fetal membrane

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Fetal membrane

One of the membranous structures which surround the embryo during its developmental period. Since such membranes are external to the embryo proper, they are called extraembryonic membranes. They function in the embryo's protection, nutrition, respiration, and excretion.

There are four fetal membranes—the amnion, chorion, yolk sac, and allantois. In the course of development, the chorion becomes the outermost, and the amnion the innermost, membrane surrounding the developing embryo. As the allantois increases in size, it expands and becomes closely associated, if not fused, with the chorion. The two membranes together are known as the chorioallantoic membrane.

The amniotic cavity within which the embryo is enclosed becomes filled with an aqueous fluid which gives osmotic and physical protection to the embryo during the remainder of its fetal existence. Smooth muscle fibers in the amnion spontaneously contract and gently rock the embryo before it develops the capacity for spontaneous movement.

As the stored nutrients of the yolk are depleted during development, the yolk sac gradually decreases in size and is eventually incorporated into the midgut of the embryo. The yolk sac in the nonyolky eggs of placental mammals is vestigial. It has evolutionary but essentially no functional significance.

At the time of birth or hatching, the embryo becomes completely separated from the amnion and chorion and from the major portion of the allantois. The proximal portion of the latter remains within the embryo, however, as the urinary bladder. See Allantois, Amnion, Chorion, Yolk sac

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.

fetal membrane

[′fēd·əl ′mem‚brān]
Any one of the membranous structures which surround the embryo during its development period. Also known as extraembryonic membrane.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
Caption: Figure 1: Morphology of placental components: (a, b) placental tissue (villi): Tr: trophoblast; Vess: vessels; Mes: mesenchyme; (c) fetal membranes: Am: amniotic membrane; Ch: chorionic membrane; (d) surface cells of amniotic epithelium; (e) cross-section of the umbilical cord; (f) umbilical cord tissue.
Strauss, "Premature rupture of the fetal membranes," The New England Journal of Medicine, vol.
Therefore, the present study aimed to evaluate and compare the antibacterial properties of the two amniotic and chorionic fetal membranes in vitro.
As mentioned in an earlier section of this chapter, the fetal membranes do not invade the endometrial mucosa in swine, sheep, cattle, and horses.
The differentiation of organs and the growth and structure of the placenta, fetal membranes, uterus, and the fetus itself are described.
A second expert had stated that the only reasonable cause for the rupture of her fetal membrane was illness from the S.
Similar results were found in a recent study with fetal membranes [77], which however, did not analyze reflected and placental amnions separately.
Premature rupture of fetal membranes can occur spontaneously or in association with a surgical procedure.
Nava et al., "Fetal membrane cells for treatment of steroid-refractory acute graft-versus-host disease," Stem Cells, vol.
To test this hypothesis, fetal membrane specimens were obtained from 29 women who were diagnosed with preterm PROM.
During pregnancy, defects in the fetal membrane can lead to the leakage of amniotic fluid, resulting in premature labor or termination of the pregnancy.
Factors that predispose to premature rupture of the fetal membrane. Obstet Gynecol 1982; 60:93-8.