1

Fertilization & Implantation

Topics for today:

• Blastula and implantation• Formation of chorion• Gastrula & Tissue differentiation• Neurula and organogenesis• Limb bud stage

Implantation

day 7endometriumovulation

morula

blastula

fertilization

mitosis

Chorion formation & releaseof chorionic gonadotropin

2

Early Embryo Stages

Zygote morula blastula ovum

spermatozoan

cleavagefertilization0 d 3 d

stage atimplantation

5 dblastulation

Undifferentiated embryo stem cells

Mid to Late Embryo Stages

blastula gastrula neurula18 d 8 d

gastrulation

Undifferentiated inner cell mass

neurulation

blastula gastrula

Inner cell mass splits to 2 layers(differentiation begins)

gastrocoele

day 7 day 8-9

Chorion formation &release of HCG

releases HCG

day 7

Beginning formation of chorion,first layer of developing placenta

Chorion releases chorionicgonadotropin (HCG), a hormonewhich tells corpus luteum tocontinue release of progesterone

Progesterone is essential formaintenance of placenta

3

Extra embryonic membranesMembranes that support development

of embryo proper

• Chorion - outermost; 1st to appear

• Amnion - contains amnionic fluid; 2nd

• Yolk Sac - gives rise to gut; 3rd

• Amnion - bladder precursor; last

Gastrulation...beginning of tissue development

day 10

amnion

early ectoderm

early endoderm

chorion

Late gastrula stageMesoderm

forming

day 12

4

Neurula stage of developmentNeurula Neurula stage of developmentstage of development

Brainregion

Spinal cordregion

About 2 weeks old

Dorsal view showingdeveloping nerve cord

Developing somites(body segments) visible

Period of extensive organ development

SEM view of neurula stage(transverse view of neural tube)

neural tube

notochord

dorsal aortae

gut

About 3 wks

Formation of yolk sac

Week 3-4

5

Brainregion

Limbbuds

Jaws

Late embryo with limb buds

Eye

Heart

About 4 wks

Late embryo & the placenta

Topic for Wednesday:

Fetus and Parturition