File:Placenta anchoring villi.jpg

From Embryology

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Placenta Anchoring Villi

Histological image showing the junctional region between the maternal decidua (left) and the embryonic placental villi (right). (Stain - Haematoxylin Eosin)

  • 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).

Maternal Decidua

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

Placenta Links: placenta | Lecture - Placenta | Lecture Movie | Practical - Placenta | implantation | placental villi | trophoblast | maternal decidua | uterus | endocrine placenta | placental cord | placental membranes | placenta abnormalities | ectopic pregnancy | Stage 13 | Stage 22 | placenta histology | placenta vascular | blood vessel | cord stem cells | 2013 Meeting Presentation | Placenta Terms | Category:Placenta
Historic Embryology - Placenta 
1883 Embryonic Membranes | 1907 Development Atlas | 1909 | 1910 Textbook | 1917 Textbook | 1921 Textbook | 1921 Foetal Membranes |1921 human | 1921 Pig implantation | 1922 Single placental artery | 1923 Placenta Review | 1939 umbilical cord | 1943 human and monkey | 1944 chorionic villus and decidua parietalis | 1946 placenta ageing | 1960 first trimester placenta | 1960 monkey | 1972 Placental circulation | Historic Disclaimer

| Implantation


Image Source: UNSW Embryology, no reproduction without permission.

Cite this page: Hill, M.A. (2024, April 24) Embryology Placenta anchoring villi.jpg. Retrieved from

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G

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current14:37, 3 August 2009Thumbnail for version as of 14:37, 3 August 2009600 × 450 (167 KB)MarkHill (talk | contribs)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