Infobox Embryology
Name = Allantois
Latin =
GraySubject = 12
GrayPage = 54

Caption = Diagram illustrating early formation of allantois and differentiation of body-stalk.

Caption2 = Sectional plan of the gravid uterus in the third and fourth month.
System =
CarnegieStage =
Days = 16
Precursor = yolk sac
GivesRiseTo = Umbilical cord
MeshName = Allantois
MeshNumber = A10.615.284.147
DorlandsPre = a_24
DorlandsSuf = 12121253

Allantois (plural "allantoides" or "allantoises") is a part of a developing animal conceptus (which consists of all embryonic and extra-embryonic tissues). It helps the embryo exchange gases and handle liquid waste.

The allantois, along with the amnion and chorion (other embryonic membranes), identify humans as amniotes, along with reptiles, dinosaurs, birds, and other mammals.


This sac-like structure is primarily involved in nutrition and excretion, and is webbed with blood vessels.

The function of the allantois is to collect liquid waste from the embryo, as well as to exchange gases used by the embryo.

In reptiles, birds, and monotremes

The structure first evolved in reptiles and birds as a reservoir for nitrogenous waste, but also as a means for oxygenation of the embryo.

Oxygen is absorbed by the allantois through the egg shell. The allantois functions similarly in monotremes, which are egg-laying mammals.

In most marsupials

In most marsupials, the allantois is avascular, having no blood vessels, but still serves the purpose of storing nitrogenous (N2) waste.

Also, most marsupial allantoises do not fuse with the chorion. An exception is the allantois of the bandicoot, which has a vasculature, and fuses with the chorion.

In placental mammals (Eutheria)

In placental mammals, the allantois is part of and forms an axis for the development of the umbilical cord.

* The mouse allantois consists of mesodermal tissue, which undergoes vasculogenesis to form the mature umbilical artery and vein. [Downs, K.M. 1998. "The Murine Allantois". "Current Topics in Developmental Biology" vol. 39, pp 1-33.]

* The human allantois is an endodermal evagination of the developing hindgut which becomes surrounded by the mesodermal connecting stalk. The connecting stalk forms the umbilical vasculature. These endodermal and mesodermal tissues together form the human umbilical cord. The allantois later becomes the urachus, which removes nitrogenous waste from the fetal bladder [First AID for the USMLE Step 1 2008] .


A patent allantois can result in urachal cyst.


The word comes from the Greek word for sausage, which the allantois resembles.



External links

* [ at University of Texas - Arlington]

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Look at other dictionaries:

  • Allantois — Al*lan to*is, Allantoid Al*lan toid, ] n.. (Anat.) A membranous appendage of the embryos of mammals, birds, and reptiles, in mammals serving to connect the fetus with the parent; the urinary vesicle. [1913 Webster] …   The Collaborative International Dictionary of English

  • Allantŏis — (gr.), Harnhaut, eine längliche, wurstförmige, dünne Blase, die während der 2 ersten Monate nach der Befruchtung bei dem aus dem Ei sich entwickelnden Fötus der Menschen u. Thiere zwischen 2 anderen Eihäuten (dem Chorion u. Amnion) in der Nähe… …   Pierer's Universal-Lexikon

  • Allantōis — (griech., Harnhaut, Harnsack), eine der Hüllen, die den Embryo der Reptilien, Vögel und Sänger umgeben. Sie entsteht als eine Ausstülpung des Darmes, wächst in Form einer gestielten Blase aus der Bauchhöhle des Embryos hervor und bis zur innern… …   Meyers Großes Konversations-Lexikon

  • Allantois — Allantōis (grch.), Harnhaut, eine Hülle des Embryos der höhern Wirbeltiere (Allantoidĕa: Säugetiere, Vögel, Reptilien), vermittelt bei Reptilien und Vögeln die Atmung, bei den Säugetieren durch Bildung des Mutterkuchens auch noch die …   Kleines Konversations-Lexikon

  • Allantoïs — Allantoïs, bei dem Fötus mehrerer Säugethiere eine zarte, weiße Haut zwischen dem Chorium und Amnium, in Form einer wurstförmigen Blase, durch die Nabelschnur mittelst der Blasenschnur mit der Harnblase zusammenhängend. In ihr findet sich die… …   Herders Conversations-Lexikon

  • Allantois — ⇒ Embryonalhüllen …   Deutsch wörterbuch der biologie

  • allantois — [ə lan′tō is] n. pl. allantoides [al΄ən tō′ə dēz΄] [ModL < Gr allantoeidēs, sausage shaped < allas, sausage (prob. < dial. allē, garlic, via Oscan * allo < L alium, allium) + eidēs, OID] a membranous pouch with a rich blood supply in… …   English World dictionary

  • Allantois — Eröffnete Gebärmutter einer Katze mit einem Fötus in der Mitte der Trächtigkeit. 1 Nabel, 2 Amnion, 3 Allantois, 4 Dottersack, 5 sich entwickelndes Randhämatom, 6 mütterlicher Teil der Plazenta. Allantois (gr. ho allás, allántos: „Die… …   Deutsch Wikipedia

  • allantois — A fetal membrane developing from the hindgut (or yolk sac, in humans). In humans it is vestigial; externally, in mammals, it contributes to the formation of the umbilical cord and placenta; in birds and reptiles, it lies close beneath the porous… …   Medical dictionary

  • allantois — /euh lan toh is, toys/, n. Embryol., Zool. a vascular, extraembryonic membrane of birds, reptiles, and certain mammals that develops as a sac or diverticulum from the ventral wall of the hindgut. [1640 50; < NL < Gk allantoeidés, wrongly taken… …   Universalium

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