The temporary anatomical structures prominent in the first trimester may be fulfilling exchange functions assigned to the placenta in the second and third trimester.
The extra-embryonic coelom (EEC) and secondary yolk sac are prominent structures in the gestational sac during the first trimester of human pregnancy, at a time before the definitive placental circulation becomes established. We propose that the EEC and yolk sac play a critical role in the nutrition of early pregnancy, fulfilling exchange functions which are assumed by the placenta at a later stage.
Docherty
S M
SM
Department of Obstetrics, St. Bartholomew's Hospital Medical College, West Smithfield, London EC1A 7BE, UK.
Iles
R K
RK
Wathen
N
N
Chard
T
T
D000653:Amniotic Fluid / Q000737:chemistry; D005260:Female; D006801:Humans; D018970:Insulin-Like Growth Factor Binding Protein 1 / Q000032:analysis; D008648:Mesoderm / Q000502:physiology; D010920:Placenta / Q000502:physiology*; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000502:physiology*; D011388:Prolactin / Q000032:analysis; D015017:Yolk Sac / Q000502:physiology*
D018970:Insulin-Like Growth Factor Binding Protein 1; D011388:Prolactin