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Protein-Bound vs. Free (Ionized) Calcium

Discussion in 'Step I' started by asaha, Apr 28, 2007.

  1. asaha

    asaha

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    Apr 28, 2007
    Hello,

    I understand that plasma calcium is found in both protein-bound and free (ionized) forms. Why does alkalosis increase the amount that is protein-bound?

    Thanks in advance!
     
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  3. UCLAstudent

    UCLAstudent I'm a luck dragon! 10+ Year Member

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    Calcium and H+ compete for some of the same protein binding spots. With a drop in H+ (alkalosis), this frees up some of the protein binding spots for calcium and leads to lower levels of free calcium.
     
  4. goodies

    goodies Member 7+ Year Member

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    patient hyperventilates and blows of Co2 --> respiratory alkalosis --> increased pH --> increased negative charges on albumin, increased binding of calcium to albumin without decrease in total ca++; decreased ionized calcium --> tetany

    it is due to a competition of sodium and calcium for channels in neurons. i don't think its with hydrogen
     
  5. blz

    blz Senior Member 10+ Year Member

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    UCLAstudent is right. Ca++ binds apartic and glutamic acid residues on albumin. these AAs are very sensitive to pH. A higher PH deprotonates them even more allowing greater binding of Ca.
     
  6. predodoc

    predodoc Junior Member 7+ Year Member

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    How many of you learned that from Goljan?
     
  7. doctorp82

    doctorp82 Palpating preschoolers 2+ Year Member

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    I learned it from Chvostek and Trousseau

    I wonder how cool you had to be to have two sign's named after you (Trousseau)?
     
  8. blz

    blz Senior Member 10+ Year Member

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    learned the ca stuff from class.


    speaking of signs, I think the Chandelier sign is the coolest. also, Courvoisier's sign just sounds badass.
     
  9. UCLAstudent

    UCLAstudent I'm a luck dragon! 10+ Year Member

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    I learned it from BRS Physio.
     
  10. goodies

    goodies Member 7+ Year Member

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    the info i got was from BSS (board simulator series)
     
  11. Idiopathic

    Idiopathic Newly Minted Lifetime Donor Classifieds Approved 10+ Year Member

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    AKA: Goljan

    I learned it myself from the man, he has a great diagram.
     
  12. guitarguy09

    guitarguy09 Member 7+ Year Member

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    Apr 23, 2004
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    I just listened to that lecture actually and Goljan clearly states that as well, just as mentioned above. G-dog is the man.
     
  13. winsicle

    winsicle Member 5+ Year Member

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    Dec 15, 2004
    UCLAstudent was talking about the competition b/t H+ and Ca++ for binding sites on Albumin...

    you were talking about the tetany mechanism on neurons:

    which i think just has to do w/ the altered Membrane Potential (due to decreased extracellular/positively-charged 'free' Ca++)
    --> less depolarization is needed to get to the threshold potential and so there is increased firing of AP --> muscle contraction

    (i've never heard of the Na++/Ca++ competition for channels in neurons)
     
  14. SOUNDMAN

    SOUNDMAN Senior Member 10+ Year Member

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    Midwest
    In regards to neurons I believe hypocalcemia leads to tetany by obviously lowering the threshold of the neuron. This occurs d/t Na+ channels becoming more permeable to Na+, and thus more Na+ leaking into the neuron thus lowering the threshold. That's how I've understood it.
     
  15. winsicle

    winsicle Member 5+ Year Member

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    Dec 15, 2004
    yeah the voltage gated Na++ channels become activated b/c of the lowered threshold, but there's no "competition" w/ Ca++
     

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