血液漿膜の、絨毛膜血腫性の

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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/04/10 18:21:26」(JST)

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Placentation

Placentation resulting from cleavage at various gestational ages
Latin	placentatio

In biology, placentation refers to the formation, type and structure, or arrangement of placentas. The function of placentation is to transfer nutrients from maternal tissue to a growing embryo. Placentation is best known in pregnant female mammals (eutheria), but also occurs in other animals, eggs (yolk sac placentation) and flowering plants.

Placentation in mammals

Further information: Placenta

In placental mammals, the placenta forms after the embryo implants into the wall of the uterus. The developing fetus is connected to it via an umbilical cord. Animal placentas are classified based on the number of tissues separating the maternal from the fetal blood. The placentation types found in animals are:

endotheliochorial placentation (e.g. in most carnivores like cats and dogs)
epitheliochorial placentation (e.g. in ruminants, horses, whales, lower primates)
hemochorial placentation (e.g. in higher order primates, including humans, and also in guinea pigs, rabbits, mice, and rats)^[1]

In hemochorial placentation maternal blood comes in direct contact with the fetal chorion, which it does not in the other two types.^[2] It may avail for more efficient transfer of nutrients etc., but is also more challenging for the systems of gestational immune tolerance to avoid rejection of the fetus.^[3]

During pregnancy, placentation is the formation and growth of the placenta inside the uterus. It occurs after the implantation of the embryo into the uterine wall and involves the remodeling of blood vessels in order to supply the needed amount of blood. In humans, placentation takes place 7–8 days after fertilization.

In humans, the placenta develops in the following manner. Chorionic villi (from the embryo) on the embryonic pole grow, forming chorion frondosum. Villi on the opposite side (abembryonic pole) degenerate and form the chorion laeve (or chorionic laevae), a smooth surface. The endometrium (from the mother) over the chorion frondosum (this part of the endometrium is called the decidua basalis) forms the decidual plate. The decidual plate is tightly attached to the chorion frondosum and goes on to form the actual placenta. Endometrium on the opposite side to the decidua basalis is the decidua parietalis. This fuses with the chorion laevae, thus filling up the uterine cavity. ^[4]

In the case of twins, dichorionic placentation refers to the presence of two placentas (in all dizygotic and some monozygotic twins). Monochorionic placentation occurs when monozygotic twins develop with only one placenta and bears a higher risk of complications during pregnancy. Abnormal placentation can lead to an early termination of pregnancy, for example in pre-eclampsia.

Placentation in plants

In flowering plants, placentation occurs where the ovules are attached inside the ovary.^[5] The ovules inside a flower's ovary (which later become the seeds inside a fruit) are attached via funiculi, the plant part equivalent to an umbilical cord. The part of the ovary where the funiculus attaches is referred to as the placenta.

In botany, the term placentation most commonly refers to the arrangement of placentas inside a flower or fruit. Plant placentation types include:

Basal placentation: The placenta is at the base (bottom) of the ovary. Simple or compound carpel.
Apical placentation: The placenta is at the apex (top) of the ovary. Simple or compound carpel.
Parietal placentation: The placentas are in the ovary wall within a non-sectioned ovary. Compound carpel.
Axile placentation: The ovary is sectioned by radial spokes with placentas in separate locules. Compound carpel.
Free or central placentation: The placentas are in a central column within a non-sectioned ovary. Compound carpel.
Marginal placentation: There is only one elongated placenta on one side of the ovary , as ovules are attached at the fusion line of the Carple's Margins . This is conspicuous in legumes. Simple carpel.

References

^ Claim for guinea pigs, rabbits, mice, and rats taken from: Thornburg KL, Faber JJ (October 1976). "The steady state concentration gradients of an electron-dense marker (ferritin in the three-layered hemochorial placenta of the rabbit". J. Clin. Invest. 58 (4): 912–25. doi:10.1172/JCI108544. PMC 333254. PMID 965495.
^ thefreedictionary.com > hemochorial placenta Citing: Dorland's Medical Dictionary for Health Consumers. Copyright 2007 by Saunders
^ Elliot, M.; Crespi, B. (2006). "Placental invasiveness mediates the evolution of hybrid inviability in mammals". The American naturalist 168 (1): 114–120. doi:10.1086/505162. PMID 16874618. edit
^ T.W. Sadler, Langman's Medical Embryology, 11th edition, Lippincott & Wilkins
^ "Flowers" At: Botany Online At: University of Hamburg Department of Biology. (see External links below).

External links

Flowers At: How to Identify Plants At: Contents At: Homepage: Botany Online - The Internet Hypertextbook At: B-Online At: teaching stuff At: Department of Biology (This page in English) At: Fachbereich Biologie

English Journal

IFPA award in placentology lecture: Phylogenomic origins and evolution of the mammalian placenta.

Wildman DE1.
Placenta.Placenta.2016 Apr 6. pii: S0143-4004(16)30055-8. doi: 10.1016/j.placenta.2016.04.004. [Epub ahead of print]
The placenta has had the most dynamic evolutionary history of all mammalian organs. It has undergone massive shifts in anatomy, physiology, and the way in which uterine and fetal tissue interact with one another during pregnancy. The human placenta is arguably the best studied amongst mammals, yet m
PMID 27105828

Oxidative stress and the evolutionary origins of preeclampsia.

Elliot MG1.
Journal of reproductive immunology.J Reprod Immunol.2016 Apr;114:75-80. doi: 10.1016/j.jri.2016.02.003. Epub 2016 Mar 4.
In this speculative paper, I consider the relationship between oxidative stress and the evolution of placentation in eutherian mammals. I argue that epitheliochorial placentation, in which fetal tissues remain separated from maternal blood throughout gestation, has evolved as a protective mechanism
PMID 26995772

Differential Spatiotemporal Patterns of Galectin Expression are a Hallmark of Endotheliochorial Placentation.

Conrad ML1, Freitag N1, Diessler ME2, Hernandez R2, Barrientos G1,3, Rose M1, Casas LA4, Barbeito CG2,3, Blois SM1.
American journal of reproductive immunology (New York, N.Y. : 1989).Am J Reprod Immunol.2016 Mar;75(3):317-25. doi: 10.1111/aji.12452. Epub 2015 Nov 21.
PROBLEM: Galectins influence the progress of pregnancy by regulating key processes associated with embryo-maternal cross talk, including angiogenesis and placentation. Galectin family members exert multiple roles in the context of hemochorial and epitheliochorial placentation; however, the galectin
PMID 26589652