Placenta - Villi Development

Introduction

This page introduces an overview of aspects of the basic fetal subunit of the placenta, the placental villi development. In early placentation, each villi proceeds through a similar initial program of development. In later placentation, villi morphologically differentiate into a limited range of villi functional changes reflecting their specialization. The major initial contribution is from the trophoblast shell that surrounds the conceptus and later by the development of extraembryonic mesoderm and blood vessel differentiation.

There are three main types of trophoblast cells that differentiate:

1. villous cytotrophoblasts
2. extravillous cytotrophoblasts
3. syncytiotrophoblasts that form by fusion of villous cytotrophoblasts

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.

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Cite this page: Hill, M.A. (2024, May 29) Embryology Placenta - Villi Development. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Placenta_-_Villi_Development

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