File:Placenta anchoring villi.jpg
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Placenta Anchoring Villi
Histological image showing the junctional region between the maternal decidua (left) and the embryonic placental villi (right).
- In week 2, the trophoblast shell cells proliferate and form a syncitiotrophoblast and cytotrophoblast layer around he conceptus.
- Syncitiotrophoblast cells migrate into the uterine wall, forming maternal blood-filled spaces (lacunae).
Placentation begins once the conceptus begins to implant in the uterine wall and the placenta will have both a fetal and a maternal component. The fetal component begins as villi form. The fetal chorion will form two regions: smooth chorion (chorion laeve) and villous chorion (chorion frondosum).
The maternal component is formed by the decidualization of the endometrium.
- Decidualization - (decidualisation) is the process by which uterine stromal cells differentiate in response to both steroid hormones (progesterone) and embryonic signals into large epitheliod decidual cells. This process is essential for the progress of implantation and establishing fetal-maternal communication.
- Decidual cells form from the uterine stromal cells (fibroblast-like) that differentiate in response to hormonal and embryonic signals and then alter uterine environment to support further embryonic development as well as producing cytokines related to prolactin (PRL) and have an innate immune function.
- Fibrinoid layer (Nitabuch's layer) is formed at maternal/fetal interface during placentation and is thought to act to prevent excessively deep conceptus implantation.
- Fibrin-type fibrinoid - maternal blood-clot product)
- Matrix-type fibrinoid - secreted by invasive extravillous trophoblast cells
Image Source: UNSW Embryology, no reproduction without permission.
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|current||14:37, 3 August 2009||600 × 450 (167 KB)||MarkHill||Placenta anchoring villi Histological image showing the junctional region between the trophoblast shell of the conceptus and the maternal decidua. In week 2, the trophoblast shell cells proliferate and form a syncitiotrophoblast and cytotrophoblast lay|