UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2008)

Acknowledgements

Laboratory 3 - Week 2

Overview of blastocyst implantation in uterine wall during the second week of development. (Image: Moore & Persaud, 1998)

Beginning of Carnegie Stage 6, blastocyst fully implanted in endometrial wall.

Continued expansion of the cavities in the extraembryonic mesoderm, allow the primary yolk sac to collapse. The space formed is lined with extraembryonic mesoderm and forms the third cavity (chorionic). A section of extraembryonic mesoderm adjacent to the bilaminar embryo remains (connecting stalk)

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Glossary

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Terms

• bilaminar- having 2 layers
• blastocyst- the developmental stage following morula, as this stage matures, the zona pellucia is lost allowing the conceptus to adplant and then implant into the uterine wall.
• blastomeres-the cells resulting from the initial rounds of mitotic division of the zygote. These cells become smaller (in cytoplasmic volume) with each division.
• corona radiata- Layer of follicle cells of cumulus oophorus remaining attached to zona pellucida of oocyte after ovulation.
• inner cell mass- the clump of cells found inside the blastocyst. These cells will go in to form the embryo, these are the "stem cells" (we here about in the media) that are totipotential, they can form any tissue in the embryo. Mature oocyte-the female germ cell released at ovulation from the ovary.
• morula &endash;(L. morus = mulberry) early stage of development (12-15 cells) Followed by formation of a cavity in the mass (blastocyst stage). (More? Week 1 Notes)
• parental genomes- the male (sperm) and female (oocyte) DNA which contributes to the embryo's cells.
• polar bodies- 3 exclusion bodies which contain the DNA not used by the embryo. Contributed to initially by the meiotic division of the oocyte.
• pronuclei- the male (sperm) and female (oocyte) nuclei within the fertilized oocyte, prior to their combination to form the new embryo's nuclei.
• trilaminar embryonic disc- the 3 layered embryo stage.
• Trophoblasts- (Gr. trophe = nutrition) outer layer of cells on blastocyst that will generate the embryonic part of the placenta.
• zona pellucida- glycoprotein shell that surrounds the oocyte through to blastula stage of development.
• Zygote- The first cell stage following fertilization of the oocyte by the sperm. This is the first cell of the conceptus which will divide into blastomeres.

Online Resources

UNSW Embryology

Human Menstrual Cycle

Week 1 Development

Week 2 Development

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UNSW Embryology ISBN: 978 0 7334 2609 4

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