Talk:2010 BGD Practical 3 - Gastrulation
|Gastrulation means "gut forming" and converts the inner cell mass which then formed the bilaminar embryo (epiblast, hypoblast) into the trilaminar embryo (ectoderm, mesoderm, endoderm).
The process involves the migration of cells from the epiblast layer through the primitive streak to form first the endoderm layer and then a second intermediate layer the mesoderm layer. Once all cells have left the epiblast layer it now becomes the ectoderm layer.
These three germ cell layers (ectoderm, mesoderm, endoderm) will form in a layer specific manner all the future tissues of the developing embryo.
Carnegie Stage 7 and 8, gastrulation, migration of cells through the primitive streak to form endoderm and mesodermal layers of embryo.
|Trilaminar Embryo Formation
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 Embryo Images).
|File:Stage7n3.jpg||== Carnegie Stages 7 ==
Features: embryonic disc, primitive node, primative streak, primitive groove, yolk sac
Facts: Week 3, 15 - 17 days, 0.4 mm
View 1: embryonic disc, showing the epiblast viewed from the amniotic (dorsal) side.
Events: Gastrulation is continuing as cells migrate from the epiblast, continuing to form mesoderm.
Mesoderm lies between the ectoderm and endoderm as a continuous sheet except at the buccopharyngeal and cloacal membranes. These membranes have ectoderm and endoderm only and will lie at the rostral (head) and caudal (tail) of the gastrointestinal tract.
embryonic disc is shown rostral (head) to top and caudal (tail) to bottom.
Left and right are the lateral margins of the disc as shown.
all edges of the embryonic disc will fold ventrally, forming a rostro-caudal "C" shaped tube.
Through the primitive streak cells migrate continuously through week 3 into week 4. Initial cells replace hypoblast as an epithelial layer the endoderm. Later migrating cells spread between the two epithelial layers to form mesoderm.
- 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.