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58-422: An organ's tissues can be broadly categorized as parenchyma , the functional tissue, and stroma , the structural tissue with supportive, connective, or ancillary functions. For example, the gland 's tissue that makes the hormones is the parenchyma , whereas the stroma includes the nerves that innervate the parenchyma, the blood vessels that oxygenate and nourish it and carry away its metabolic wastes, and

116-399: 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

174-460: A membrane or piece of connective tissue, referring to the opposing sides. The organ level of organisation in animals can be first detected in flatworms and the more derived phyla , i.e. the bilaterians . The less-advanced taxa (i.e. Placozoa , Porifera , Ctenophora and Cnidaria ) do not show consolidation of their tissues into organs. More complex animals are composed of different organs, which have evolved over time. For example,

232-456: A portion of medulla called a renal pyramid . The tumor parenchyma, of a solid tumour , is one of the two distinct compartments in a solid tumour. The parenchyma is made up of neoplastic cells . The other compartment is the stroma induced by the neoplastic cells, needed for nutritional support and waste removal. In many types of tumour, clusters of parenchymal cells are separated by a basal lamina that can sometimes be incomplete. Parenchyma

290-529: A relative of the baby. Nepalese 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 , such as Javanese and Malay, believe that

348-685: A whole, are referred to as the Organon because logic is a tool for philosophical thinking. Earlier thinkers, such as those who wrote texts in the Hippocratic corpus , generally did not believe that there were organs of the body but only different parts of the body. Some alchemists (e.g. Paracelsus ) adopted the Hermetic Qabalah assignment between the seven vital organs and the seven classical planets as follows: Chinese traditional medicine recognizes eleven organs, associated with

406-473: Is placentae , but the form placentas is more common in modern English. The placenta has evolved independently multiple times, probably starting in fish , where it originated multiple times, including the genus Poeciliopsis . Placentation has also evolved in some reptiles . The mammalian placenta evolved more than 100 million years ago and was a critical factor in the explosive diversification of placental mammals. Although all mammalian placentas have

464-429: Is also known to contain collagen proteins. Damage or trauma to the brain parenchyma often results in a loss of cognitive ability or even death. Bleeding into the parenchyma is known as intraparenchymal hemorrhage . Lung parenchyma is the substance of the lung that is involved with gas exchange and includes the pulmonary alveoli . The liver parenchyma is the functional tissue of the organ made up of around 80% of

522-461: Is critical for embryo survival. 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 . Numerous pathologies can affect the placenta. The placenta often plays an important role in various cultures , with many societies conducting rituals regarding its disposal. In the Western world , the placenta

580-411: 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 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

638-457: Is most often incinerated . Some cultures bury the placenta for various reasons. The Māori of New Zealand 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 and Costa Rica , burial of

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696-488: Is much variation in the types of cell in the parenchyma according to the species and anatomical regions. Its possible functions may include skeletal support, nutrient storage, movement, and many others. Placenta The placenta ( pl. : placentas or placentae ) is a temporary embryonic and later fetal organ that begins developing from the blastocyst shortly after implantation . It plays critical roles in facilitating nutrient, gas and waste exchange between

754-405: Is the placenta , which has evolved more than 100 times independently in vertebrates, has evolved relatively recently in some lineages, and exists in intermediate forms in extant taxa. Studies on the evolution of the placenta have identified a variety of genetic and physiological processes that contribute to the origin and evolution of organs, these include the re-purposing of existing animal tissues,

812-656: Is the bulk of functional substance in an animal organ or structure such as a tumour . In zoology , it is the tissue that fills the interior of flatworms . In botany , it is some layers in the cross-section of the leaf . The term parenchyma is Neo-Latin from the Ancient Greek word παρέγχυμα parenchyma meaning 'visceral flesh', and from παρεγχεῖν parenkhein meaning 'to pour in' from παρα- para- 'beside' + ἐν en- 'in' + χεῖν khein 'to pour'. Originally, Erasistratus and other anatomists used it for certain human tissues. Later, it

870-492: Is the tissue made up of cells and intercellular spaces that fills the interior of the body of a flatworm , which is an acoelomate . This is a spongy tissue also known as a mesenchymal tissue , in which several types of cells are lodged in their extracellular matrices . The parenchymal cells include myocytes , and many types of specialised cells. The cells are often attached to each other and also to their nearby epithelial cells mainly by gap junctions and hemidesmosomes . There

928-413: Is traditionally thought to be sterile , 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. The placenta intermediates the transfer of nutrients between mother and fetus. The perfusion of

986-404: 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 . It is proposed that melatonin plays a role as an antioxidant in the placenta. This begins at day 17–22. Placental expulsion begins as a physiological separation from the wall of

1044-428: The cancer testis antigen PAGE4 and expressed in cytotrophoblasts , CSH1 and KISS1 expressed in syncytiotrophoblasts , and PAPPA2 and PRG2 expressed in extravillous trophoblasts. 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

1102-543: The chorion and allantois . 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

1160-476: 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 cotyledons . In humans, the placenta usually has a disc shape, but size varies vastly between different mammalian species. The placenta occasionally takes

1218-486: The connective tissues that provide a suitable place for it to be situated and anchored. The main tissues that make up an organ tend to have common embryologic origins, such as arising from the same germ layer . Organs exist in most multicellular organisms . In single-celled organisms such as members of the eukaryotes , the functional analogue of an organ is known as an organelle . In plants, there are three main organs. The number of organs in any organism depends on

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1276-434: The five Chinese traditional elements and with yin and yang , as follows: The Chinese associated the five elements with the five planets (Jupiter, Mars, Venus, Saturn, and Mercury) similar to the way the classical planets were associated with different metals. The yin and yang distinction approximates the modern notion of solid and hollow organs. Parenchyma Parenchyma ( / p ə ˈ r ɛ ŋ k ɪ m ə / )

1334-416: The haruspices or the augurs in order to divine the future by their shape, dimensions or other factors. This practice remains an important ritual in some remote, tribal societies. The term "visceral" is contrasted with the term " parietal ", meaning "of or relating to the wall of a body part, organ or cavity " The two terms are often used in describing a membrane or piece of connective tissue, referring to

1392-436: The liver volume as hepatocytes . The other main type of liver cells are non-parenchymal. Non-parenchymal cells constitute 40% of the total number of liver cells but only 6.5% of its volume. The renal parenchyma is divided into two major structures: the outer renal cortex and the inner renal medulla . Grossly , these structures take the shape of 7 to 18 cone-shaped renal lobes , each containing renal cortex surrounding

1450-463: The liver , pancreas , spleen , kidneys , and adrenal glands . The hollow organs of the abdomen are the stomach , intestines , gallbladder , bladder , and rectum . In the thoracic cavity , the heart is a hollow, muscular organ. Splanchnology is the study of the viscera. The term "visceral" is contrasted with the term " parietal ", meaning "of or relating to the wall of a body part, organ or cavity ". The two terms are often used in describing

1508-548: The nervous and endocrine system both operate via a shared organ, the hypothalamus . For this reason, the two systems are combined and studied as the neuroendocrine system . The same is true for the musculoskeletal system because of the relationship between the muscular and skeletal systems . In the study of anatomy , viscera ( sg. : viscus ) refers to the internal organs of the abdominal , thoracic , and pelvic cavities . The abdominal organs may be classified as solid organs or hollow organs . The solid organs are

1566-459: The 20th century, organ transplants began to take place as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult. Both the source and method of obtaining the organ to transplant are major ethical issues to consider, and because organs as resources for transplant are always more limited than demand for them, various notions of justice, including distributive justice , are developed in

1624-439: The acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types. The study of plant organs is covered in plant morphology . Organs of plants can be divided into vegetative and reproductive. Vegetative plant organs include roots , stems , and leaves . The reproductive organs are variable. In flowering plants , they are represented by the flower , seed and fruit . In conifers ,

1682-416: The barrier function of the placenta. The placenta grows throughout pregnancy . Development of the maternal blood supply to the placenta is complete by the end of the first trimester of pregnancy week 14 (DM). 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

1740-415: The definition used. There are approxiamately 79 Organs in the human body,but it is something that is debated as not all scientist agree on what counts as an organ. Except for placozoans , multicellular animals including humans have a variety of organ systems . These specific systems are widely studied in human anatomy . The functions of these organ systems often share significant overlap. For instance,

1798-401: The ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing. The English word "organ" dates back to the twelfth century and refers to any musical instrument. By the late 14th century, the musical term's meaning had narrowed to refer specifically to the keyboard-based instrument . At

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1856-522: 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. 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, in turn, branch into cotyledon arteries . In

1914-438: 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 Transylvania and Japan , 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

1972-568: 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 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 or obesity , can increase or decrease levels of nutrient transporters in

2030-468: The liver and heart evolved in the chordates about 550-500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, molluscs, and worms about 700–650 million years ago. Given the ancient origin of most vertebrate organs, researchers have looked for model systems, where organs have evolved more recently, and ideally have evolved multiple times independently. An outstanding model for this kind of research

2088-587: The lobes get in the way of fetal presentation during labor , which is called vasa previa . 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 . Examples of proteins with elevated expression in placenta compared to other organs and tissues are PEG10 and

2146-410: The maternal-fetal barrier. Deterioration in placental functioning, referred to as placental insufficiency , 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

2204-466: The new generation of plants (see clonal colony ). Many societies have a system for organ donation , in which a living or deceased donor's organ are transplanted into a person with a failing organ. The transplantation of larger solid organs often requires immunosuppression to prevent organ rejection or graft-versus-host disease . There is considerable interest throughout the world in creating laboratory-grown or artificial organs . Beginning in

2262-428: 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. The placenta and fetus may be regarded as a foreign body inside the mother and must be protected from

2320-412: The normal immune response of the mother that would cause it to be rejected . The placenta and fetus are thus treated as sites of immune privilege , with immune tolerance . For this purpose, the placenta uses several mechanisms : 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

2378-402: The opposing sides. Aristotle used the word frequently in his philosophy, both to describe the organs of plants or animals (e.g. the roots of a tree, the heart or liver of an animal) because, in ancient Greek, the word ' organon ' means 'tool', and Aristotle believed that the organs of the body were tools for us by means of which we can do things. For similar reasons, his logical works, taken as

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2436-514: The organ that bears the reproductive structures is called a cone . In other divisions ( phyla ) of plants, the reproductive organs are called strobili , in Lycopodiophyta , or simply gametophores in mosses . Common organ system designations in plants include the differentiation of shoot and root. All parts of the plant above ground (in non- epiphytes ), including the functionally distinct leaf and flower organs, may be classified together as

2494-679: 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 that helped pave the transition from egg-laying to live-birth . The word placenta comes from the Latin 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

2552-465: 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

2610-422: The physically separate maternal and fetal circulations, and is an important endocrine organ , producing hormones that regulate both maternal and fetal physiology during pregnancy . The placenta connects to the fetus via the umbilical cord , and on the opposite aspect to the maternal uterus in a species -dependent manner. In humans, a thin layer of maternal decidual ( endometrial ) tissue comes away with

2668-428: 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 can pass through the human placenta, providing protection to the fetus in utero . This passive immunity lingers for several months after birth, providing

2726-408: 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 (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 , the dried placenta ( ziheche 紫 河 车 , literally "purple river car") is thought to be

2784-474: 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 bury girls' placentas to give

2842-435: The placenta potentially resulting in overgrowth or restricted growth of the fetus. Waste products excreted from the fetus such as urea , uric acid , and creatinine are transferred to the maternal blood by diffusion across the placenta. The placenta functions as a selective barrier between maternal and fetal cells, preventing maternal blood, proteins and microbes (including bacteria and most viruses ) from crossing

2900-421: 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 placentas probably first evolved about 150 million to 200 million years ago. The protein syncytin , found in

2958-486: The placental barrier. The trophoblast is the outer layer of cells of the blastocyst (see day 9 in Figure, above, showing the initial stages of human embryogenesis). Placental trophoblast cells have a unique genome-wide DNA methylation pattern determined by de novo methyltransferases during embryogenesis . This methylation pattern is principally required to regulate placental development and function, which in turn

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3016-430: 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 may be no medical reason to do this; on the contrary, not cutting the cord could sometimes help the baby in its adaptation to extrauterine life , for preterm infants. The placenta

3074-428: 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. Placental mammals, including humans, have a chorioallantoic placenta that forms from

3132-486: The same time, a second meaning arose, in reference to a "body part adapted to a certain function". Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal. When three or more organs are present, it is called an organ system. The adjective visceral , also splanchnic , is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by Roman pagan priests like

3190-408: The shoot organ system. The vegetative organs are essential for maintaining the life of a plant. While there can be 11 organ systems in animals, there are far fewer in plants, where some perform the vital functions, such as photosynthesis , while the reproductive organs are essential in reproduction . However, if there is asexual vegetative reproduction , the vegetative organs are those that create

3248-435: 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". 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

3306-502: 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 prostanoids 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

3364-456: Was also applied to plant tissues by Nehemiah Grew . The parenchyma is the functional parts of an organ , or of a structure such as a tumour in the body. This is in contrast to the stroma , which refers to the structural tissue of organs or of structures, namely, the connective tissues . The brain parenchyma refers to the functional tissue in the brain that is made up of the two types of brain cell , neurons and glial cells . It

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