Dismiss Notice
SDN members see fewer ads and full resolution images. Join our non-profit community!

Protein-Bound vs. Free (Ionized) Calcium

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

  1. asaha

    Joined:
    Apr 28, 2007
    Messages:
    7
    Likes Received:
    0
    Status:
    Medical Student
    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!
     
  2. Thread continues after this sponsor message. SDN Members do not see this ad.

  3. UCLAstudent

    UCLAstudent I'm a luck dragon!

    Joined:
    Sep 6, 2002
    Messages:
    5,046
    Likes Received:
    7
    Status:
    Resident [Any Field]
    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

    Joined:
    Oct 8, 2005
    Messages:
    334
    Likes Received:
    0
    Status:
    Resident [Any Field]
    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

    Joined:
    Jan 7, 2002
    Messages:
    1,282
    Likes Received:
    3
    Status:
    Resident [Any Field]
    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

    Joined:
    Jul 7, 2005
    Messages:
    229
    Likes Received:
    2
    How many of you learned that from Goljan?
     
  7. doctorp82

    doctorp82 Palpating preschoolers

    Joined:
    Dec 22, 2006
    Messages:
    243
    Likes Received:
    3
    Status:
    Medical Student
    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

    Joined:
    Jan 7, 2002
    Messages:
    1,282
    Likes Received:
    3
    Status:
    Resident [Any Field]
    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!

    Joined:
    Sep 6, 2002
    Messages:
    5,046
    Likes Received:
    7
    Status:
    Resident [Any Field]
    I learned it from BRS Physio.
     
  10. goodies

    goodies Member

    Joined:
    Oct 8, 2005
    Messages:
    334
    Likes Received:
    0
    Status:
    Resident [Any Field]
    the info i got was from BSS (board simulator series)
     
  11. Idiopathic

    Idiopathic Newly Minted
    Lifetime Donor Classifieds Approved

    Joined:
    Apr 21, 2003
    Messages:
    8,363
    Likes Received:
    16
    Status:
    Attending Physician
    AKA: Goljan

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

    guitarguy09 Member

    Joined:
    Apr 23, 2004
    Messages:
    348
    Likes Received:
    0
    Status:
    Resident [Any Field]
    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

    Joined:
    Dec 15, 2004
    Messages:
    190
    Likes Received:
    0
    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

    Joined:
    May 16, 2004
    Messages:
    941
    Likes Received:
    2
    Status:
    Resident [Any Field]
    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

    Joined:
    Dec 15, 2004
    Messages:
    190
    Likes Received:
    0
    yeah the voltage gated Na++ channels become activated b/c of the lowered threshold, but there's no "competition" w/ Ca++
     

Share This Page