Talk:2010 BGD Practical 3 - Week 2 Summary
Implantation Sites - Normal and Abnormal
File:Implant.jpgSites of normal and abnormal blastocyst implantation.
Site of most common (normal) implantation is the posterior wall of uterus (shown by X). Abnormal implantation: tubal pregnancies (shown by A-F), ovarian (H), and abdominal (G). Implantation at the internal os generates the clinical condition placenta previa, (resulting in bleeding or placental separation during pregnancy). Note that spontaneous abortion of blastocysts is quite common and studies of blastocysts that do not implant indicate chromosomal abnormalities in many of these embryos.
Implantation Images Day 8 and 9
File:Day8and9.jpgOverview of blastocyst implantation in uterine wall during the second week of development. (Image: Moore & Persaud, 1998)
Identify the embryoblast and trophoblast layers of the conceptus.
Carnegie Stage 4 (stages 1-23 describing key steps in embryonic development) represents the beginning of implantation.
The blastocyst initially attached to the uterine endometrium (adplantation), syncitiotrophoblasts then secrete enzymes that digest extracellular matrix, allowing the blastocyst to sink into the uterine wall, eventually being completely enclosed within the uterine wall. Note the majority of growth occurs in the trophoblastic shell. The inner cell mass divides initially into 2 layers; epiblast and hypoblast (bilaminar embryo). Hypoblast cells migrate around the original blastoceol cavity forming the primary yolk sac. A second cavity (amniotic) forms between the inner cell mass and the cytotrophoblast shell; this cavity is lined by epiblast cells.
Now consider abnormal events taht may occur in development during the second week. This involves abnormalities of implantation and conceptus development. [../Notes/week2_2.htm Week 2 Abnormalities]
- 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.