Organ (biology)

From Wikipedia, the free encyclopedia
Internal organs.png
Many of the internal organs of the human body
SystemOrgan systems
Anatomical terminology

An organ is a group of tissues with similar functions. Plant life and animal life rely on many organs that co-exist in organ systems.[1] In the hierarchy of life, organs lie between tissue and organ systems. A tissue is an organizational level between cells and organs. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues. Two or more organs working together in the execution of a specific body function form an organ system, also called a biological system or body system.

A given organ's tissues can be broadly categorized as parenchyma, the tissue peculiar to (or at least archetypal of) the organ and that does the organ's specialized job, and stroma, the tissues with supportive, structural, connective, or ancillary functions. For example, in a gland, the 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 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. Functionally related organs often cooperate to form whole organ systems. Organs exist in most multicellular organisms. In single-celled organisms such as bacteria, the functional analogue of an organ is known as an organelle. In plants, there are three main organs.[2] A hollow organ is an internal organ that forms a hollow tube, or pouch such as the stomach, intestine, or bladder.

In the study of anatomy, the term viscus refers to an internal organ. Viscera is the plural form.[3][4]

The number of organs in any organism depends on which precise definition of the term one uses. By one widely used definition, 79 organs have been identified in the human body.[5]


The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils.
Strobilus of Equisetum telmateia

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.[citation needed] In conifers, 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 the shoot organ system.[6]

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 the new generation of plants (see clonal colony).


The liver and gallbladder of a sheep

Non-placozoan animals such as humans have a variety of organ systems. These specific systems are also widely studied in human anatomy. The functions of these organ systems often share significant overlap. For instance, 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.

Origin and evolution[]

Relationship of major animal lineages with indication of how long ago these animals shared a common ancestor. On the left, important organs are shown, which allows us to determine how long ago these may have evolved.

The organ level of organisation in animals can be first detected in flatworms and the more derived phyla. The less-advanced taxa (like Placozoa, Sponges and Radiata) do not show consolidation of their tissues into organs.

More complex animals are composed of different organs, which have evolved over time. For example, the liver evolved in the stem vertebrates more than 500 million years ago, while the gut and brain are even more ancient, arising in the ancestor of vertebrates, insects, and worms more than 600 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 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.[7] 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, the acquisition of new functional properties by these tissues, and novel interactions of distinct tissue types.[7]

Society and culture[]

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.[citation needed]


Human viscera

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".[8]

Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal.[9] When three or more organs are present, it is called an organ system.[10]

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 the haruspices or the augurs in order to divine the future by their shape, dimensions or other factors.[11] 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"[12] The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides.[13]


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), and to describe more abstract "parts" of an interconnected whole (e.g. his logical works, taken as a whole, are referred to as the "organon").[14]

Some alchemists (e.g. Paracelsus) adopted the Hermetic Qabalah assignment between the seven vital organs and the seven classical planets as follows: [15]

Planet Organ
Sun Heart
Moon Brain
Mercury Lungs
Venus Kidneys
Mars Gall bladder
Jupiter Liver
Saturn Spleen

Organ Procedures[]

Beginning in the 20th century[16] transplants began to occur as scientists knew more about the anatomy of organs. These came later in time as procedures were often dangerous and difficult.[17] 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 the ethical analysis. This situation continues as long as transplantation relies upon organ donors rather than technological innovation, testing, and industrial manufacturing.[citation needed]

See also[]


  1. ^ Widmaier, E P; Raff, H; Strang, KT (2014). Vander's Human Physiology (12th ed.). ISBN 978-0-07-128366-3.[page needed]
  2. ^ "Botany/Plant structure - Wikibooks, open books for an open world". Archived from the original on 2018-02-07. Retrieved 2018-02-06.
  3. ^ "Viscus - Definition". Merriam-Webster Online Dictionary. Archived from the original on 13 July 2018. Retrieved 14 December 2009.
  4. ^ "Viscera". MeSH. Archived from the original on 24 December 2013. Retrieved 14 December 2009.
  5. ^ "New organ named in digestive system". BBC News. 2017. Archived from the original on 2018-03-24. Retrieved 2018-02-05.
  6. ^ "The Plant Body | Boundless Biology". Archived from the original on 2019-01-21. Retrieved 2019-03-19.
  7. ^ Jump up to: a b Griffith, Oliver W.; Wagner, Günter P. (23 March 2017). "The placenta as a model for understanding the origin and evolution of vertebrate organs". Nature Ecology & Evolution. 1 (4): 0072. doi:10.1038/s41559-017-0072. PMID 28812655. S2CID 32213223.
  8. ^ "organ (n.)". Online Etymology Dictionary. Archived from the original on 1 May 2019. Retrieved 22 March 2019.
  9. ^ "Plant Development I: Tissue differentiation and function". Biology 1520 (Georgia Tech). Georgia Tech. Archived from the original on 3 September 2019. Retrieved 8 September 2019.
  10. ^ "Organ System - Definition and Examples | Biology Dictionary". Biology Dictionary. 2016-10-31. Archived from the original on 2018-02-10. Retrieved 2018-02-10.
  11. ^ Dickie, Matthew W. (February 23, 2003). Magic and Magicians in the Greco-Roman World (1 ed.). Routledge. p. 274. ISBN 0415311292.
  12. ^ "Parietal – Learning brain structure, function and variability from neuroimaging data". Archived from the original on 2018-02-10. Retrieved 2018-02-10.
  13. ^ "Thoracic cavity". Amboss. Amboss. Archived from the original on 21 July 2019. Retrieved 8 September 2019.
  14. ^ Lennox, James (31 Jan 2017). "Aristotle's Biology". Plato. Stanford University. Archived from the original on 7 May 2019. Retrieved 23 March 2019. Section 2: Aristotle's Philosophy of Science
  15. ^ Ball, Philip (2007). The devil's doctor. London: Arrow. ISBN 978-0-09-945787-9. OCLC 124919518. Archived from the original on 2021-08-02. Retrieved 2021-08-02.
  16. ^ "Timeline of Historical Events and Significant Milestones". Organ Donor Government Web. Archived from the original on 19 January 2019. Retrieved 19 March 2019.
  17. ^ "transplant | Definition, Types, & Rejection". Encyclopedia Britannica. Archived from the original on 2019-03-27. Retrieved 2019-03-19.

External links[]

Retrieved from ""