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14-September-2008 18:02:48 - Placenta This article may require cleanup to meet 's quality standards. Please improve this article if you can. June 2007 Placenta Placenta Precursor decidua basalis, chorion frondosum Dorlands/Elsevier p_22/12643330 The placenta is an ephemeral organ present in placental vertebrates, such as eutherial mammals and sharks during gestation pregnancy. The term placenta comes from the Latin for cake, from Greek plakoenta, accusative of plakoeis - πλακοείς, flat12, referencing its appearance in humans. Protherial egg-laying and metatherial marsupial mammals do not produce a placenta. The placenta develops from the same sperm and egg cells that form the fetus, and functions as a foetomaternal organ with two components, the foetal part Chorion frondosum, and the maternal part Decidua basalis. Contents 1 Structure 2 Development 3 Placental circulation 3.1 Maternal placental circulation 3.2 Fetoplacental circulation 4 Functions 4.1 Nutrition 4.2 Metabolic and endocrine activity 4.3 Parasitic cloaking from immune system of mother 5 Birth 5.1 Non-humans 6 Pathology 7 Cultural practices and beliefs 8 Additional images 9 See also 10 References 11 External links Structure In humans, the placenta averages 22 cm 8.66 in. in length and 2-2.5 cm 0.79-0.98 in. in thickness. It typically weighs approximately 500 grams 17.64 oz.. It has a dark reddish/blue or maroon color. It connects to the fetus by an umbilical cord of approximately 55-60 cm 21.65-23.62 in. in length that contains two arteries and one vein.3 The umbilical cord inserts into the chorionic plate. Vessels branch out over the surface of the placenta and further divide to form a network covered by a thin layer of cells. This results in the formation of villous tree structures. On the maternal side, these villous tree structures are grouped into lobules called cotelydons. In humans the placenta usually has a disc shape but different mammalian species have widely varying shapes.4 Development The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium. The outer layer of the blastocyst becomes the trophoblast which forms the outer layer of the placenta. This outer layer is divided into two further layers; the underlying cytotrophoblast layer and the overlying syncytiotrophoblast layer. The syncytiotrophoblast is a multinucleate continuous cell layer which covers the surface of the placenta. It forms as a result of differentiation and fusion of the underlying cytotrophoblast cells, a process which continues throughout placental development. The syncytiotrophoblast otherwise known as syncytium, thereby contributes to the barrier function of the placenta. The placenta grows throughout pregnancy. Development of the maternal blood supply to the placenta is suggested to be complete by the end of the first trimester of pregnancy approximately 12-13 weeks. Placental circulation Maternal placental circulation In preparation for implantation, the uterine endometrium undergoes 'decidualisation'. Spiral arteries in the decidua are remodelled so that they become less convoluted and their diameter is increased. This increases maternal blood flow to the placenta and also decreases resistance so that shear stress is reduced. The relatively high pressure as the maternal blood enters the intervillous space through these spiral arteries bathes the villi in blood. An exchange of gases takes place. As the pressure decreases, the deoxygenated blood flows back through the endometrial veins. Fetoplacental circulation Deoxygenated fetal blood passes through umbilical arteries to the placenta. At the junction of umbilical cord and placenta, the umbilical arteries branch radially to form chorionic arteries. Chorionic arteries also branch before they enter into the villi. In the villi, they form an extensive arteriocapillary venous system, bringing the fetal blood extremely close to the maternal blood; but no intermingling of fetal and maternal blood occurs placental barrier5. Functions Nutrition The perfusion of the intervillous spaces of the placenta with maternal blood allows the transfer of nutrients and oxygen from the mother to the fetus and the transfer of waste products and carbon dioxide back from the fetus to the mother. Metabolic and endocrine activity In addition to the transfer of gases and nutrients, the placenta also has metabolic and endocrine activity. It produces, among other hormones, progesterone, which is important in maintaining the pregnancy; somatomammotropin also known as placental lactogen, which acts to increase the amount of glucose and lipids in the maternal blood; estrogen; relaxin, and beta human chorionic gonadotrophin beta-hCG. This results in increased transfer of these nutrients to the fetus and is also the main cause of the increased blood sugar levels seen in pregnancy. This hormone beta-hCG ensures that progesterone and oestrogen are secreted; progesterone and oestrogen thicken and maintain the uterine lining as well as inhibit the production and release of more eggs. However after about 2 months the placenta takes on the role of producing progesterone and therefore beta-hCG is no longer needed. Beta-hCG is excreted in urine and this is what pregnancy tests detect. It also produces insulin-like growth factors IGFs. Parasitic cloaking from immune system of mother To hide itself from attack by the mother's immune system, the placenta secretes Neurokinin B containing phosphocholine molecules. This is the same mechanism used by parasitic nematodes to avoid detection by the immune system of their host.6 Birth When the fetus is born, its placenta begins a physiological separation for spontaneous expulsion afterwards and for this reason is also called the afterbirth. The umbilical cord is routinely clamped and severed prior to the delivery of the placenta, often within seconds or minutes of birth, a medical protocol known as 'active management of third stage' which has been called into question by advocates of natural birth and 'passive management of third stage'7 The site of the former umbilical cord attachment in the center of the front of the abdomen is known as the umbilicus, navel, or belly-button. Modern obstetric practice has decreased maternal death rates enormously. The addition of active management of the third stage of labor is a major contributor towards this. It involves giving oxytocin via IM injection, followed by cord traction to assist in delivering the placenta. Premature cord traction can pull the placenta before it has naturally detached from the uterine wall, resulting in hemorrhage. The BMJ summarized the Cochrane group metanalysis 2000 of the benefits of active third stage as follows: One systematic review found that active management of the third stage of labour, consisting of controlled cord traction, early cord clamping plus drainage, and a prophylactic oxytocic agent, reduced postpartum haemorrhage of 500 or 1000 mL or greater and related morbidities including mean blood loss, postpartum haemoglobin less than 9 g/dL, blood transfusion, need for supplemental iron postpartum, and length of third stage of labour. Although active management increased adverse effects such as nausea, vomiting, and headache, one RCT identified by the review found that women were less likely to be dissatisfied when their third stage of labour was actively managed.1 Risks of retained placenta include hemorrhage and infection. If the placenta fails to deliver in 30 minutes in a hospital environment, manual extraction may be required if heavy ongoing bleeding occurs, and very rarely a curettage is necessary to ensure that no remnants of the placenta remain in rare conditions with very adherent placenta placenta accreta. However, in birth centers and attended home birth environments, it is common for licensed care providers to wait for the placenta's birth up to 2 hours in some instances. Non-humans or section by expanding it. Further information might be found on the talk page or at requests for expansion. April 2008 In most mammalian species, the mother bites through the cord and consumes the placenta, primarily for the benefit of prostaglandin on the uterus after birth. This is known as placentophagy. However, it has been observed in zoology that chimpanzees, with which humans share 99% of genetic material, apply themselves to nurturing their offspring, and keep the fetus, cord, and placenta intact until the cord dries and detaches the next day. Top: Human placenta shown a few minutes after birth. The side shown faces the baby with the umbilical cord top right. The white fringe surrounding the bottom is the remnants of the amniotic sac. Bottom: A different placenta displays side that connects to the uterine wall. Top: Human placenta shown a few minutes after birth. The side shown faces the baby with the umbilical cord top right. The white fringe surrounding the bottom is the remnants of the amniotic sac. Bottom: A different placenta displays side that connects to the uterine wall. Pathology See: Placenta accreta Placenta praevia Placental abruption Cultural practices and beliefs The placenta often plays an important role in various human cultures, with many societies conducting rituals regarding its disposal. In the Western world, the placenta is most often incinerated.8 Some cultures bury the placenta for various reasons. The MÄ?ori of New Zealand traditionally bury the placenta from a newborn child to emphasize the relationship between humans and the earth.9 Similarly, the Navajo bury the placenta and umbilical cord at a specially-chosen site,10 particularly if the baby dies during birth.11 In Cambodia and Costa Rica, burial of the placenta is believed to protect and ensure the health of the baby and the mother.12 If a mother dies in childbirth, the Aymara of Bolivia bury the placenta in a secret place so that the mother's spirit will not return to claim her baby's life.13 The placenta is believed by some communities to have power over the lives of the baby or its parents. The Kwakiutl of British Columbia bury girls' placentas to give the girl skill in digging clams, and expose boys' placentas to ravens to encourage future prophetic visions. In Turkey, the proper disposal of the placenta and umbilical cord is believed to promote devoutness in the child later in life. In Ukraine, Transylvania, and Japan, interaction with a disposed placenta is thought to influence the parents' future fertility. The ancient Egyptians believed that the placenta was imbued with magical powers.12 In fact, the placenta of the pharoah was placed on a pole and carried into battle. This is history's first flag. http://www.psychohistory.com/htm/eln04f_footnotestrauma.html Several cultures believe the placenta to be or have been alive, often a relative of the baby. Nepalese think of the placenta as a friend of the baby's; Malaysian Orang Asli regard it as the baby's older sibling. The Ibo of Nigeria consider the placenta the deceased twin of the baby, and conduct full funeral rites for it.12 Native Hawaiians believe that the placenta is a part of the baby, and traditionally plant it with a tree which can then grow alongside the child.8 In some cultures, the placenta is eaten, a practice known as placentophagy. Additional images Fetus of about 8 weeks, enclosed in the amnion. Magnified a little over two diameters. Picture of freshly delivered placenta and umbillical cord See also Embryo Partuition Uterus References ^ Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus ^ Online Etymology Dictionary ^ Examination of the placenta ^ http://www.vivo.colostate.edu/hbooks/pathphys/reprod/placenta/structure.html Placental Structure and Classification ^ Placental blood circulation ^ Placenta 'fools body's defences'. BBC News 2007-11-10. ^ http:www.sarahjbuckley.com/articles/leaving-well-alone.htm ^ a b Why eat a placenta?, BBC 2006-04-18. Retrieved on 2008-01-08. ^ Metge, Joan. 2005. Working in/Playing with three languages: English, Te Reo Maori, and Maori Bod Language. In Sites N.S vol. 2, No 2:83-90. ^ Francisco, Edna 2004-12-03. Bridging the Cultural Divide in Medicine. Minority Scientists Network. Retrieved on 2008-01-07. ^ Shepardson, Mary 1978. Changes in Navajo Mortuary Practices and Beliefs. American Indian Quarterly. University of Nebraska Press. Retrieved on 2008-01-07. ^ a b c Buckley, Sarah J.. Placenta Rituals and Folklore from around the World. Mothering. Retrieved on 2008-01-07. ^ Davenport, Ann June 2005. The Love Offer. Johns Hopkins Magazine. Retrieved on 2008-01-07. Marsupial at Bartleby.com About Marsupials at KnowYourSTO.com Fetus at humpath.com External links Wikimedia Commons has media related to: Placenta Additional Human placenta photography 2 v d e Developmental biology Human embryogenesis development of embryo and development of fetus some dates are approximate - see Carnegie stages and a timeline Week 1 Fertilization - Egg activation - Zygote - Cleavage - Morula - Blastula Blastomere - Blastocyst - Inner cell mass Week 2 Bilaminar disc Hypoblast, Epiblast Week 3 Trilaminar embryo, germ layers Archenteron/Primitive streak Primitive pit, Primitive knot/Blastopore, Primitive groove - Gastrula/Gastrulation - Regional specification Ectoderm: Surface ectoderm - Neuroectoderm - Somatopleure - Neurulation - Neural crest Endoderm: Splanchnopleure Mesoderm: Chorda- - Paraxial Somite/Somitomere/Sclerotome/Myotome/Dermatome - Intermediate - Lateral plate Intraembryonic coelom, Splanchnopleure/Somatopleure Extraembryonic/uterus Trophoblast Cytotrophoblast, Syncytiotrophoblast Blastocoele - Yolk sack/exocoelomic cavity - Heuser's membrane - Extraembryonic coelom - Vitelline duct Umbilical cord Umbilical artery, Umbilical vein, Wharton's jelly - Allantois Placenta - Decidua Decidual cells - Chorionic villi/Intervillous space - Gestational sac Amnion/Amniotic sac/Amniotic cavity, Chorion Histogenesis Programmed cell death Apoptosis - Stem cells - Germ line development Organogenesis Limb development: Limb bud - Apical ectodermal ridge/AER other structures: Eye development - Cutaneous structure development - Heart development - Development of the urinary and reproductive organs v d e Human anatomy, endocrine system: endocrine glands Hypothalamic/ pituitary axes Thyroid axis Thyroid gland Parafollicular cell, Thyroid epithelial cell, Thyroid isthmus, Lobes of thyroid gland, Pyramid of thyroid Parathyroid gland Oxyphil cell, Chief cell Adrenal axis Adrenal gland Gonadal axis Testes - Ovaries - Corpus luteum Pineal gland Pinealocyte Islets of pancreas Alpha cell - Beta cell - Delta cell - PP cell - Epsilon cell Retrieved from http://en..org/wiki/Placenta Categories: Developmental biology | Embryology | Greek loanwordsHidden categories: Cleanup from June 2007 | All pages needing cleanup | Articles to be expanded since April 2008 | All articles to be expanded Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages العربية Aymar БългарÑ?ки Català Česky Dansk Deutsch Þ‹Þ¨ÞˆÞ¬Þ€Þ¨Þ„Þ¦Þ?Þ° Emilià n e rumagnòl Español Esperanto Ù?ارسی Français हिनà¥?दी Bahasa Indonesia Ã?slenska Italiano עברית Latina Lietuvių Magyar Nederlands 日本語 ‪Norsk bokmÃ¥l‬ Polski Português РуÑ?Ñ?кий Shqip Simple English СрпÑ?ки / Srpski Basa Sunda Suomi Svenska తెలà±?à°—à±? Türkçe ä¸æ–‡ This page was last modified on 11 September 2008, at 07:0
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