TY  - CHAP
M1  - Book, Section
TI  - Hematology of the Fetus and Newborn
A1  - Palis, James
A1  - Segel, George B.
A2  - Kaushansky, Kenneth
A2  - Prchal, Josef T.
A2  - Burns, Linda J.
A2  - Lichtman, Marshall A.
A2  - Levi, Marcel
A2  - Linch, David C.
PY  - 2021
T2  - Williams Hematology, 10e
AB  - SUMMARYDuring  embryogenesis,  hematopoiesis  occurs  in  spatially  and  temporally  distinct  sites,  including  the  extraembryonic  yolk  sac,  the  fetal  liver,  and  the  preterm  marrow.  The  development  of  primitive  erythroblasts  in  the  yolk  sac  is  critical  for  embryonic  survival.  Nucleated  primitive  erythroblasts  differentiate  within  the  vascular  network  rather  than  in  the  extravascular  space  and  ultimately  enucleate  upon  terminal  differentiation.  Macrophage  and  multipotential  myeloid  progenitors  initially  arise  in  the  early  yolk  sac  and  provide  specialized  tissue-resident  macrophage  populations  that  persist  into  adulthood  in  multiple  organs,  including  the  brain,  liver,  and  lungs.  Definitive  erythroid  progenitors  also  arise  in  the  yolk  sac  and  seed  the  early  fetal  liver  to  generate  red  cells  until  the  establishment  of  blood  cell  production  from  hematopoietic  stem  cells.  Hematopoietic  stem  cells  emerge  from  major  arterial  vessels  at  5  weeks  of  gestation  and  seed  the  liver  and  ultimately  the  marrow  to  provide  lifelong  hematopoiesis.  The  liver  serves  as  the  primary  source  of  red  cells  from  the  9th  to  the  24th  week  of  gestation.  Hematopoiesis  in  the  fetal  liver  consists  not  only  of  definitive  erythroid,  megakaryocyte,  and  multiple  myeloid  lineages  but  also  lymphoid  lineages.  B-cell  progenitors  are  present  in  the  fetal  liver  beginning  at  7  weeks  of  gestation  and  expand  rapidly  in  the  bone  marrow  from  11–20  weeks  of  gestation.  Lymphopoiesis  is  also  present  in  the  lymph  plexuses  and  the  thymus  beginning  at  9  weeks  of  gestation.  Hemoglobin  (Hgb)  Gower-1  (ζ2ε2)  is  the  major  hemoglobin  in  embryos  younger  than  5  weeks.  Hgb  F  (α2γ2)  is  the  major  hemoglobin  of  fetal  life.  The  fetal  hemoglobin  concentration  in  blood  decreases  after  birth  by  approximately  3%  per  week  and  is  generally  less  than  2%  to  3%  of  the  total  hemoglobin  by  6  months  of  age.  The  mean  hemoglobin  level  in  cord  blood  at  term  is  16.8  g/dL,  with  95%  of  the  values  falling  between  13.7  and  20.1  g/dL.  The  red  cells  of  a  newborn  are  macrocytic,  with  a  mean  cell  volume  in  excess  of  110  fL.  The  red  cell,  hemoglobin,  and  hematocrit  values  decrease  only  slightly  during  the  first  week  after  birth  but  decline  more  rapidly  in  the  following  5–8  weeks,  producing  the  physiologic  anemia  of  the  newborn.  The  absolute  number  of  neutrophils  in  the  blood  of  term  and  premature  infants  is  usually  greater  than  that  found  in  older  children.  Segmented  neutrophils  are  the  predominant  leukocytes  in  the  first  few  days  after  birth.  As  their  number  decreases,  the  lymphocyte  becomes  the  most  numerous  cell  type  and  remains  so  during  the  first  4  years  of  postnatal  life.  Phagocytosis  of  bacteria  by  neutrophils  from  premature  and  term  infants  is  normal.  Bactericidal  activity  varies  according  to  the  conditions  of  testing  and  the  clinical  status  of  the  neonate.  The  platelet  counts  in  term  and  preterm  infants  are  between  150  and  400  ×  109/L,  comparable  to  adult  values.  The  absolute  number  of  lymphocytes  in  newborns  is  equivalent  to  that  in  older  children,  with  lower  values  in  premature  infants  at  birth.  The  absolute  number  of  CD3+  and  CD4+  (helper/inducer  phenotype)  T-cell  subsets  in  blood  of  newborns  is  significantly  higher  than  in  adults.  Humoral  (B-cell)  ...
SN  - 
PB  - McGraw-Hill Education
CY  - New York, NY
Y2  - 2024/04/19
UR  - hemonc.mhmedical.com/content.aspx?aid=1180476372
ER  -