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 ?
When implantation has occurred, and the syncytiotrophoblast (the part of the trophoblast that first invades the endometrium) grows larger and establishes quasi-connections with the mother's uterine blood vessels, the business of the inner cell mass's differentiation through gastrulation can take place with the assurance that the structures now being produced--the amnion, the umbilical vessels, and the placenta proper--can perform their proper functions.
BioCover is the first membrane composed of donated amnion tissue for use as a wound covering in the treatment of gingival recession (receding gums).
Evaluation of the cranial base in amnion rupture sequence involving the anterior neural tube: implications regarding recurrence risk.
The amnion can crack spontaneously, but can also tear after amniocentesis - in which a needle is used to extract amniotic fluid to test for genetic diseases - or foetal surgery.
You did not establish or maintain standard operating procedures for the following critical operations: obtain placenta from donors; donor eligibility screening; procedures for storage, processing of placentas to obtain amnion tissue and cells, and disposition of the placentas; testing the placentas for contaminants; screening of the subjects' suitability in accepting the amnion tissue and cell implants for a non-homologous use; implantation procedures; and subject follow-up for adverse experiences subsequent to the implantation.
Be sure you're visualizing the separate amnion and not mistaking it for skin.
Necrosis in any of the umbilical vessels or amnion was strongly associated with the presence of T.
The core technology behind the company's current product offering is placental tissue of which the amnion is the innermost layer of the amniotic sac and is composed of collagen types IV, V and VII and bioactive factors including fibronectin and laminins which allow for cellular adhesion of gingival cells.
Transport of blood and blood products, biomaterials and tissue samples from patients and biological materials such as the cornea, the amnion to and from other medical centers and laboratory reagents, drugs to and from the hospital and imports (inversely) the results of diagnostic tests ordered.
attained significant increase of biomechanical strength, enzymatic resistance, transparency and less wrinkling of amnion used for surface reconstruction of the cornea.
In summary, up to now, the placental membrane was a site looked at mainly for features of acute inflammation (chorioamnionitis), meconium, hemosiderin, amnion nodosum, and decidual arteriolopathy.
Amniotic fluid is the nourishing and protecting liquid contained by the amnion of a pregnant woman.