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IHN: Biochemistry 2 > calcium > Flashcards

calcium Flashcards

1
Q

bioavailability of caclium is affected by

A

dense food matrix

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2
Q

high bioavailability
low bioavailability

A

high bioavailability = dairy
low bioavailability = green-leafy vegetables

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3
Q

factors that reduce bioavailability of calcium

A
  1. dietary fiber
  2. phytic acid
  3. oxalate
  4. divalent cations (Zn, Cu)
  5. unabsorbed fatty acids (FFA)
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4
Q

calcium must be in __/__ form to be absorbed

A

calcium must be in ionic/free form to be absorbed (Ca2+)

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5
Q

__ pH facilitates formation of __ calcium

A

low pH facilitates formation of ionic calcium

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6
Q

fractional Ca2+ absorption is percent of Ca2+ absorbed by __ from __ Ca2+

A

fractional Ca2+ absorption is percent of Ca2+ absorbed by intestine from oral load Ca2+

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7
Q

young adults fractional Ca2+ absorption

A

25-30%

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8
Q

fractional Ca2+ absorption decrease with __ and increases with __

A

fractional Ca2+ absorption decrease with age and increases with 1st trimester of pregnancy

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9
Q

2 methods of calcium absorption

A
  1. transcellular, carrier-mediated transport process (saturable)
  2. paracellular, passive diffusion process
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10
Q

calcium absorption is mediated by

A

calcium absorption is mediated by vit D

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11
Q

vit D induces expression of (4)

A
  1. TRPV6
  2. Calbindin
  3. PMCA1b
  4. NCX1
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12
Q

transcellular, carrier mediated transport steps

A
  1. TRPV6 moves Ca2+ into cytosol of enterocyte
  2. Calbinidin D9K binds absorbed Ca2+ and transports it to basolateral membrane
  3. PMCA1b (Ca2+ dependent ATPase) pushes Ca2+ into portal circulation
  4. Calbindin brings Ca2+ to NCX1 (Na+, Ca2+ exchanger), pushes 1 Ca2+ out and one Na+ in
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13
Q

paracellular, passive diffusion

A

Ca2+ cross epithelial barrier btwn cells due to presence of occludins, paracellin-1, and claudins (creates a tunnel for Ca2+

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14
Q

vit D induces expression of

A

paracellin-1

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15
Q

50% of Ca2+ in systemic and portal circulation is bound to
the rest is

A

albumin or pre-albumin
the rest is free

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16
Q

do pregnant women need more Ca2+

A

yes

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17
Q

upper limit __ as we age

A

upper limit decreases as we age

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18
Q

__% of calcium filtrated in the kidney is reabsorbed

A

98% of calcium filtrated in the kidney is reabsorbed

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19
Q

__ is responsible for 90% of reabsorption

A

passive diffusion is responsible for 90% of reabsorption

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20
Q

reabsorption in kidney occurs in
70%
20%

A

reabsorption in kidney occurs in
70%: proximal tube
20%: ascending loop of Henle

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21
Q

remaining 10% of calcium is reabsorbed via __

A

remaining 10% of calcium is reabsorbed via active transport

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22
Q

which method of calcium reabsorption is more important?

A

10% via active transport
bc it ensures calcium absorption during scarcity

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23
Q

resorption of calcium in the kidney

A
  1. TRPV5 absorbs Ca2+ into renal epithelial cells
  2. Calbindin D28K binds reabsorbed Ca2+ and transports it to basolateral membrane
  3. PMCA1b and NCX1 push Ca2+ into blood
  4. Paracellin-1 allows Ca2+ to passively diffuse from urine to blood
24
Q

only __% of filtered Ca2+ is excreted

A

only 1-2.5% of filtered Ca2+ is excreted

25
Q

pregnant and lactating women reabsorb __ calcium bc calcium reabsorption is regulated by __ and __

A

pregnant and lactating women reabsorb more calcium bc calcium reabsorption is regulated by vit D and estrogens

26
Q

__ allows passive diffusion of Ca2+ from __ to __

A

Paracellin-1 allows passive diffusion of Ca2+ from urine to blood

27
Q

2 physiological roles of calcium

A
  1. structural function
  2. protein activation
28
Q

calcium in structural function

A

hydroxapatite and calcium carbonates in bones

29
Q

protein activation by calcium (2)

A
  1. direct (annexing, blood clotting enzymes, phospholipase A2)
  2. mediated by Ca2+ as a second messenger (calmodulins, calpains, protein kinase C)
30
Q

calcium signaling mechanism

A
  1. stimulus binds receptor
  2. activates G-protein cascade, activates phospholipase C (PLC)
  3. PLC converts phospolipid to inositol-P3 (InsP3)
  4. InsP3 targets ER or SR (organelles that sequester calcium)
  5. InsP3 binds ryanodine receptor (RyR)
  6. Ca2+ binds cytoplasmic calmodulin upon release from ER and SR
  7. active calmodulin targets Ca2+ sensitive kinases
  8. Ca2+ is extruded by Na/Ca exchanger or PMCA
31
Q

2 methods of Ca2+ extrustion from cell

A
  1. Na/Ca exchanger (secondary active)
  2. PMCA (active transport)
32
Q

skeleton contains __% of calcium

A

skeleton contains 99% of calcium

33
Q

calcium plays a huge role in makeup of

A

bones and teeth

34
Q

hormones that regulate calcium and phosphate

A

PTH
vit D
calcitonin

35
Q

PTH is secreted when Ca2+ levels are

A

PTH is secreted when Ca2+ levels are low

36
Q

PTH target tissues (3)

A

kidney
bone
intestine

37
Q

in kidney, PTH effects
PTH induces increased __ reabsorption and decreased __ reabsorption
PTH induces production of active vit D which increases intestinal absorption of __

A

in kidney, PTH effects
PTH induces increased Ca2+ reabsorption and decreased PO4 3- reabsorption
PTH induces production of active vit D which increases intestinal absorption of BOTH Ca2+ and PO4 3-

38
Q

PTH induces bone resorption to __ circulating Ca2+ levels

A

PTH induces bone resorption to increase circulating Ca2+ levels

39
Q

PTH action on intestine relies on

40
Q

bone remodeling cycle

A
  1. PTH induces resorption: osteoclasts dig into bone, release Ca and phosphorous
  2. reversal: mononuclear cells occupy the depression
  3. monnuclear cells recruit pre-osteoblasts to occupy depression
  4. bone formation: osteoblasts release collagen, Ca2+, PO4 3- to form new bone (mineralization)
  5. minerlization: new osteoblasts are buried in crystal structure and become osteocytes
41
Q

RANKL-RANK-OPG pathway controls

A

bone resorption

42
Q

in RANKL-RANK-OPG, PTH is catabolic/anabolic

A

PTH is catabolic/anabolic

43
Q

__ direct/drive bone resorption (breakdown), but __ do the actual activity of resorption

A

osteoblasts direct/drive bone resorption (breakdown), but osteoclasts do the actual activity of resorption

44
Q

OPG-RANKL-RANK pathway

A
  1. growth factors, PTH, cytokines induce osteoblasts to produce M-CSF, RANK ligand (RANKL) and OPG
  2. when enough M-CSF binds pre-osteoclast receptors, osteoclast matures
  3. RANKL binds RANK on mature osteoclast, osteoclast differentiates and is activated
  4. osteoclasts produce HCL and cathespins which resorb bone and release Ca2+ and PO4 3-
  5. osteoblasts release OPG which binds RANKL and prevents it from activating RANK receptors (prevents excess bone resorption)
45
Q

osteoblasts release __ which binds RANKL and prevents it from activating __ to prevent excess bone resorption

A

osteoblasts release OPG which binds RANKL and prevents it from activating RANK to prevent excess bone resorption

46
Q

estrogen promotes __ which __ bone resorption

A

estrogen promotes OPG expression which reduces bone resorption

47
Q

PTH is both

A

anabolic (bone formation) and
catabolic (bone resorption)

48
Q

PTH is both

A

anabolic (bone formation) and
catabolic (bone resorption)

49
Q

PTH stimulates osteoblasts to release __, which triggers bone resorption by allowing __ to be released into bloodstream

A

PTH stimulates osteoblasts to release RANKL, which triggers bone resorption by allowing Ca2+ to be released into bloodstream

50
Q

what hormone corrects calcium deficiency

51
Q

the __ and __ of PTH exposure deermine net effect on bone mass (cata or ana)

A

the duration and periodicity of PTH exposure deermine net effect on bone mass (cata or ana)

52
Q

continuous exposure to PTH = __ effects seen in __ of bone remodeling cycle

A

continuous exposure to PTH = catabolic effects seen in first 3 weeks of bone remodeling cycle

53
Q

intermittent, low doses of PTH = __ effects seen in __ of bone remodeling cycle

A

intermittent, low doses of PTH = anabolic effects seen in last 3 months of bone remodeling cycle

54
Q

factors causing low bone mineral density

A
  1. low calium and vit D
  2. unhealthy lifestyle
  3. inadequate dietary protein levels
55
Q

is calcium deficiency common?

A

no, bc we have large reserves in our body

56
Q

chronic inadequate calcium intake causes

A

rickets
osteoporosis

IHN: Biochemistry 2 (38 decks)

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