Дамушы ұрықты қорғаушы мембрана

Innermost membranous sac that surrounds and protects a developing embryo
the fictional alien species

The amnion (: amnions or amnia) is a membrane that closely covers human and various other embryos when they first form. It fills with amniotic fluid, which causes the amnion to expand and become the amniotic sac that provides a protective environment for the developing embryo. The amnion, along with the chorion, the yolk sac and the allantois protect the embryo. In birds, reptiles and monotremes, the protective sac is enclosed in a shell. In marsupials and placental mammals, it is enclosed in a uterus. The amnion is a feature of the vertebrate clade Amniota, which includes reptiles, birds, and mammals. Amphibians and fish lack the amnion and thus are anamniotes (non amniotes). The amnion stems from the extra embryonic somatic mesoderm on the outer side and the extra embryonic ectoderm or trophoblast on the inner side.

Traditionally, the term amnion has been assumed to derive from Ancient Greek ἀμνίον : amníon, 'little lamb', diminutive of ἀμνός : amnós, 'lamb'. It is cognate with the English verb 'yean', bring forth young (usually lambs). However, this etymology is perhaps incorrect as the term may actually refer to an ancient Greek goddess of childbirth worshipped in Amnisos on the island of Crete

In the human embryo, the earliest stages of the formation of the amnion have not been observed; in the youngest embryo that 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. 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. When first formed, the amnion is in contact with the body of the embryo, but about the fourth or fifth week amniotic fluid (also called liquor amnii) begins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the chorion's inner surface, so that the extra embryonic part of the coelom is obliterated. The amniotic fluid 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. The amniotic fluid allows 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.

Extra amniotic pregnancy is a rare condition that results from a rupture of the amnion, leading to development of the fetus within the extraembryonic coelom.

The amniotic membrane is used as a biological dressing to heal incurable wounds. For this purpose, the placenta in cesarean delivery is collected and under aseptic conditions, the amniotic membrane is separated and packaged and sold commercially. In valid commercial products to prevent transmission of viral infections such as HIV and hepatitis, the donor's blood (mother) is tested. Products usually pass the sterility and endotoxin test in accordance with the rules of the Food and Drug Administration of the country of manufacture.