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Fetus in Utero between Fifth and Sixth Months

Fetal Portion

The fetal portion of the placenta consists of the villi of the chorion frondosum; these branch repeatedly, and increase enormously in size. These greatly ramified villi are suspended in the intervillous space, and are bathed in maternal blood, which is conveyed to the space by the uterine arteries and carried away by the uterine veins. A branch of an umbilical artery enters each villus and ends in a capillary plexus from which the blood is drained by a tributary of the umbilical vein. The vessels of the villus are surrounded by a thin layer of mesoderm consisting of gelatinous connective tissue, which is covered by two strata of ectodermal cells derived from the trophoblast: the deeper stratum, next the mesodermic tissue, represents the cytotrophoblast or layer of Langhans; the superficial, in contact with the maternal blood, the syncytiotrophoblast. After the fifth month the two strata of cells are replaced by a single layer of somewhat flattened cells.

Maternal Portion

The maternal portion of the placenta is formed by the decidua placentalis containing the intervillous space. As already explained, this space is produced by the enlargement and intercommunication of the spaces in the trophoblastic network. The changes involve the disappearance of the greater portion of the stratum compactum, but the deeper part of this layer persists and is condensed to form what is known as the basal plate. Between this plate and the uterine muscular fibres are the stratum spongiosum and the boundary layer; through these and the basal plate the uterine arteries and veins pass to and from the intervillous space. The endothelial lining of the uterine vessels ceases at the point where they terminate in the intervillous space which is lined by the syncytiotrophoblast. Portions of the stratum compactum persist and are condensed to form a series of septa, which extend from the basal plate through the thickness of the placenta and subdivide it into the lobules or cotyledons seen on the uterine surface of the detached placenta.

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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the interpretation of developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these interpretations may not reflect our current scientific understanding. (More? Embryology History)

Links: Gray's Anatomy Images

Reference: Gray, Henry. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1918.

iBook - Gray's Embryology

iTunes link | iBooks Store Description - an extract of the embryology content from Anatomy of the Human Body By Henry Gray Philadelphia: Lea & Febiger, 1918. Releases First Edition - Jan 2012 Second Edition - March 2012 Repaired formatting and image display issues related to Pad rotated display and minor editing issues. Print length 169 pages, 41.6 MB, Language English. The current website also includes numerous images from this textbook, see Anatomy of the Human Body by Henry Gray and Category:Gray's 1918 Anatomy. Note the also Historic Disclaimer.