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30 Cards in this Set

  • Front
  • Back

Cells travel through Hensen's node

Anterior gives rise to

Prechordal, mesoderm notochord and anterior somites

Middle gives rise to

Somites, heart, kidneys

Posterior gives rise to

Lateral plate and extraembryonic mesoderm


Formed by cells deposited by Hensen's node during REGRESSION

Transient mesodermal structure

Important for nervous system


Mesoderm and endoderm move inwards

Ectoderm migrate to surround the yolk

4 days

Cells on the area opaca attatched to vileline envelope

Structures such as filopodia and fibronectin are formed

End of gastrulation

Ectoderm surrounds yolk

Endoderm displaced hypoblast

Mesoderm is between ectoderm and endoderm

Anterior posterior gradient

Anterior posterior axis specification

ovum is rotated as passed through oviduct

blastoderm at the top and yolks lighter contents up

Posterior marginal zone unknown why but equivalent of Nieuwkoops centre

Chicken Bcatenin

stored in blastodisc

vg1 gravitate to posterior Koller sickle

overlap PMZ becomes "Nieuwkoop centre"

Induce nodal


Required for primative streak formation

Cerberus inhibited by secondary hypoblast inhibits primitive streak (wnt)

Hypoblast is replaced by endoblast in PMZ

Streak activates lefty which inhibits additional streaks

Transplant Hensen's node

Induction of a new embryo

Hensons node is like amphibian dorsal blastopore lip

Cells induce a new embryo when transplanted

Induce neural tissue

same genes expressed

cells become prechordal plate/chordamesoderm

Early development in mammals!


Difficult to study human embryos

size of human zygote

Number of eggs produced

Location of development


Cleavage begins 24 hours after fertilization, 1 division per day

Celia push embryo to uterus

Blastocyct sheds zona pellucida and adheres to uterine wall

Mammal Cleavage

Isolecital holoblastic rotational cleavage

1. Slow divisions

2. Rational is different to others

3. Divisions are not symmetrical

4. Genome is activated early - human after 4 divisions


Mouse: loose until 8 cell

Cleavage 3 blastomeres cluster in a ball and accquire polarity with tight and gap junctions

Adhesion molecules - e-cadherin


16 cell

Large group of surface cells and few internal cells

Most external cells form trophoblast- chorion - placenta

Embryo proper- center of morula becomes inner cell mass and develops into embryo, yolk sac and allantois and amnion

ICM 13 cells and trophoblast

ICM pluripotent

Tropho secretes sodium into morula, draws in water, forms cavitation - fluid filled blastocoel

Blastocoel expands, ICM to the side, blastocyst formed

Positional cues and polarity cues

Changes in gene expressions and differentiation

Oustide cells - asymetrical forms trophoectoderm

Inner cells - symetrical forms pluripotent ICM

Hatching and implantation

ZP prevents embryo from implanting in oviduct

Sheds when entering uterus

Blastocyst sheds a hole and squeezes out - trypsin

Binds to uterine epithelium, digest and imbed

Mammal gastrulation

As if large yolk present but uterus and fetal organ chorion are there

Bilaminar germ disk

Epiblast and hypoblast (Made from ICM)

Epiblast closest to uterine wall

Hypoblast cells form

Extraembryonic endoderm

Cells delaminate to line blastocoel

Forms parietal and visceral endoderm

Epiblast cells split into

embryonic epiblast and amnionic ectoderm

Amnionic cavity between

Trophoblast forms

cytrophoblast and syncytiotrophoblast

Further digestion of uterus and formation of placenta

Secrete paracrine factors that attract maternal blood vessels


Trophoblast tissue and blood vessels and extraembryonic mesoderm

Fuses with uterine wall to create placenta

Function of the choiron

1. Provide nutrients and O2 to fetus

2. Secrete hormones into mother to help her retain the fetus

3. Repress mothers immune response to reject fetus

Maternal zygotic twins

Before differentiation of trophoblast

Dichorionic twins - two chorions

Maternal zygotic twins

After one trophoblast has differentiated

monochromatic twins that share choiron

Maternal zygotic twins

after inner cell mass has flattened down to form bilaminar disk stage

Share the same amnion