RT Book, Section
A1 Neunert, Cindy E.
A1 Yee, Donald L.
A2 Rudolph, Colin D.
A2 Rudolph, Abraham M.
A2 Lister, George E.
A2 First, Lewis R.
A2 Gershon, Anne A.
SR Print(0)
ID 7040718
T1 Chapter 439. Disorders of Platelets
T2 Rudolph's Pediatrics, 22e
YR 2011
FD 2011
PB The McGraw-Hill Companies
PP New York, NY
SN 978-0-07-149723-7
LK accesspediatrics.mhmedical.com/content.aspx?aid=7040718
RD 2024/04/25
AB Platelets  arise  from  megakaryocytic  precursors  in  the  bone  marrow.  Maturation  and  production  is  regulated  by  several  general  cytokines  and  the  more  specific  platelet  growth  factor,  thrombopoietin.  Platelet  production  occurs  through  the  specialized  process  of  endomitosis,  by  which  DNA  replicates  without  cell  division,  resulting  in  the  polyploid  nuclei  characteristic  of  megakaryocytes.1  Proplatelet  extensions  form  from  megakaryocytic  cytoplasm;  once  granule  and  cytoplasmic  organization  is  complete,  platelets  are  released  from  the  ends  of  the  proplatelet  structures.  After  leaving  the  marrow,  approximately  one  third  of  the  platelet  mass  is  sequestered  in  the  spleen,  while  the  other  two  thirds  circulate  with  a  life  span  of  7  to  10  days.  Thrombopoiesis  is  balanced  by  platelet  senescence  and  consumption  to  maintain  a  normal  blood  platelet  count  (150,000–400,000/mm3)  via  the  plasma  thrombopoietin  level.  Platelets  have  an  average  diameter  of  2.0  to  5.0  mm  and  typical  mean  platelet  volumes  of  6  to  10  femtoliters.1  Their  external  surface  consists  of  a  lipid  bilayer  containing  a  variety  of  structural  glycoproteins.  The  anuclear  cytoplasm  contains  dense  granules,  which  store  calcium,  serotonin,  adenosine  diphosphate  (ADP),  and  adenosine  triphosphate  (ATP),  and  the  more  numerous  alpha  granules,  which  contain  other  biologically  active  proteins  including  fibrinogen,  von  Willebrand  factor,  factor  V,  and  other  adhesive  molecules.