allantois

Information about allantois

Diagram illustrating early formation of allantois and differentiation of body-stalk.
Sectional plan of the gravid uterus in the third and fourth month.
subject #12 54
Days16
Precursoryolk sac
Gives rise toUmbilical cord
MeSH Allantois
Dorlands/Elsevier a_24/12121253
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 allontois, along with the amnion and chorion (other embryonic membranes), identify humans as amniotes, along with reptiles, dinosaurs, birds, and other mammals.

Function

This sac-like structure is primarily involved in respiration 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

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.[1]
  • 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, a vestigial structure with an unknown function.

Pathology

A patent allantois can result in urachal cyst.

Etymology

The word comes from the Greek word for sausage,[2] which the allantois resembles.

Additional images


Section through the embryo.

Diagram showing later stage of allantoic development with commencing constriction of the yolk-sac.

Diagram showing the expansion of amnion and delimitation of the umbilicus.

Model of human embryo 1.3 mm. long.

Tail end of human embryo from fifteen to eighteen days old.

Cloaca of human embryo from twenty-five to twenty-seven days old.

Tail end of human embryo twenty-five to twenty-nine days old.

Tail end of human embryo thirty-two to thirty-three days old.

Opened uterus with cat fetus in midgestation: 1 umbilicus, 2 amnion, 3 allantois, 4 Yolk sac, 5 developing marginal hematoma, 6 maternal part of placenta (endometrium)


References

1. ^ Downs, K.M. 1998. "The Murine Allantois". Current Topics in Developmental Biology vol. 39, pp 1-33.
2. ^ a_24/12121170 at Dorland's Medical Dictionary

External links

 •  • [ e]
Human development of embryo and development of fetus (some dates are approximate - see Carnegie stages and a timeline)
Week 1Zygote - Morula - Blastomere - Blastula/Blastosphere/Blastocyst/Blastocoele - Inner cell mass
Week 2Bilaminar disc (Hypoblast, Epiblast) - Archenteron/Primitive streak
Week 3 (Trilaminar embryo)Primitive knot/Blastopore - Primitive groove - Gastrula/Gastrulation
Germ layer: Ectoderm (Neuroectoderm) - Endoderm - Mesoderm (Chorda-, Paraxial, Intermediate, Lateral plate) - Splanchnopleure/Somatopleure
Somite/Somitomere (Sclerotome, Myotome, Dermatome)
Uterine supportAllantois - Trophoblast (Cytotrophoblast, Syncytiotrophoblast, Gestational sac) - Yolk sac - Vitelline duct - Placenta - Umbilical cord (Umbilical artery, Umbilical vein, Wharton's jelly) - Amniotic sac (Amnion, Chorion) - Decidua - Decidual cells - Intervillous space - Chorionic villi
Branchial regionBranchial arch (1st/Meckel's cartilage, 2nd)/Branchial pouch - Cervical sinus - Lateral lingual swelling - Tuberculum impar - Frontonasal prominence - Olfactory pit - Nasal processes - Globular process - Primitive palate
Histogenesis and organogenesisGlands: Thyroglossal duct
Limb development: Limb bud - Apical ectodermal ridge/AER
Embryology is the study of the development of an embryo. An embryo is defined as any vertebrate in a stage before birth or hatching. Embryology refers to the development of the egg cell (zygote) after fertilization and the differentiation of cells into tissues and organs.
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The yolk sac is the first element seen in the gestational sac during pregnancy, usually at 5 weeks gestation.

It is a critical landmark, identifying a true gestation sac.

It is quite echogenic (light) to ultrasound, and reliably seen early.
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In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. It normally contains three vessels, two arteries (Umbilical artery) and one vein (Umbilical vein), buried within Wharton's jelly, for the exchange of nutrient- and
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Medical Subject Headings (MeSH) is a huge controlled vocabulary (or metadata system) for the purpose of indexing journal articles and books in the life sciences. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed
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Elsevier, the world's largest publisher of medical and scientific literature, forms part of the Reed Elsevier group. Based in Amsterdam, the company has substantial operations in the UK, USA and elsewhere.
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Conceptus (latin is conceptio, derivatives of zygote) denotes the embryo and its adnexa (appendages or adjunct parts) or associated membranes (i.e. the products of conception) The conceptus includes all structures that develop from the zygote, both embryonic and extraembryonic.
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Please [improve the article] or discuss this issue on the talk page. This article has been tagged since December 2006.
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For the entertainment company see Chorion (company).
The chorion surrounds the embryo and other membranes. It consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the somatic mesoderm; with this latter the
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Amniota
Haeckel, 1866

Living subgroups

See text

The amniotes are a group of tetrapod vertebrates that include the Synapsida (mammals and mammal-like reptiles) and Sauropsida (reptiles and dinosaurs, including birds).
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Sauropsida*
Goodrich, 1916

Subclasses
  • Anapsida
  • Diapsida
Synonyms
  • Reptilia Laurenti, 1768
Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class
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Dinosauria *
Owen, 1842

Orders & Suborders
  • Ornithischia
  • Cerapoda
  • Thyreophora
  • Saurischia

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Aves
Linnaeus, 1758

Orders

About two dozen - see section below

Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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In animal physiology, respiration is the transport of oxygen from the ambient air to the tissue cells and the transport of carbon dioxide in the opposite direction. This is in contrast to the biochemical definition of respiration, which refers to cellular respiration
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Excretion is the process of eliminating waste products of metabolism and other non-useful materials.[1] It is an essential process in all forms of life.

In single-celled organisms, waste products are discharged directly through the surface of the cell.
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The blood vessels are part of the cardiovascular system and function to transport blood throughout the body. The most important types, arteries and veins, carry blood away from or towards the heart, respectively.
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Sauropsida*
Goodrich, 1916

Subclasses
  • Anapsida
  • Diapsida
Synonyms
  • Reptilia Laurenti, 1768
Reptiles are tetrapods and amniotes, animals whose embryos are surrounded by an amniotic membrane, and members of the class
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Aves
Linnaeus, 1758

Orders

About two dozen - see section below

Birds (class Aves) are bipedal, warm-blooded, egg-laying vertebrate animals.
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2, −1
(neutral oxide)
Electronegativity 3.44 (Pauling scale)
Ionization energies
(more) 1st: 1313.9 kJmol−1
2nd: 3388.3 kJmol−1
3rd: 5300.5 kJmol−1

Atomic radius 60 pm
Atomic radius (calc.
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eggshell is a term for the outer covering of a hard-shelled egg, and some forms of eggs with soft outer coats.

The generalized eggshell structure, which varies widely among species, is a protein matrix lined with mineral crystals, usually of a calcium compound such as
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Monotremata
C.L. Bonaparte, 1837

Families

†Kollikodontidae
Ornithorhynchidae
Tachyglossidae
†Steropodontidae
Monotremes (from the Greek monos 'single' + trema
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Mammalia
Linnaeus, 1758

Subclasses & Infraclasses
  • Subclass †Allotheria*
  • Subclass Prototheria
  • Subclass Theria

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Marsupialia
Illiger, 1811

Orders
  • Didelphimorphia
  • Paucituberculata
  • Microbiotheria
  • Dasyuromorphia
  • Peramelemorphia
  • Notoryctemorphia
  • Diprotodontia
  • Sparassodonta (extinct)
  • Yalkaparidontia (extinct)
Marsupials
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For the entertainment company see Chorion (company).
The chorion surrounds the embryo and other membranes. It consists of two layers: an outer formed by the primitive ectoderm or trophoblast, and an inner by the somatic mesoderm; with this latter the
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bandicoot is any of about 20 species of small to medium-sized, terrestrial marsupial omnivores in the order Peramelemorphia. The word bandicoot is an anglicised form of the Telugu word pandi-kokku
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Eutheria

Orders[1]
  • Bobolestes
  • Eomaia
  • Maelestes
  • Montanalestes
  • Murtoilestes
  • Prokennalestes
  • Placentalia
  • Superorder

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In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. It normally contains three vessels, two arteries (Umbilical artery) and one vein (Umbilical vein), buried within Wharton's jelly, for the exchange of nutrient- and
..... Click the link for more information.
MOUSE was founded in 1997 by entrepreneur Andrew Rasiej and Founding Executive Director Sarah Holloway. Along with leaders from the "high tech" community in New York City, MOUSE spearheaded the process of wiring public schools for Internet access in New York City.
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The germ layer mesoderm forms in the embryos of animals more complex than cnidarians, making them triploblastic. Mesoderm forms during gastrulation when some of the cells migrating inward to form the endoderm form an additional layer between the endoderm and the ectoderm.
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