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Encyclopedia > Amnion
Amnion
Surface view of embryo of Hylobates concolor.
Human fetus, enclosed in the amnion.
Gray's subject #12 56
MeSH Amnion
For the alien race in Stephen Donaldson's The Gap Cycle, see Amnion (Gap Cycle).

The amnion is a membranous sac that surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, which are hence called “Amniota”; but not in amphibia and fish, which are consequently termed “Anamnia”. The primary function of this is the protection of the embryo for its future development into a fetus and eventually an animal. Image File history File links Gray14. ... Image File history File links Gray30. ... Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. ... Stephen Reeder Donaldson (born May 13, 1947) is an American fantasy and science fiction novelist. ... The Gap Cycle is a science fiction story, told in a series of 5 books, written by Stephen Donaldson The Gap into Conflict: The Real Story, Bantam/Spectra, 1991 The Gap into Vision: Forbidden Knowledge, Bantam/Spectra, 1991 The Gap into Power: A Dark and Hungry God Arises, Bantam/Spectra... The Amnion are s fictional alien species in Stephen Donaldsons The Gap Cycle. ... For other uses, see Embryo (disambiguation). ... Orders  Crocodilia - Crocodilians scary crocodiles. ... For other meanings of bird, see bird (disambiguation). ... Orders Subclass Monotremata Monotremata Subclass Marsupialia Didelphimorphia Paucituberculata Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Subclass Placentalia Xenarthra Dermoptera Desmostylia Scandentia Primates Rodentia Lagomorpha Insectivora Chiroptera Pholidota Carnivora Perissodactyla Artiodactyla Cetacea Afrosoricida Macroscelidea Tubulidentata Hyracoidea Proboscidea Sirenia The mammals are the class of vertebrate animals primarily characterized by the presence of mammary... Extant subgroups Synapsida     Mammalia (mammals) Sauropsida    Anapsida        Testudines (turtles)    Diapsida        Lepidosauria           Squamata (lizards and snakes)           Sphenodontida (tuatara)        Archosauria           Crocodilia (crocodiles and alligators)           Aves (birds) The amniotes are a group of vertebrates, comprising the mammals, birds, and various other groups collectively referred to as reptiles. ... For other uses, see Amphibian (disambiguation). ... For other uses, see Fish (disambiguation). ...

Contents

In humans

In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac, and appears in the inner cell-mass as a cavity. This cavity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk—the continuity between the roof and floor being established at the margin of the embryonic disk. Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the mesodermal lining of the chorion. The mesoderm is one of the three germ layers in the early developing embryo, the other two layers being the ectoderm and the endoderm. ... When the lateral mesoderm splits into two layers, the outer (or somatic) one becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure. ...


When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the coelom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of pregnancy, after which it diminishes somewhat; at the end of pregnancy it amounts to about 1 liter. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than two percent solids, consisting of urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentary canal. For the entertainment company see Chorion (company) The chorion surrounds the embryo and other membranes. ... Coelom with Dermal Tissue One of the primary ways zoologists group animals has to do with the presence or absence of a coelom and how it is formed. ... A representation of the 3D structure of myoglobin showing coloured alpha helices. ... This article is about sugar as food and as an important and widely-traded commodity. ...


In reptiles, birds, and many mammals

In reptiles, birds, and many mammals the amnion is developed in the following manner


At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place. The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation. ...


This, the amniotic fold, first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and gradually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. amniotic sac The amniotic sac is a tough but thin transparent pair of membranes, which hold a developing embryo (and later fetus) until shortly before birth. ...


After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa.


The space between the amnion and the serosa constitutes the extra-embryonic celom, and for a time communicates with the embryonic celom. The Amnion then is transported across the mesoderm to relieve further protection from such harmful chemicals as, zytoisn, poitan and the most dangerous of all, the exploatan.


Additional images

See also

A drawing of the amniotic sac from Grays Anatomy. ...

External links

This article was originally based on an entry from a public domain edition of Gray's Anatomy. As such, some of the information contained herein may be outdated. Please edit the article if this is the case, and feel free to remove this notice when it is no longer relevant. For the similarly named institution in Chestnut Hill, see Boston College. ... The public domain comprises the body of all creative works and other knowledge—writing, artwork, music, science, inventions, and others—in which no person or organization has any proprietary interest. ... An illustration from the 1918 edition Henry Grays Anatomy of the Human Body (or Grays Anatomy as it has more commonly become known) is an anatomy textbook widely regarded as a classic work on human anatomy. ...

The placenta (Latin for cake, referencing its appearance in humans) is an ephemeral organ present in placental vertebrates, such as eutherial mammals and sharks during gestation (pregnancy). ... Decidua is the term for the uterine lining (endometrium) during a pregnancy. ... Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. ... Chorionic villi are villi that sprout from the chorion, in order to give a maximum area of contact with the maternal blood. ... The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal tissues and open into the maternal bloodvessels, with the result that the spaces in the trophoblastic network are filled with maternal blood; these spaces communicate freely with one... The gestational sac is the only available intrauterine structure that can be used to determine if an intrauterine pregnancy (IUP) exists, until the embryo is identified. ... A drawing of the amniotic sac from Grays Anatomy. ... amniotic sac The amniotic sac is a tough but thin transparent pair of membranes, which hold a developing embryo (and later fetus) until shortly before birth. ... For the entertainment company see Chorion (company) The chorion surrounds the embryo and other membranes. ... An Introduction to Histogenesis Histogenesis is defined as the formation of tissues and organs from undifferentiated cells (Encarta Dictionary). ... Programmed cell death (PCD) is the deliberate suicide of an unwanted cell in a multicellular organism. ... Mouse embryonic stem cells. ... The cells that give rise to the gametes are often set aside during cleavage. ... Organogenesis is a stage of animal development where the ectoderm, endoderm, and mesoderm are formed. ... The vertebrate limb arises out of a general morphogenetic area called a limb field. ... In embryology, the limb bud is a structure formed by the developing limb, derived from lateral plate mesoderm[citation needed]. It is intimately related with the apical ectodermal ridge, which secretes factors inducing the initial differentiation of the limb bud. ... The Apical Ectodermal Ridge (AER) is a critical component in vertebrate limb development. ... Transverse section showing the lens and the optic cup. ... Cutaneous structures arise from the epidermis and include a variety of features such as hair, feathers, claws and nails. ... The heart is the first functional organ in a vertebrate embryo. ... In prenatal development, the urinary and reproductive organs are developed from the intermediate mesoderm. ...

  Results from FactBites:
 
Vitro cellular interaction with amnion membrane substrate - Patent 4446234 (4617 words)
The amnion membrane which is the subject of this invention is obtained from mammalian placenta by dissection from the chorion membrane by known methods; the integrity of the isolated amnion is then preferably verified by permeability and morphology studies.
The amnion membranes useful in the practice of the present invention are derived from mammalian placenta, preferably after sufficient gestation to allow differentiation of the chorion and amnion layers in the fetal membrane, typically four to five months in humans.
The amnion membrane 1 or 1a and the diagnostic apparatus of the invention are useful in in vitro assay methods for studying the interaction of a wide variety of cell types with the basement membrane surface.
Gray, Henry. 1918. Anatomy of the Human Body. Page 56 (578 words)
In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac (Figs.
This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the celom is obliterated.
In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection or folding upward of the somatopleure takes place.
  More results at FactBites »

 
 

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