allantois

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allantois

 [ah-lan´to-is]
a small sausage-shaped outpouching from the caudal wall of the yolk sac of the early embryo, associated with early blood formation and development of the urinary bladder; its blood vessels become the umbilical arteries and veins. adj., adj allanto´ic.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

al·lan·to·is

(ă-lan'tō-is),
A fetal membrane developing from the hindgut (or yolk sac, in humans). In humans it becomes a fibrous cord, the urachus; externally, in other mammals, it contributes to the formation of the umbilical cord and placenta; in birds and reptiles, it lies close beneath the porous shell and serves as an organ of respiration.
Synonym(s): allantoid membrane
[allanto- + G. eidos, appearance]
Farlex Partner Medical Dictionary © Farlex 2012

allantois

(ə-lăn′tō-ĭs)
n. pl. allantoides (ăl′ən-tō′ĭ-dēz′)
A membranous sac that develops from the posterior part of the digestive tract in the embryos of mammals, birds, and reptiles. It is important in the formation of the umbilical cord and placenta in mammals. Also called allantoid.

al′lan·to′ic (ăl′ən-tō′ĭk) adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

allantois

An extraembryonic membranous sac found in a developing animal conceptus, which is comprised of all embryonic and extraembryonic tissues. It is intimately involved in gas and liquid waste exchange, as well as erythropoiesis; it gives rise to the foetal umbilical arteries and vein and contributes to the formation of the urinary bladder.
Segen's Medical Dictionary. © 2012 Farlex, Inc. All rights reserved.

al·lan·to·is

(ă-lan'tō-is)
A fetal membrane developing from the hindgut (or umbilical vesicle, in humans). In humans it becomes a fibrous cord, the urachus; externally, in mammals, it contributes to the formation of the umbilical cord and placenta.
Synonym(s): allantoid membrane.
[allanto- + G. eidos, appearance]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

allantois

A membranous sac that develops from the hindgut in the EMBRYO and takes part in the formation of the umbilical cord and the PLACENTA.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

allantois

a membranous growth from the central side of the hind gut of the developing vertebrate embryo that extends outside the embryo proper and is covered by a layer of connective tissue containing many blood vessels. In birds and reptiles the allantois acts as a respiratory surface with the allantoic cavity (see Fig. 30 being used for the storage of excretory materials. In placental mammals the allantoic blood vessels carry blood to and from the PLACENTA for respiration, nutrition and excretion. In all groups most of the allantois is detached at birth.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005