amnion


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Related to amnion: yolk sac, amnion nodosum

amnion

the innermost of two membranes (see also chorion) enclosing an embryonic reptile, bird, or mammal

Amnion

A thin, cellular, extraembryonic membrane forming a closed sac surrounding the embryo in all reptiles, birds, and mammals. It is present only in these forms; the collective term amniotes is applied to these animals. The amnion contains a serous fluid in which the embryo is immersed. See Amniota

Typically, the amnion wall is a tough, transparent, nerve-free, and nonvascular membrane consisting of two layers of cells: an inner, single-cell-thick layer of ectodermal epithelium and an outer covering of mesodermal, connective, and specialized smooth muscular tissue. Early after the formation of the amnion, waves of contraction of the muscles pass over the amniotic sac and produce a characteristic rocking of the embryo. See Germ layers

The major function of the amnion and its fluid is to protect the delicate embryo. Thus, developmental stages of terrestrial animals are provided with the same type of cushioning against mechanical shock as is provided by the water environment of aquatic forms. See Fetal membrane

Amnion

 

one of the embryonic membranes found in a number of vertebrates (reptiles, birds, mammals) and invertebrates. Depending on whether the amnion is present or absent, two groups are distinguished—the Amniota (or higher) and the Anamnia (or lower). The amnion develops around the embryo in the form of folds of the extraembryonic ectoderm and the peritoneum parietal of the lateral plates of the mesoderm—that is, the external and median germ layers. After accretion of the edges of the folds, the embryo is within two membranes—the inner membranes, or amnion, and the external, or serous, membrane (called the chorion in mammals). In reptiles the amnion is without vessels; in birds and mammals it develops vessels and contractile muscular elements. The amniotic cavity becomes filled with a large amount of exudate from the vessels—the so-called amniotic, or fetal, fluid which protects the embryo from mechanical injury and desiccation. The fluid contains organic compounds (proteins, urea, sugar, hormones) and also inorganic salts. The amnion bursts during parturition and the amniotic fluid escapes; the remnants of the amnion on the body of the newborn individual are called the rubashechka (“little shirt”). The blastoderm in insects, scorpions, nemerteans, and sea urchins is also called the amnion.

amnion

[′am·nē‚än]
(embryology)
A thin extraembryonic membrane forming a closed sac around the embryo in birds, reptiles, and mammals.
References in periodicals archive ?
The amnion was separated and washed seven times with phosphate-buffered saline (PBS) supplemented with 100 IU/ml penicillin and 100 ug/ml streptomycin to remove blood.
Lim, "Human amnion epithelial cells mediate lung repair by directly modulating macrophage recruitment and polarization," Cell Transplantation, vol.
Immunohistochemical analysis showed that epithelial cells of amnion membrane, endothelial cells of blood vessels and fibroblast cells of the GDM group expressed high levels of CD44 (Fig.
First, the intrinsic model, described by Streeter in 1930 [5], which suggests the existence of an early embryolesion with alterations of the germinal disc that would produce an inflammatory response of the adjacent amnions and that would then develop a fibrous band.
Keeping in mind the adhesive properties of the amnion, the membrane was not sutured.
Signs of placentitis were revealed in 46.6% of all placentas studied, and in 40% of amnion samples.
Amniotic fluid is the watery liquid surrounding and cushioning a growing fetus within the amnion. It allows the fetus to move freely without the walls of the uterus being too tight against its body.
More recently, research in the rapidly expanding field of regenerative sports medicine has been turning up promising uses for this vital, nourishing organ in the form of amniotic membrane (or "amnion") injections.
Placental teratoma is a rare tumor its usual location is between amnion and chorion.
By the time the amniotic sac is visible, the embryo can be readily identified; the absence of an embryo, or "empty amnion sign," is highly specific for a failed pregnancy (Figure 6).
* Presented Grafix pharmacoeconomic and scientific studies at the Symposium for Advanced Wound Care--demonstrating statistically significant economic benefits of wound closure and showing a quantitative comparison of wound relevant pharmacological parameters between cryopreserved and non-cryopreserved human amnion membranes;
Amnion zarinin epitelizasyonu baslatici, enflamasyon ve anjiogenezisi inhibe edici, agriyi azaltici, antiadeziv ve bakteriostatik etkileri vardir.