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The placenta is a temporary embryonic and later fetal
organ Organ may refer to: Biology * Organ (biology), a part of an organism Musical instruments * Organ (music), a family of keyboard musical instruments characterized by sustained tone ** Electronic organ, an electronic keyboard instrument ** Hammond ...
that begins developing from the blastocyst shortly after implantation. It plays critical roles in facilitating nutrient, gas and waste exchange between the physically separate maternal and fetal circulations, and is an important endocrine organ, producing hormones that regulate both maternal and fetal
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
during
pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...
. The placenta connects to the fetus via the umbilical cord, and on the opposite aspect to the maternal
uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
in a
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriat ...
-dependent manner. In humans, a thin layer of maternal decidual ( endometrial) tissue comes away with the placenta when it is expelled from the uterus following birth (sometimes incorrectly referred to as the 'maternal part' of the placenta). Placentas are a defining characteristic of placental mammals, but are also found in marsupials and some non-mammals with varying levels of development.
Mammalian Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...
placentas probably first evolved about 150 million to 200 million years ago. The protein syncytin, found in the outer barrier of the placenta (the syncytiotrophoblast) between mother and fetus, has a certain RNA signature in its genome that has led to the hypothesis that it originated from an ancient retrovirus: essentially a
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...
that helped pave the transition from egg-laying to live-birth. The word ''placenta'' comes from the
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through ...
word for a type of cake, from Greek πλακόεντα/πλακοῦντα ''plakóenta/plakoúnta'', accusative of πλακόεις/πλακούς ''plakóeis/plakoús'', "flat, slab-like", with reference to its round, flat appearance in humans. The classical plural is ''placentae'', but the form ''placentas'' is more common in modern English.


Phylogenetic diversity

Although all mammalian placentas have the same functions, there are important differences in structure and function in different groups of mammals. For example, human, bovine, equine and canine placentas are very different at both the gross and the microscopic levels. Placentas of these species also differ in their ability to provide maternal immunoglobulins to the fetus.


Structure

Placental mammals, including humans, have a chorioallantoic placenta that forms from the chorion and
allantois The allantois (plural ''allantoides'' or ''allantoises'') is a hollow sac-like structure filled with clear fluid that forms part of a developing amniote's conceptus (which consists of all embryonic and extraembryonic tissues). It helps the embryo ...
. In humans, the placenta averages 22 cm (9 inch) in length and 2–2.5 cm (0.8–1 inch) in thickness, with the center being the thickest, and the edges being the thinnest. It typically weighs approximately 500 grams (just over 1 lb). It has a dark reddish-blue or crimson color. It connects to the fetus by an umbilical cord of approximately 55–60 cm (22–24 inch) in length, which contains two umbilical arteries and one umbilical vein. The umbilical cord inserts into the chorionic plate (has an eccentric attachment). 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
cotyledon A cotyledon (; ; ; , gen. (), ) is a significant part of the embryo within the seed of a plant, and is defined as "the embryonic leaf in seed-bearing plants, one or more of which are the first to appear from a germinating seed." The numb ...
s. In humans, the placenta usually has a disc shape, but size varies vastly between different mammalian species. The placenta occasionally takes a form in which it comprises several distinct parts connected by blood vessels. The parts, called lobes, may number two, three, four, or more. Such placentas are described as bilobed/bilobular/bipartite, trilobed/trilobular/tripartite, and so on. If there is a clearly discernible main lobe and auxiliary lobe, the latter is called a ''succenturiate placenta''. Sometimes the blood vessels connecting the lobes get in the way of fetal presentation during labor, which is called '' vasa previa''.


Gene and protein expression

About 20,000 protein coding genes are expressed in human cells and 70% of these genes are expressed in the normal mature placenta. Some 350 of these genes are more specifically expressed in the placenta and fewer than 100 genes are highly placenta specific. The corresponding specific proteins are mainly expressed in trophoblasts and have functions related to
pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...
. Examples of proteins with elevated expression in placenta compared to other organs and tissues are PEG10 and the cancer testis antigen PAGE4 and expressed in cytotrophoblasts,
CSH1 Human placental lactogen (hPL), also called human chorionic somatomammotropin (HCS), is a polypeptide placental hormone, the human form of placental lactogen ( chorionic somatomammotropin). Its structure and function are similar to those of hum ...
and
KISS1 Kisspeptins (including kisspeptin-54 (KP-54), formerly known as metastin) are proteins encoded by the ''KISS1'' gene in humans. Kisspeptins are ligands of the G-protein coupled receptor, GPR54. ''Kiss1'' was originally identified as a human met ...
expressed in syncytiotrophoblasts, and
PAPPA2 Pappalysin-2 also known as pregnancy-associated plasma protein A2 (PAPP-A2) is a protein that in humans is encoded by the ''PAPPA2'' gene. References Further reading

* * * * * * {{gene-1-stub ...
and PRG2 expressed in extravillous trophoblasts.


Physiology


Development

The placenta begins to develop upon implantation of the blastocyst into the maternal endometrium, very early on in pregnancy at about week 4. The outer layer of the late blastocyst, is formed of trophoblasts, cells that form 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 multinucleated continuous cell layer that covers the surface of the placenta. It forms as a result of differentiation and fusion of the underlying cytotrophoblasts, a process that continues throughout placental development. The syncytiotrophoblast contributes to the barrier function of the placenta. The placenta grows throughout
pregnancy Pregnancy is the time during which one or more offspring develops ( gestates) inside a woman's uterus (womb). A multiple pregnancy involves more than one offspring, such as with twins. Pregnancy usually occurs by sexual intercourse, but ...
. Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy week 14 (DM).


Placental circulation


Maternal placental circulation

In preparation for implantation of the blastocyst, the endometrium undergoes decidualization. Spiral arteries in the decidua are remodeled so that they become less convoluted and their diameter is increased. The increased diameter and straighter flow path both act to increase maternal blood flow to the placenta. There is relatively high pressure as the maternal blood fills
intervillous space In the placenta, the intervillous space is the space between chorionic villi Chorionic villi are villi that sprout from the chorion to provide maximal contact area with maternal blood. They are an essential element in pregnancy from a histo ...
through these spiral arteries which bathe the fetal villi in blood, allowing an exchange of gases to take place. In humans and other hemochorial placentals, the maternal blood comes into direct contact with the fetal chorion, though no fluid is exchanged. As the pressure decreases between pulses, the deoxygenated blood flows back through the endometrial veins. Maternal blood flow begins between days 5–12, and is approximately 600–700 ml/min at term.


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 (plate) vessels, also fetal surface vessels are blood vessels, including both arteries and veins, that carry blood through the chorion in the fetoplacental circulation. Chorionic arteries branch off the umbilical artery, and supply the ...
. Chorionic arteries, in turn, branch into
cotyledon arteries The placenta of humans, and certain other mammals contains structures known as cotyledons, which transmit fetal blood and allow exchange of oxygen and nutrients with the maternal blood. Ruminants The Artiodactyla have a cotyledonary placenta. I ...
. In the villi, these vessels eventually branch to form an extensive arterio-capillary-venous system, bringing the fetal blood extremely close to the maternal blood; but no intermingling of fetal and maternal blood occurs ("placental barrier"). Endothelin and
prostanoid Prostanoids are active lipid mediators that regulate inflammatory response. Prostanoids are a subclass of eicosanoids consisting of the prostaglandins (mediators of inflammatory and anaphylactic reactions), the thromboxanes (mediators of vasocons ...
s cause vasoconstriction in placental arteries, while nitric oxide causes vasodilation. On the other hand, there is no neural vascular regulation, and catecholamines have only little effect. The fetoplacental circulation is vulnerable to persistent hypoxia or intermittent hypoxia and reoxygenation, which can lead to generation of excessive free radicals. This may contribute to pre-eclampsia and other
pregnancy complications Complications of pregnancy are health problems that are related to pregnancy. Complications that occur primarily during childbirth are termed obstetric labor complications, and problems that occur primarily after childbirth are termed puerperal ...
. It is proposed that melatonin plays a role as an antioxidant in the placenta. This begins at day 17–22.


Birth

Placental expulsion begins as a physiological separation from the wall of the uterus. The period from just after the child is born until just after the placenta is expelled is called the "third stage of labor". The placenta is usually expelled within 15–30 minutes of birth. Placental expulsion can be managed actively, for example by giving oxytocin via intramuscular injection followed by cord traction to assist in delivering the placenta. Alternatively, it can be managed expectantly, allowing the placenta to be expelled without medical assistance. Blood loss and the risk of postpartum bleeding may be reduced in women offered active management of the third stage of labour, however there may be adverse effects and more research is necessary. The habit is to cut the cord immediately after birth, but it is theorised that there is no medical reason to do this; on the contrary, it is theorised that not cutting the cord helps the baby in its
adaptation to extrauterine life At the end of pregnancy, the fetus must take the journey of childbirth to leave the reproductive mother. Upon its entry to the air-breathing world, the newborn must begin to adjust to life outside the uterus. This is true for all viviparous a ...
, especially in preterm infants.


Microbiome

The placenta is traditionally thought to be
sterile Sterile or sterility may refer to: *Asepsis Asepsis is the state of being free from disease-causing micro-organisms (such as pathogenic bacteria, viruses, pathogenic fungi, and parasites). There are two categories of asepsis: medical and surgi ...
, but recent research suggests that a resident, non-pathogenic, and diverse population of microorganisms may be present in healthy tissue. However, whether these microbes exist or are clinically important is highly controversial and is the subject of active research.


Functions


Nutrition and gas exchange

The placenta intermediates the transfer of nutrients between mother and fetus. 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 Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is t ...
back from the fetus to the maternal blood. Nutrient transfer to the fetus can occur via both active and passive transport. Placental nutrient metabolism was found to play a key role in limiting the transfer of some nutrients. Adverse pregnancy situations, such as those involving maternal
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
or
obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's ...
, can increase or decrease levels of nutrient transporters in the placenta potentially resulting in overgrowth or restricted growth of the fetus.


Excretion

Waste products excreted from the fetus such as urea, uric acid, and creatinine are transferred to the maternal blood by
diffusion Diffusion is the net movement of anything (for example, atoms, ions, molecules, energy) generally from a region of higher concentration to a region of lower concentration. Diffusion is driven by a gradient in Gibbs free energy or chemical ...
across the placenta.


Immunity

The placenta functions as a selective barrier between maternal and fetal cells, preventing maternal blood, proteins and microbes (including
bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were am ...
and most viruses) from crossing the maternal-fetal barrier. Deterioration in placental functioning, referred to as
placental insufficiency Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes u ...
, may be related to mother-to-child transmission of some infectious diseases. A very small number of viruses including '' rubella virus'', '' Zika virus'' and '' cytomegalovirus'' (CMV) can travel across the placental barrier, generally taking advantage of conditions at certain gestational periods as the placenta develops. CMV and Zika travel from the maternal bloodstream via placental cells to the fetal bloodstream. Beginning as early as 13 weeks of gestation, and increasing linearly, with the largest transfer occurring in the third trimester,
IgG antibodies Immunoglobulin G (Ig G) is a type of antibody. Representing approximately 75% of serum antibodies in humans, IgG is the most common type of antibody found in blood circulation. IgG molecules are created and released by plasma B cells. Each IgG a ...
can pass through the human placenta, providing protection to the fetus ''in utero''. This passive immunity lingers for several months after birth, providing the newborn with a carbon copy of the mother's long-term humoral immunity to see the infant through the crucial first months of extrauterine life. IgM antibodies, because of their larger size, cannot cross the placenta, one reason why infections acquired during pregnancy can be particularly hazardous for the fetus.


Endocrine function

* The first hormone released by the placenta is called the human chorionic gonadotropin (hCG) hormone. This is responsible for stopping the process at the end of menses when the corpus luteum ceases activity and atrophies. If hCG did not interrupt this process, it would lead to spontaneous abortion of the fetus. The corpus luteum also produces and releases progesterone and
estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...
, and hCG stimulates it to increase the amount that it releases. hCG is the indicator of pregnancy that pregnancy tests look for. These tests will work when menses has not occurred or after implantation has happened on days seven to ten. hCG may also have an anti-antibody effect, protecting it from being rejected by the mother's body. hCG also assists the male fetus by stimulating the testes to produce testosterone, which is the hormone needed to allow the sex organs of the male to grow. * Progesterone helps the embryo implant by assisting passage through the fallopian tubes. It also affects the fallopian tubes and the
uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...
by stimulating an increase in secretions necessary for fetal nutrition. Progesterone, like hCG, is necessary to prevent spontaneous abortion because it prevents contractions of the uterus and is necessary for implantation. *
Estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal ac ...
is a crucial hormone in the process of proliferation. This involves the enlargement of the breasts and uterus, allowing for growth of the fetus and production of milk. Estrogen is also responsible for increased blood supply towards the end of pregnancy through vasodilation. The levels of estrogen during pregnancy can increase so that they are thirty times what a non-pregnant woman mid-cycles estrogen level would be. * Human placental lactogen (hPL) is a hormone used in pregnancy to develop fetal metabolism and general growth and development. Human placental lactogen works with
growth hormone Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...
to stimulate Insulin-like growth factor production and regulating intermediary metabolism. In the fetus, hPL acts on lactogenic receptors to modulate embryonic development, metabolism and stimulate production of IGF, insulin, surfactant and adrenocortical hormones. hPL values increase with multiple pregnancies, intact molar pregnancy,
diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...
and
Rh incompatibility Hemolytic disease of the newborn, also known as hemolytic disease of the fetus and newborn, HDN, HDFN, or erythroblastosis foetalis, is an alloimmune condition that develops in a fetus at or around birth, when the IgG molecules (one of the five ...
. They are decreased with toxemia,
choriocarcinoma Choriocarcinoma is a malignant, trophoblastic cancer, usually of the placenta. It is characterized by early hematogenous spread to the lungs. It belongs to the malignant end of the spectrum in gestational trophoblastic disease (GTD). It is also c ...
, and
Placental insufficiency Placental insufficiency or utero-placental insufficiency is the failure of the placenta to deliver sufficient nutrients to the fetus during pregnancy, and is often a result of insufficient blood flow to the placenta. The term is also sometimes u ...
.


Immunological barrier

The placenta and fetus may be regarded as a foreign body inside the mother and must be protected from the normal
immune response An immune response is a reaction which occurs within an organism for the purpose of defending against foreign invaders. These invaders include a wide variety of different microorganisms including viruses, bacteria, parasites, and fungi which coul ...
of the mother that would cause it to be
rejected ''Rejected'' is an animated film directed by Don Hertzfeldt that was released in 2000. It was nominated for an Academy Award for Best Animated Short Film the following year at the 73rd Academy Awards, and received 27 awards from film festivals ...
. The placenta and fetus are thus treated as sites of immune privilege, with immune tolerance. For this purpose, the placenta uses several mechanisms : *It 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. *There is presence of small lymphocytic suppressor cells in the fetus that inhibit maternal cytotoxic T cells by inhibiting the response to interleukin 2. However, the placental barrier is not the sole means of evading the immune system, as foreign fetal cells also persist in the maternal circulation, on the other side of the placental barrier.


Other

The placenta also provides a reservoir of blood for the fetus, delivering blood to it in case of hypotension and vice versa, comparable to a
capacitor A capacitor is a device that stores electrical energy in an electric field by virtue of accumulating electric charges on two close surfaces insulated from each other. It is a passive electronic component with two terminals. The effect of ...
.


Clinical significance

Numerous pathologies can affect the placenta. * Placenta accreta, when the placenta implants too deeply, all the way to the actual muscle of uterine wall (without penetrating it) * Placenta praevia, when the placement of the placenta is too close to or blocks the cervix *
Placental abruption Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dang ...
, premature detachment of the placenta *
Placentitis Placentitis is an inflammation of the placenta. The main forms of placentitis are: *Villitis, inflammation of chorionic villi. *Intervillositis, inflammation of the intervillous space. It may be caused by vertically transmitted infections. ...
, inflammation of the placenta, such as by
TORCH infections A vertically transmitted infection is an infection caused by pathogenic bacteria or viruses that use mother-to-child transmission, that is, transmission directly from the mother to an embryo, fetus, or baby during pregnancy or childbirth. It ca ...
.


Society and culture

The placenta often plays an important role in various
culture Culture () is an umbrella term which encompasses the social behavior, institutions, and norms found in human societies, as well as the knowledge, beliefs, arts, laws, customs, capabilities, and habits of the individuals in these groups ...
s, with many societies conducting rituals regarding its disposal. In the
Western world The Western world, also known as the West, primarily refers to the various nations and states in the regions of Europe, North America, and Oceania.
, the placenta is most often incinerated. Some cultures bury the placenta for various reasons. The
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...
of
New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island coun ...
traditionally bury the placenta from a newborn child to emphasize the relationship between humans and the earth. Likewise, the Navajo bury the placenta and umbilical cord at a specially chosen site, particularly if the baby dies during birth. In
Cambodia Cambodia (; also Kampuchea ; km, កម្ពុជា, UNGEGN: ), officially the Kingdom of Cambodia, is a country located in the southern portion of the Indochinese Peninsula in Southeast Asia, spanning an area of , bordered by Thailand ...
and Costa Rica, burial of the placenta is believed to protect and ensure the health of the baby and the mother. 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. The placenta is believed by some communities to have power over the lives of the baby or its parents. The Kwakiutl of
British Columbia British Columbia (commonly abbreviated as BC) is the westernmost province of Canada, situated between the Pacific Ocean and the Rocky Mountains. It has a diverse geography, with rugged landscapes that include rocky coastlines, sandy beaches, for ...
bury girls' placentas to give the girl skill in digging clams, and expose boys' placentas to ravens to encourage future
prophet In religion, a prophet or prophetess is an individual who is regarded as being in contact with a divine being and is said to speak on behalf of that being, serving as an intermediary with humanity by delivering messages or teachings from the ...
ic visions. In
Turkey Turkey ( tr, Türkiye ), officially the Republic of Türkiye ( tr, Türkiye Cumhuriyeti, links=no ), is a transcontinental country located mainly on the Anatolian Peninsula in Western Asia, with a small portion on the Balkan Peninsula ...
, the proper disposal of the placenta and umbilical cord is believed to promote devoutness in the child later in life. In
Transylvania Transylvania ( ro, Ardeal or ; hu, Erdély; german: Siebenbürgen) is a historical and cultural region in Central Europe, encompassing central Romania. To the east and south its natural border is the Carpathian Mountains, and to the west the A ...
, and
Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the n ...
, interaction with a disposed placenta is thought to influence the parents' future fertility. Several cultures believe the placenta to be or have been alive, often a relative of the baby.
Nepal Nepal (; ne, नेपाल ), formerly the Federal Democratic Republic of Nepal ( ne, सङ्घीय लोकतान्त्रिक गणतन्त्र नेपाल ), is a landlocked country in South Asia. It is ma ...
ese think of the placenta as a friend of the baby; the orang Asli and Malay populations in Malay Peninsula regard it as the baby's older sibling. Native Hawaiians believe that the placenta is a part of the baby, and traditionally plant it with a tree that can then grow alongside the child. Various cultures in
Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania between the Indian and Pacific oceans. It consists of over 17,000 islands, including Sumatra, Java, Sulawesi, and parts of Borneo and New Gui ...
, such as Javanese and Malay, believe that the placenta has a spirit and needs to be buried outside the family house. Some Malays would bury the baby's placenta with a
pencil A pencil () is a writing or drawing implement with a solid pigment core in a protective casing that reduces the risk of core breakage, and keeps it from marking the user's hand. Pencils create marks by physical abrasion, leaving a tra ...
(if it is a boy) or a needle and thread (if it is a girl). In some cultures, the placenta is eaten, a practice known as placentophagy. In some eastern cultures, such as
China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...
, the dried placenta (''ziheche'' , literally "purple river car") is thought to be a healthful restorative and is sometimes used in preparations of traditional Chinese medicine and various health products. The practice of
human placentophagy Human placentophagy, or consumption of the placenta, is defined as "the ingestion of a human placenta postpartum, at any time, by any person, either in raw or altered (e.g., cooked, dried, steeped in liquid) form". While there are several anecdotes ...
has become a more recent trend in western cultures and is not without controversy; its practice being considered cannibalism is debated. Some cultures have
alternative uses for placenta The placenta is an organ which links the fetus to the mother in mammals for the transfer of oxygen and nutrients to the fetus and fetal waste products to the mother. Many species of mammals consume their placentas. Placentas are consumed in some ...
that include the manufacturing of cosmetics, pharmaceuticals and food.


Additional images

File:Gray30.png, Fetus of about 8 weeks, enclosed in the amnion. Magnified a little over two diameters. File:Placenta with fetal membranes.jpg, Placenta with attached fetal membranes, ruptured at the margin at the left in the image File:CMV placentitis1.jpg,
Micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a m ...
of a placental
infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...
( CMV placentitis) File:CMV placentitis2.jpg, Micrograph of CMV placentitis File:Placenta vasculature 3D power doppler 00001.gif, A 3D Power Doppler image of vasculature in 20-week placenta File:2910 The Placenta-02.jpg, Schematic view of the placenta File:Human placenta 01.JPG, Maternal side of a whole human placenta, just after birth File:Human placenta 02.JPG, Fetal side of same placenta File:Fetal side close-up of freshly delivered placenta.jpeg, Close-up of umbilical attachment to fetal side of freshly delivered placenta File:Placenta weight by gestational age.svg, Placenta weight by gestational age File:Ziheche.jpg, ''Ziheche'' (紫河车), dried human placenta used in traditional Chinese medicine


See also

*
Choriovitelline placenta A choriovitelline placenta is a placenta formed by the yolk sac and chorion. In a choriovitelline placenta, the yolk sac fuses with the chorion and, subsequently, wrinkles develop that hold the embryo to the uterine wall, thus forming the choriovite ...
* Caul *
Zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicell ...
*
Pregnancy in fish Pregnancy has been traditionally defined as the period of time eggs are incubated in the body after egg-sperm union. Although the term often refers to placental mammals, it has also been used in the titles of many international, peer-reviewed, sc ...


References


External links


The placenta-specific proteome
a
the Human Protein Atlas


gynob.com, with quotes from Williams Obstetrics, 18th Edition, F. Gary Cunningham, M.D., Paul C. MacDonald, M.D., Norman F. Grant, M.D., Appleton & Lange, Publishers. {{Authority control Vertebrate developmental biology Embryology of cardiovascular system Organs (anatomy) Reproductive system Microbiomes Human female endocrine system