UNSW Embryology

Beginnings, Growth and Development

© Dr Mark Hill (2006)

Acknowledgements

Laboratory 3 - Week 3

Carnegie Stage 7 and 8, gastrulation, migration of cells through the primitive streak to form endoderm and mesodermal layers of embryo.

Carnegie stage 7 embryonic disc viewed from ectodermal (amniotic) surface.

Identify primitive streak, primitive pit and primitive node (of Hensen). Connecting stalk to left.

Carnegie Stage 8 embryonic disc (similar view above).

From the primitive pit (in opposite direction to streak) will extend a fold of ectoderm, the beginning of notochordal process.

Scanning electron micrograph through the streak region showing the early forming 3 layers: ectoderm, mesoderm and endoderm. (from Embryo Images by Dr K.K. Sulik & P. Bream, diagram from Langman's Medical Embryology by T.W. Sadler) (http://www.med.unc.edu/embryo_images/unit-bdyfm/bdyfm_htms/bdyfm003.htm).

Stage 7

Next

Link to next page in this Practical 3 - Notochord

Glossary

• 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 (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

Quick Links

UNSW Embryology ISBN: 0 7334 2321 3

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