In a multicellular

organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...

, an organ is a collection of tissues joined in a structural unit to serve a common function. In the

hierarchy of life Biological organization is the organization of complex biological structures and systems that define life using a reductionistic approach. The traditional hierarchy, as detailed below, extends from atoms to biospheres. The higher levels of t ...

, an organ lies between tissue and an

organ system An organ system is a biological system consisting of a group of organ (biology), organs that work together to perform one or more bodily functions. Each organ has a specialized role in an organism body, and is made up of distinct Tissue (biolog ...

. Tissues are formed from same type

cells Cell most often refers to: * Cell (biology), the functional basic unit of life * Cellphone, a phone connected to a cellular network * Clandestine cell, a penetration-resistant form of a secret or outlawed organization * Electrochemical cell, a d ...

to act together in a function. Tissues of different types combine to form an organ which has a specific function. The intestinal wall for example is formed by

epithelial tissue Epithelium or epithelial tissue is a thin, continuous, protective layer of cells with little extracellular matrix. An example is the epidermis, the outermost layer of the skin. Epithelial ( mesothelial) tissues line the outer surfaces of man ...

and

smooth muscle tissue Smooth muscle is one of the three major types of vertebrate muscle tissue, the others being skeletal muscle, skeletal and cardiac muscle. It can also be found in invertebrates and is controlled by the autonomic nervous system. It is non-striated ...

. Two or more organs working together in the execution of a specific body function form an organ system, also called a

biological system A biological system is a complex Biological network inference, network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different structures depending on what the system is ...

or body system. An organ's tissues can be broadly categorized as

parenchyma upright=1.6, Lung parenchyma showing damage due to large subpleural bullae. Parenchyma () is the bulk of functional substance in an animal organ such as the brain or lungs, or a structure such as a tumour. In zoology, it is the tissue that ...

, the functional tissue, and stroma, the structural tissue with supportive, connective, or

ancillary {{Short pages monitor The study of plant organs is covered in

plant morphology Phytomorphology is the study of the physical form and external structure of plants.Raven, P. H., R. F. Evert, & S. E. Eichhorn. ''Biology of Plants'', 7th ed., page 9. (New York: W. H. Freeman, 2005). . This is usually considered distinct from pl ...

. Organs of

plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...

s can be divided into vegetative and reproductive. Vegetative plant organs include

root In vascular plants, the roots are the plant organ, organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often bel ...

s, stems, and

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

. The reproductive organs are variable. In

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...

s, they are represented by the

flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...

seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...

and

fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...

. In

conifers Conifers () are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All e ...

, the organ that bears the reproductive structures is called a

cone In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the '' apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines ...

. In other divisions (

phyla Phyla, the plural of ''phylum'', may refer to: * Phylum, a biological taxon between Kingdom and Class * by analogy, in linguistics, a large division of possibly related languages, or a major language family which is not subordinate to another Phy ...

) of plants, the reproductive organs are called

strobili A strobilus (: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to the woo ...

, in ''

Lycopodiophyta The lycophytes, when broadly circumscribed, are a group of vascular plants that include the clubmosses. They are sometimes placed in a division Lycopodiophyta or Lycophyta or in a subdivision Lycopodiophytina. They are one of the oldest lineag ...

'', or simply gametophores in

moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...

es. Common organ system designations in plants include the differentiation of shoot and root. All parts of the plant above ground (in non-

epiphyte An epiphyte is a plant or plant-like organism that grows on the surface of another plant and derives its moisture and nutrients from the air, rain, water (in marine environments) or from debris accumulating around it. The plants on which epiphyt ...

s), including the functionally distinct leaf and flower organs, may be classified together as 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 Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...

, while the reproductive organs are essential in

reproduction Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: Asexual reproduction, asexual and Sexual ...

. However, if there is

asexual Asexual or Asexuals may refer to: *Asexual reproduction **Asexual reproduction in starfish *Asexuality, the lack of sexual attraction to anyone or lack of interest in or desire for sexual activity. **Gray asexuality, the spectrum between asexualit ...

vegetative reproduction Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is a form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or specializ ...

, the vegetative organs are those that create the new generation of plants (see

clonal colony A clonal colony or genet is a group of genetically identical individuals, such as plants, fungi, or bacteria, that have grown in a given location, all originating vegetatively, not sexually, from a single ancestor. In plants, an individual in ...

Society and culture

Many societies have a system for

organ donation Organ donation is the process when a person authorizes an organ (anatomy), organ of their own to be removed and organ transplantation, transplanted to another person, #Legislation and global perspectives, legally, either by consent while the d ...

, 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 Immunosuppression is a reduction of the activation or efficacy of the immune system. Some portions of the immune system itself have immunosuppressive effects on other parts of the immune system, and immunosuppression may occur as an adverse react ...

to prevent

organ rejection Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

graft-versus-host disease Graft-versus-host disease (GvHD) is a syndrome, characterized by inflammation in different organs. GvHD is commonly associated with bone marrow transplants and stem cell transplants. White blood cells of the donor's immune system which rema ...

. There is considerable interest throughout the world in creating laboratory-grown or

artificial organ An artificial organ is a human-made organ device or Tissue (biology), tissue that is Implant (medicine), implanted or integrated into a humaninterfacing with living tissueto replace a natural Organ (anatomy), organ, to duplicate or augment a spec ...

Organ transplants

Beginning in the 20th century,

organ transplants Organ transplantation is a medical procedure in which an organ is removed from one body and placed in the body of a recipient, to replace a damaged or missing organ. The donor and recipient may be at the same location, or organs may be trans ...

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 Distributive justice concerns the Social justice, socially just Resource allocation, allocation of resources, goods, opportunity in a society. It is concerned with how to allocate resources fairly among members of a society, taking into account fa ...

, are developed in the ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing. Animal donor organs and tissue have been subjects of study since the 1960s, and some xenotransplant tissues, particularly heart valves, have been commonly utilized. Xenotransplant has the potential to address the critical shortage in organ grafts. The science behind enotransplanttrials has advanced considerably and more human clinical trials utilizing porcine xenografts are quickly approaching.

History

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 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 In a multicellular organism, an organ is a collection of Tissue (biology), tissues joined in a structural unit to serve a common function. In the biological organization, hierarchy of life, an organ lies between Tissue (biology), tissue and an o ...

'', also ''

splanchnic Splanchnic is usually used to describe organs in the abdominal cavity. It is used when describing: * Splanchnic tissue * Splanchnic organs - including the stomach, small intestine, large intestine, pancreas, spleen, liver, and may also include the ...

'', is used for anything pertaining to the internal organs. Historically, viscera of animals were examined by

Roman Roman or Romans most often refers to: *Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD *Roman people, the people of Roman civilization *Epistle to the Romans, shortened to Romans, a letter w ...

pagan

priest A priest is a religious leader authorized to perform the sacred rituals of a religion, especially as a mediatory agent between humans and one or more deity, deities. They also have the authority or power to administer religious rites; in parti ...

s like the

haruspices In the religion of ancient Rome, a haruspex was a person trained to practise a form of divination called haruspicy, the inspection of the entrails of sacrificed animals, especially the livers of sacrificed sheep and poultry. Various ancient ...

or the

augur An augur was a priest and official in the ancient Rome, classical Roman world. His main role was the practice of augury, the interpretation of the will of the List of Roman deities, gods by studying events he observed within a predetermined s ...

s 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 "", 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 the opposing sides.

Antiquity

Aristotle Aristotle (; 384–322 BC) was an Ancient Greek philosophy, Ancient Greek philosopher and polymath. His writings cover a broad range of subjects spanning the natural sciences, philosophy, linguistics, economics, politics, psychology, a ...

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 a whole, are referred to as the ''

Organon The ''Organon'' (, meaning "instrument, tool, organ") is the standard collection of Aristotle's six works on logical analysis and dialectic. The name ''Organon'' was given by Aristotle's followers, the Peripatetics, who maintained against the ...

'' because logic is a ''tool'' for philosophical thinking. Earlier thinkers, such as those who wrote texts in the

Hippocratic corpus The Hippocratic Corpus (Latin: ''Corpus Hippocraticum''), or Hippocratic Collection, is a collection of around 60 early Ancient Greek medical works strongly associated with the physician Hippocrates and his teachings. The Hippocratic Corpus cov ...

, generally did not believe that there were organs of the body but only different ''parts'' of the body. Some alchemists (e.g.

Paracelsus Paracelsus (; ; 1493 – 24 September 1541), born Theophrastus von Hohenheim (full name Philippus Aureolus Theophrastus Bombastus von Hohenheim), was a Swiss physician, alchemist, lay theologian, and philosopher of the German Renaissance. H ...

) adopted the

Hermetic Qabalah Hermetic Qabalah () is a Western esoteric tradition involving mysticism and the occult. It is the underlying philosophy and framework for magical societies such as the Hermetic Order of the Golden Dawn, has inspired esoteric Christian organiz ...

assignment between the seven vital organs and the seven

classical planets A classical planet is an astronomical object that is visible to the naked eye and moves across the sky and its backdrop of fixed stars (the common stars which seem still in contrast to the planets), appearing as wandering stars. Visible to huma ...

as follows:

Chinese traditional medicine Traditional Chinese medicine (TCM) is an alternative medical practice drawn from traditional medicine in China. A large share of its claims are pseudoscientific, with the majority of treatments having no robust evidence of effectiveness or ...

recognizes eleven organs, associated with the five Chinese traditional elements and with

yin and yang Originating in Chinese philosophy, yin and yang (, ), also yinyang or yin-yang, is the concept of opposite cosmic principles or forces that interact, interconnect, and perpetuate each other. Yin and yang can be thought of as complementary an ...

, 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.

References

External links