Normal anatomy

Topic Completed: 1 June 2011

Minor changes: 15 February 2019

Copyright: 2002-2019,, Inc.

PubMed Search: Placenta anatomy [title]

Mandolin S. Ziadie, M.D.
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Page views in 2020 to date: 1,637
Cite this page: Ziadie MS. Normal anatomy. website. Accessed May 30th, 2020.
Definition / general
  • Fetomaternal organ involved in nutrition, waste elimination and gas exchange between the developing fetus and mother
Diagrams / tables

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Gross description
    Parts of placenta
  • Disc: composed of fetal portion (chorionic plate) and maternal portion (basal plate decidua)
  • Divided into cotyledons from primary stem villi and lobules from secondary stem villi
  • Average size at term: 22 cm diameter, 2.0 - 2.5 cm thickness, 470 g

Membranes: composed of amnion, exocoelomic space, chorion and decidual capsularis
  • Usually insert directly onto the placental edge
  • Amnion: innermost covering of amniotic cavity; composed of flat epithelial cells that rest on a thin basement membrane with underlying thin band of loose connective tissue; may show squamous metaplasia, especially near cord or in pregnancies complicated by oligohydramnios
  • Exocoelomic space: potential space between the amnion and chorion which is usually obliterated but allows the membranes to slide against each other
  • Chorion: connective tissue membrane containing fetal vessels, internal to amnion, external to villi
  • Membranous chorion (chorion laeve): formed by collapse of the intervillous space during development; composed of mononuclear, sometimes vacuolated, trophoblasts and scattered atrophic chorionic villi
  • Decidual chorion (chorion frondosum): located in the placenta proper

Umbilical cord:
  • Twisted cable that connects the fetus to the placenta and carries the two umbilical arteries and a single umbilical vein
  • Vessels branch out over the fetal surface to form the villous tree
  • Average size: 55 - 60 cm length and 2.0 - 2.5 cm diameter
Gross images

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Basal plate (maternal surface)

Chorionic plate (fetal surface)

Microscopic (histologic) images

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Basal plate (maternal surface)

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