: recessive
MEN2: autosomal dominant

38
Q

what will heterozygotes for inactive CaSR have

A

familial hypocalciuric hypercalcemia

39
Q

what happens in familial hypocalciuric hypercalcemia

A

CaSR doesnt signal even though Ca2+ levels are high and PTH is inappropriately elevated. Pi is lower than normal

40
Q

what do homozygotes for inactive CaSR have

A

neonatal severe hyperparathyroidism- potenitally fatal and requires parathyroidectomy

41
Q

what happens in hypercalcemia of malignancy

A

tumors secrete factors that stimulate bone resorption. some secrete PTHrP which mimics PTH actions leading to elevated serum calcium and bone degradation

42
Q

what is secondary hyperparathyroidism

A

oversecretion of PTH in response to conditions of hypocalcemia and or decreased 1,25(OH2)D3, can also be caused by vitmain D malabsorption

43
Q

what is the most common cause of secondary hyperparathyroidism

A

chronic renal failure

44
Q

what is hypophosphatemia defined by

A

phosphate levels lower than normal range, lower than 2.5-4.5 mg/dL

45
Q

what are the causes of hypophosphatemia

A

-decreased intestinal absorption of phosphate
-increased urinary excretion
-redistribution from extracellular fluid into cells/tissues

46
Q

what causes decreased intestinal absoprtion of phosphate

A

-dietary vitamin D deficiency/low sun exposure
- vitamin D receptor defects/synthetic defects
-malabsorption of vitamin D

47
Q

what is increased urinary secretion seen in

A

renal phosphate wasting disorders, primary and secondary hyperparathyroidism

48
Q

what phosphate disorders are rickets/osteomalacia associated with

A

hypophosphatemia

49
Q

what is the most common disorder of renal phosphate wasting

A

x-linked hypophosphatemic rickets

50
Q

what are the features of XLH

A

growth retardation, rachitic/osteomalacic bone disease, dental abscesses, weak bones

51
Q

what mutation is XLH due to

A

mutation in PHEX gene on X chromosome

52
Q

what is the mechanism of XLH

A

-PHEX produced by osteoblasts, osteocytes, odontoblasts
-PHEX normally inhibits FGF23 production
-XLH mutations of PHEX lead to inappropriately elevated FGF23 production even though serum phosphate is low- mainly by osteocytes
-FGF23 reduced renal absorption of phosphates

53
Q

what are the levels of Pi and 1,25(OH)2D3 in XLH

A

Pi is low
vitamin D is low

54
Q

what is the treatment form XLH

A

-phosphate supplementation/ high dose calcitriol
-maybe surgical intervention to correct limb deformities

55
Q

what is the mutation ADHR and what does it stand for

A

autosomal dominant hypophosphatemic rickets
- mutation in FGF23 that alters cleavage site so it cannot be proteolytically inactivated, FGF23 stays active longer

56
Q

what is the mutation in ARHR and what does it stand for

A

mutations in DMP1 which is expressed by osteocytes leading to overproduction of FGF23
- autosomal recessive hypophosphatemic rickets

57
Q

what is HHRH stand for and what is the mutation

A

hereditary hypophosphatemis rickets with hypercalciuria
-due to heterozygous or homozygous loss of function mutations in type 2 sodium phosphate cotransporter NaPi2c

58
Q

what is the level of 1,24(OH)2D3 in HHRH

A

elevated

59
Q

what is the treatment for HHRH

A

phosphate supplements alone

60
Q

what is the common theme of genes associated with inherited hypophosphatemic rickets/osteomalacia

A

they all result in elevated FGF23

61
Q

what is tumor induced osteomalacia (TIO)

A

acquired syndrome of renal phosphate wasting, factors secreted into circulation by tumors cause alternations in Pi metabolism that mimic hypophosphatemic rickets

62
Q

what is hyperphosphatemia defined by

A

phosphate levels greater than 4.5 mg/dL or higher than 1.5 mM

63
Q

what are the symptoms of acute hyperphosphatemia

A

-hypocalcemia
-suppresses 1 alpha hydroxylase activity in kidney lowering 1,25D3 levels, which further exacerbates hypocalcemia by reducing calcium uptake in gut/renal reabsorption

64
Q

what are the symptoms of chornic hyperphosphatemia

A

-soft tissue calcification, renal failure, secondary hyperparathyroidism, renal osteodystrophy
-hyperphosphatemia from renal failure plays role in development of secondary hyperparathyroidism

65
Q

what are the causes of hyperphsophatemia

A

-acute phosphate load
- decreased urinary excretion
-redistribution to extracellular space
-genetic causes of hyperphosphatemia (familial tumoral calcinosis)

66
Q

what is the cause of acute phosphate load

A

phosphate containing laxatives/enema

67
Q

what are the causes of decreased urinary excretion

A

renal insufficiency/failure
- secondary to hypoparathyroidism/pseudphypoparathyroisim
- vitamin D intoxiation

68
Q

what does the treatment of hyperphosphatemia involve

A

administration of phosphate binding salts-calcium, magnesium, aluminum
- aluminin avoided in patients with renal failure

69
Q

how do these diseases implicate dental care

A

-increased periodontitis in patients with hypophosphatemic rickets/osteomalacia
- some patients with vitamin D dependent ricks have thin enamel-> microscopic cracks harbor bacteria that cause cavities
- bisphosphonates cause BNJ
- poor muscle tone/muscle weakeness are common and seizures can occur

Biochem (34 decks)

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