Definition of amnion in English:


nounPlural amnia, Plural amnions

  • The innermost membrane that encloses the embryo of a mammal, bird, or reptile.

    • ‘Meconium changes were separated into 4 groups: pigment in the amnion only, pigment in the amnion and decidua, a green - stained umbilical cord, and meconium-associated vascular necrosis of large fetal vessels.’
    • ‘The one that is visible at the earliest stage of development is the amnion.’
    • ‘The middle part of the streak gives rise mainly to lateral plate mesoderm, while the posterior part of the streak provides the extra-embryonic mesoderm of the amnion, visceral yolk sac, and allantois.’
    • ‘Inside the egg are a series of fluid-filled membranes which permit the embryo to survive: the amnion, allantois, yolk sac, and chorion.’
    • ‘Care was exercised not to separate the amniotic sac into its components, the chorion and amnion.’
    • ‘They described primitive cells found in a part of the placenta called the amnion, which they coaxed into forming a variety of cell types and which look very similar to sought-after embryonic stem cells.’
    • ‘The amnion is derived from the embryo and forms as early as eight days after fertilization, when the fate of cells has yet to be determined, and serves to protect the developing fetus.’
    • ‘Human amnion has been suggested for use as a biologic burn dressing, especially in developing countries.’
    • ‘The amniotes are a monophyletic group of vertebrates, comprising reptiles, birds, and mammals, that develops in its embryonic life the envelope called amnion.’
    • ‘We're talking about things like the amnion, the chorion, the allantoic sac, the placenta, the umbilical cord, if those words sound familiar to you.’
    • ‘Amniotes are characterized by the presence of an amniote egg, that is an egg with a hard outer covering that could be laid on land and that contained a membrane, the amnion, that surrounded the embryo in a fluid-filled sac.’
    • ‘Associated with deposition of meconium pigment is a typical degenerative change of the amnionic epithelium consisting initially of heaping up of the cells, forming a multilayered amnion.’


Mid 17th century: from Greek, ‘caul’, diminutive of amnos ‘lamb’.