RT Book, Section
A1 Rabaglia, Jennifer L.
A1 Moore, Francis D.
A2 Morita, Shane Y.
A2 Dackiw, Alan P. B.
A2 Zeiger, Martha A.
SR Print(0)
ID 6162914
T1 Chapter 10. Secondary and Tertiary Hyperparathyroidism
T2 McGraw-Hill Manual: Endocrine Surgery
YR 2010
FD 2010
PB The McGraw-Hill Companies
PP New York, NY
SN 978-0-07-160645-5
LK accesssurgery.mhmedical.com/content.aspx?aid=6162914
RD 2023/03/29
AB The  precise  regulation  of  the  serum  ionized  calcium  concentration  is  necessary  to  sustain  human  life.  The  calcium  cation  is  central  to  a  myriad  of  reactions,  from  enzymatic  function  to  the  coagulation  cascade  to  muscle  fiber  contraction  and  neurotransmission  to  the  dynamic  buildup  and  breakdown  of  the  scaffolding  that  houses  it  all.  The  majority  of  calcium  in  the  human  body  is  found  in  the  skeleton  and  comprises  approximately  2%  of  the  average  individual's  body  weight.  Serum  calcium  levels  are  precisely  maintained  through  an  intricate  interplay  of  checks  and  balances  that  begin  and  end  with  the  parathyroid  glands.  The  regulatory  axis  of  calcium  consists  of  the  parathyroid  glands,  parathyroid  hormone  (PTH),  membrane  calcium  receptors,  the  kidneys,  the  gut,  and  bone.  Membrane  calcium  receptors  on  the  cells  of  the  parathyroid  glands  sense  minute  decreases  in  serum  ionized  calcium  levels,  triggering  a  cascade  beginning  with  the  secretion  of  PTH.  This  stimulates  mobilization  of  calcium  from  bone,  a  reduction  in  renal  calcium  excretion,  and  an  increase  in  renal  hydroxylation  of  vitamin  D,  indirectly  affecting  calcium  absorption  in  the  duodenum  and  proximal  jejunum.  When  calcium  increases  to  within  an  acceptable  range,  calcium  receptor-based  stimulation  of  the  parathyroids  ceases,  and  secretion  of  PTH  is  inhibited.  Thus,  under  normal  conditions,  the  defining  relationship  between  serum  calcium  and  serum  PTH  is  inverse:  that  is,  high  serum  calcium  begets  low  serum  PTH  and  vice  versa.