Talk:ANAT2341 Lab 4 - Implantation and Villi Development
Old Virtual slide link (replaced by BEST link)
|Implantation||Chorionic Cavity||Week 3||Amniotic Cavity|
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Mesenchymal villi continuously form out of the trophoblastic sprouts throughout pregnancy and have been considered the basis for growth and differentiation of the villous trees.
Mesenchymal villi generate all other villous types:
- immature and mature intermediate villi
- stem villi - or anchoring villi, cytotrophoblast cells attached to maternal tissue.
- terminal villi - not active outgrowths caused by proliferation of the trophoblast. Passive protrusions induced by capillary coiling due to growth of the fetal capillaries within the mature intermediate villi (third trimester).
- branched villi - grow from sides of stem villi, region of main exchange, surrounded by maternal blood in intervillous spaces.
Originally villi cover entire chorionic surface and then become restricted to decidua basalis region forming 2 regions:
- Frondosum - "leafy" where villi are mainly located.
- Capsularis - smooth chorion, where villi are absent or not abundant.
|ANAT2341 Lab 4: Introduction | Implantation and Villi | Decidua and Cord | Abnormal Placenta | Cardiovascular | Online Assessment | Group Project|
Human Villi Timeline
The placental vill development data below is based upon a recent immunochemistry confocal laser scanning microscope (CLSM) study.
Note that the paper uses clinical gestational age (GA) from last menstrual period (LMP) and has been corrected for post-conception (fertilization) age, approximately 14 days later.
|Vessel Lumen Diameter
(range in microns, µm)
|3 to 4||5 and 6||10 - 15||
|5 to 6||7 and 8||10 - 26||
|7 to 8||9 and 10||60 - 75 two central vessels
26 - 34 capillary network
|9 to 10||11 and 12||70 - 90 two central vessels
26 - 34 capillary network
There is a new interpretation of the changes that are occuring in the cytotrophoblast (CTB) layer during early to full-term human placenta development. Traditionally the interpretation was that the cytotrophoblast layer thinned and became discontinuous towards term. The thinning is thought due to the epithelium surface expanding at a faster rate than its volume. Two recent studies suggest that while the cytotrophoblast layer does indeed thin, it does not become discontinuous.
The syncytiotrophoblast (STB) layer forms the epithelial covering of the entire villous tree. These cells are multinucleated, terminally-differentiated syncytium formed by the fusion of the underlying progenitor cytotrophoblast (CTB) cells. The process is described as "syncytialization" and is mediated by syncytin-1, an envelope protein of a human endogenous retrovirus W (HERV-W). The differentiation is regulated by chorionic gonadotropin (hCG) and the fusion of cytotrophoblast cells is ongoing during placental development.
Cellular parts derived from the syncytiotrophoblasts (apoptotic nuclei and microparticulate debris) can be shed into the maternal blood in which they are bathed. The apototic process appears to be part of the fusion mechanism between cytotrophoblast and the overlying multinucleate syncytiotrophoblast layer.
Studies have suggested that these cells are transcriptionally inactive. A recent study using a number of different detection techniques now suggests that at least some of the cells nuclei may still be transcriptionally inactive.