ANAT2341 Lab 4 - Implantation and Villi Development

From Embryology
ANAT2341 Lab 4: Introduction | Implantation and Villi | Decidua and Cord | Abnormal Placenta | Cardiovascular | Online Assessment | Group Project

Implantation

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Human Embryo Day 8 to 9

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 Implantation  Chorionic Cavity  Week 3  Amniotic Cavity
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Villi Development

Chorionic Villi

Primary villi

Week 2 - first stage of chorionic villi development, trophoblastic shell cells (syncitiotrophoblasts and cytotrophoblasts) form finger-like extensions into maternal decidua.

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Secondary villi

Week 3 - second stage of chorionic villi development, extraembryonic mesoderm grows into villi, covers entire surface of chorionic sac.

Basal region will form chorionic plate.

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Tertiary villi

Week 4 - third stage of chorionic villi development, mesenchyme differentiates into blood vessels and cells, forms arteriocapillary network, fuse with placental vessels, developing in connecting stalk.

  • stem villi - or anchoring villi, cytotrophoblast cells attached to maternal tissue.
  • branched villi - grow from sides of stem villi, region of main exchange, surrounded by maternal blood in intervillous spaces.
  • 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).
  • chorionic plate - region of membrane at the base of the villi through which placental arteries and vein passes.
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Anchoring Villi

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Floating Villi

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Chorionoic Villi Location

Originally villi cover entire chorionic surface and then become restricted to decidua basalis region forming 2 regions:

  1. Frondosum - "leafy" where villi are mainly located.
  2. Capsularis - smooth chorion, where villi are absent or not abundant.
Embryo-membranes stage 11.jpg Stage18 bf10.jpg
Week 4 (Stage 11)
Week 7 (Stage 18)

Additional Information

Placental villi cartoon

Cytotrophoblast Layer

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.

Syncytiotrophoblast Layer

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.

Mesenchymal Villi

Mesenchymal villi generate all other villous types:

  • immature intermediate villi
  • stem villi
  • mature intermediate villi
  • terminal villi

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.

ANAT2341 Lab 4: Introduction | Implantation and Villi | Decidua and Cord | Abnormal Placenta | Cardiovascular | Online Assessment | Group Project

Additional Information

Human Villi Timeline

The placental vill development data below is based upon a recent immunochemistry confocal laser scanning microscope (CLSM) study.[1]

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.

Fertilization Age

(weeks)

Gestational Age

(weeks)

Vessel Lumen Diameter

(range in microns, µm)

Features
3 to 4 5 and 6 10 - 15
  • a complex network of cords and vessels with redundant connections
  • network comprises mainly cords, already connected together
  • vessels and cords are connected to each other without any interruptions
  • chorionic villus dominated by this network of vascular elements
  • vessels and cords are located centrally as well as peripherally and as a consequence contact the overlying trophoblastic layer
5 to 6 7 and 8 10 - 26
  • villi dominated by capillary network of vessels and cords
  • capillary network contains more vessels than cords
7 to 8 9 and 10 60 - 75 two central vessels

26 - 34 capillary network

  • villi have two large centrally located vessels
  • surrounded by and connected to a peripheral capillary network
  • capillary network contains vessels with a lumen in tight contact with overlying trophoblastic layer
  • villous projections also contain blind ending capillary sprouts
9 to 10 11 and 12 70 - 90 two central vessels

26 - 34 capillary network

  • immature intermediate villi characterized by two large vessels surrounded by a capillary network
  • capillary network has few cords
  • blind ending capillary sprouts off the capillary network

Reference

  1. <pubmed>17545656</pubmed>



ANAT2341 Lab 4: Introduction | Implantation and Villi | Decidua and Cord | Abnormal Placenta | Cardiovascular | Online Assessment | Group Project
2012 Course: Week 1 Lecture 1 Lecture 2 Lab 1 | Week 2 Lecture 3 Lecture 4 Lab 2 | Week 3 Lecture 5 Lecture 6 Lab 3 | Week 4 Lecture 7 Lecture 8 Lab 4 | Week 5 Lecture 9 Lecture 10 Lab 5 | Week 6 Lecture 11 Lecture 12 Lab 6 | Week 7 Lecture 13 Lecture 14 | Lab 7 | Week 8 Lecture 15 Lecture 16 Lab 8 | Week 9 Lecture 17 Lecture 18 Lab 9 | Week 10 Lecture 19 Lecture 20 Lab 10 | Week 11 Lecture 21 Lecture 22 Lab 11 | Week 12 Lecture 23 Lecture 24 Lab 12


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Cite this page: Hill, M.A. (2021, September 17) Embryology ANAT2341 Lab 4 - Implantation and Villi Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/ANAT2341_Lab_4_-_Implantation_and_Villi_Development

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© Dr Mark Hill 2021, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G