EMBRYOLOGY III – handouts
1. Important events in the first week of embryonic development
 fertilization
 cleavage, blastomers
 blastogenesis
 implantation and changes in trophoblast
 embryogenesis
2. Important events in the second week of embryonic development
 differentiation of embryoblast
 bilaminar germ disc, epiblast and hypoblast
 development of amniotic cavity
 primary yolk sac
 extraembryonic coelom
 extraembryonic mesoderm
3. Important events in the third week of embryonic development
 trilaminar germ disc
 differentiation of epiblast
 primitive streak and primitive (Hensen’s) node
 development of intraembryonic mesoderm
 differentiation of ectoderm and neuroectoderm
 differentiation of intraembryonic mesoderm and somitogenesis
4. Principles of embryonic induction and determination
 intraembryonic mesoderm
 notochord and induction of neurulation
 neural tube and neural crest (crista neuralis)
5. Gastrulation and embryonic flexion, derivatives of intraembryonic mesoderm
6. Overview of embryogenesis, from week 4 to week 8
 Mesoderm segmentation
 Primitive gut
 Esophagotracheal diverticulum
 Heart (starts beating day 22-23)
 Limb buds
 Primary brain vesicles, closing of neuropores
 Differentiation of neural crest
 Origin of thyroid and anterior pituitary
 Ectodermal placodes, optic vesicle
 Liver diverticulum
 Septum transversum
 Mesoderm segmentation
 Primitive gut
 Esophagotracheal diverticulum
 Heart (starts beating day 22-23)
 Limb buds
 Primary brain vesicles, closing of neuropores
 Differentiation of neural crest
 Origin of thyroid and anterior pituitary
 Ectodermal placodes, optic vesicle
 Liver diverticulum
 Septum transversum
 Mesoderm segmentation
 Primitive gut
 Esophagotracheal diverticulum
 Heart (starts beating day 22-23)
 Limb buds
 Primary brain vesicles, closing of neuropores
 Differentiation of neural crest
 Origin of thyroid and anterior pituitary
 Ectodermal placodes, optic vesicle
 Liver diverticulum
 Septum transversum
 Secretion from endocrine pancreas
 Growth of liver, growth and luminization of bile ducts
 Ossification of limbs begin
 Development of brain nuclei
 Joints of upper and later lower limbs allow rotation
 Fingers grow
 Stratification of cerebellar cortex
 Perforation of anal membrane
 Herniation of intestinal loops
 Testes produce testosterone
 Nose, meatus, eyelids, developer, external ears start to grow
 Backbone - 33-34 cartilaginous vertebrae
 Embryonic tail diminished
6. Length of pregnancy
 Calculation, rule of Hasse
7. Overview of fetal development from week 8 to birth
8. Hallmarks of fetal maturity
 major and minor
 Rule of Hasse
9. Head size
 diameter bitemporalis
 diameter biparietalis
 diameter frontooccipitalis
 circumferentia frontooccipitalis
 diameter suboccipitobregmatica
 circumferentia suboccipitobregmatica
 diameter mentooccipitalis
 circumferentia mentoocipitalis
 diameter biacromialis
 circumferentia biacromialis
• Fetus swallows amniotic fluid – necessary for GIT development
• Rapid growth of head (non-proportional to rest of body)
• Eyelids fuse
• Ossification centers visible by ultrasound examination
• Development of external genitalia
• Kidneys produce urine, other organs start to work
• Skeletal muscles innervated
• Physiological umbilical hernia, in 12th weeks reposition of intestinal loops
• Rapid growth of fetus
• Ossification of skeleton
• Face growths, mandible visible
• Apparent external genitalia
• Grey zone of viability (22-24 week)
• Limbs growth
• Mother feels fetal movements
• Vernix caseosa, lanugo
• Short hairs and eyelashes
• Fetus reacts to sound and later to light
• Lungs start to produce surfactant
• Limit of viability (full care provided)
• Eyelids open
• Wrinkled skin with visible capillaries
• Subcutaneous fat
• Hairs grow
• Maturing of organ systems
• Subcutaneous fat accumulates in limbs
• Smooth, red skin
• Hallmarks of full term fetus
10. Fetus in uterus
 Situs
 Positio
 Habitus
 Praesentation
11. Introduction to teratology and prenatal diagnostics
 Teratogens
 Critical periods during development