Prenatal Periods

Prenatal Periods

1. Germinal period- period of the Zygote

   • period of rapid cell replication
   • conception till implantation (end of second week)
   • formation of the blastocyst with two layers
     • outer cell mass: trophoblast layer
     • inner cell mass: embryonic disk

2. Embryonic period

   • implantation till the end of the eight week of gestation
     • eight week- movement begins and bones begin to harder
   • basic organs are formed (organogenesis) and embryo responds to direct stimulation
   • embryonic disk is differentiated into three cell layers
     • ectoderm- nervous system, skin and hair
     • mesoderm- muscles, bones, circulatory system and internal organs
     • endoderm- digestive system, lungs, urinary tract and glands

3. Foetal period- period of the foetus

   • organs take their final forms and begin to function (histogenesis)
   • divided into trimesters (3 periods of 3 months)
   • begins two thirds of the way through the first trimester and ends at birth (8th week - birth)