Embryonic period
Development 149
Organogenesis: 3.-8. week
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Formation of all organ systems:
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Cardiovascular and nervous - 3.week
External genitalia – later than 8.week
Changes in outer shape
Most critical period
Growth
Beginning of embryonic period
embryo, stage 10, 23ED
according Carnegie classification
3,0mm
The end of embryonic period
Embryo, stage 23 , 56ED
according Carnegie classification
30,0 mm
Formation of 3D shape
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Head fold
Tail fold
Lateral folds
Head fold - growth of brain and spinal cord – folding
(septum transversum and heart are pushed ventrally)
Changes in shape of intraembryonic coelomic cavity
Tail fold – cloacal membrane is also pushed ventrally
Lateral folds – gut closure, formation of umbilical cord
Differentiation of intraembryonic mesoderm
transversal
section
Differentiation of intraembryonic mesoderm
transversal
section
Longitudinal and lateral folding
cervical and caudal
folds – 2 tranversal
folds
lateral foldings
contribute to
yolk/umbilical sac
invagination to the
body of the embryo
Growth
•
proliferation + extracellular matrix synthesis + cavities
formation
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caudal morphogenetic system (cms) – principal growth
centre, embryo extension
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head region – early growth - expansion, later growth during
fetal period
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differentiation in head is an advance in early embryo
Segmentation
neuroectoderm a mesoderm
neuromeres - neuroectoderm, CNS – brain vesicles
somitomeres - somites - paraxial mesoderm
homeotic genes, HOX – rhombencefalon,
rhombomeres
OTX1, OTX2, EMX1, EMX2 – mesencephalon,
prosencephalon
Neural tube development in brain region
(segmentation in neuroectoderm - neuromeresbrain vesicles)
3 primary brain vesicles
wall
5 secondary brain vesicles
adult derivates
wall
cavity
forebrain
midbrain
hindbrain
cavities
Organogenesis
Derivatives of the three germ
layers
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Ectoderm – CNS, PNS, retina, epidermis, mammary gland,
enamel
Cells of neural crest -– ganglia, Schwann´s cells,
melanocytes, medulla of suprarenal gland, meninx,
muscle, connective tissue and cartilages/ bones of
pharyngeal arches
Mesoderm – connective tissue, cartilage, bone, muscle,
vessels, kidney, ovary, testes, spleen, cortex of suprarenal
gland, mesothelium
Endoderm – digestive and respiratory system (epithelium
and glands), thyroid gland, parathyroid glands, thymus,
pancreas, liver, urinary bladder
CS9 (ED19-21)
Segmentation in paraxial mesoderm
4th week
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Closureof rostral and caudal neuroporus (24th and
26th day)
Somites (4.-12.)
Pharyngeal arches are visible by 26th day
Heart prominence
Upper limb buds 26th- 27th day
Otic pits and lens placodes
Lower limb buds – by the end of week
Tubular embryo SC11 (ED23-26)
5th week
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Head growth – brain and pharyngeal arches
Pharyngeal arches – development of face
and neck
Ectodermal grooves and endodermal
pouches, pharyngeal membranes
Aortic arches – vessels in pharyngeal arches
SC13 (ED23-32)
6th week
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Development of limbs – future fingers –
digital rays are visible
Development of ear: external acustic
meatus(first pharyngeal groove), swelling
around it fuse to form auricle
Head is larger than body
C-shaped embryo (CS14 – ED31-35)
7th week
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Development of limbs – digits of upper
limbs
Umbilical herniation– intestine enters the
extraembryonic coelom in the proximal
region of umbilical cord.
8the week
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Digits also in lower limbs
Tail disappears at the end of 8th week
Embryo has distinct human characteristics
– head constitutes almost ½ of embryo
Eyes – eye lids fuse by end of 8th week
External genitalia - indifferent
Fetal period
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By 9th week till birth
Biparietal distance, head
circumference,body circumference, femur
length,
Disorder – IUGR – intrauterinne growth
retardation – reduction of vascular supply,
placental insufficiency
Estimation of age
From last menstrual bleeding
From fertilization
According to sonography
According to morphologic features
Length (in 3+4 week) whole embryo including
chorion
Stages according to Carnegie
Length from top of the head to the coccyx