allantois


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Related to allantois: yolk sac, urachus, Vitelline duct

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.

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]

allantois

/al·lan·to·is/ (ah-lan´to-is) a ventral outgrowth of the embryos of reptiles, birds, and mammals. In humans, it is vestigial except that its blood vessels give rise to those of the umbilical cord.

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.

allantois

[əlan′tois]
Etymology: Gk, allas, sausage, eidos, form
a tubular extension of the endoderm of the yolk sac that extends with the allantoic vessels into the connecting stalk of the embryo. In human embryos, allantoic vessels become the umbilical vessels and the chorionic villi. See also body stalk, umbilical cord, yolk sac. allantoic, adj.

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.

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]

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.

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.

allantois

a ventral outgrowth of the hindgut of the early embryo, which expands to form a large sac, filled with urine-like fluid, that fuses with the chorion to make up a major part of the placenta; vestigial in humans and some other species.

allantois adenomatous dysplasia
adenomatous nodules and plaques on the allantois of mares; usually associated with fetal disease.
References in periodicals archive ?
Virus-containing allantois liquid was taken in 15 and 30 min.
The excessive accumulation of fluid in allantoic cavity could be due to structural and functional changes in allantois chorion including its vessels with transudation and collection of fluid differing from normal allantoic fluid.
Primordial germ cells, the progenitors of gamete cells, originate in the inner lining of the yolk sac near the developing allantois (Figure 4-2).
Urine is voided either through the urachus to the allantois, or through the urethra into the amniotic cavity.
No specimen presented vestige of a membrane allantois and of a vitelline sack evident.
Eventually the allantois fuses with the chorion to form the allantochorion (also known as the chorioallantoic membrane), the membrane that becomes the fetal component of the placenta.
In eutherian mammals, the allantois is the source of blood vessels and combines with the chorion to form the chorioallantoic placenta.
The inconstant fusion of the lower limbs and their misplacement have two possible explanations: an absence of the cleavage of the common bud of the lower limbs by allantois, or an absence of the caudal extremity, which prevents the normal rotation of the lower limbs, thus leading to their fusion on the mid line.
Allantois The fetal membrane that develops from the hindgut and forms the umbilical cord and placenta in eutherian mammals.
Allantochorion The extra-embryonic membrane that forms when the allantois and chorion fuse.
DISCUSSION: The urachus developmentally is the upper part of the bladder which arises from the ventral part of the cloaca and allantois (2).