Placenta - Normal anatomy

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Placenta

Normal anatomy

Reviewers: Mandolin Ziadie, M.D., (see Reviewers page)
Revised: 13 November 2011, last major update June 2011
Copyright: (c) 2003-2011, PathologyOutlines.com, Inc.

Definition
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● Fetomaternal organ involved in nutrition, waste elimination and gas exchange between the developing fetus and mother

Gross description (Macroscopy)
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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:
● A twisted “cable” that connects the fetus to the placenta and carries the two umbilical arteries and a single umbilical vein
● The 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

Drawings
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Placenta

Gross images
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Basal plate (maternal surface)

Chorionic plate (fetal surface)

Micro images
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Basal plate (maternal surface)

Chorionic plate (fetal surface)

End of Placenta > Normal anatomy

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