Organ (biology)

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Organ
Internal organs.png
Many of the internal organs of the human body
Details
System Organ systems
Identifiers
Greek Οργανο
FMA 67498
Anatomical terminology

In a multicellular organism, an organ is a collection of tissues joined in a structural unit to serve a common function. [1] In the hierarchy of life, an organ lies between tissue and an organ system. Tissues are formed from same type cells 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 and smooth muscle tissue. [2] 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.

Contents

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 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. [3]

The number of organs in any organism depends on the definition used. By one widely adopted definition, 79 organs have been identified in the human body. [4]

Animals

The liver and gallbladder of a sheep Leber Schaf.jpg
The liver and gallbladder of a sheep

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, 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.

Viscera

In the study of anatomy, viscera (SG: viscus) refers to the internal organs of the abdominal, thoracic, and pelvic cavities. [5] The abdominal organs may be classified as solid organs or hollow organs. The solid organs are the liver, pancreas, spleen, kidneys, and adrenal glands. The hollow organs of the abdomen are the stomach, intestines, gallbladder, bladder, and rectum. [6] In the thoracic cavity, the heart is a hollow, muscular organ. [7] Splanchnology is the study of the viscera. [8] The term "visceral" is contrasted with the term "parietal", meaning "of or relating to the wall of a body part, organ or cavity". [9] The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides. [10]

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. Origin of major organs on the animal phylogeny.jpg
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, 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, 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 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. [11] 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. [11]

Plants

The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils. Red Hibiscus in Chennai during Spring.JPG
The flower is the angiosperm's reproductive organ. This Hibiscus flower is hermaphroditic, and it contains stamen and pistils.
Strobilus of Equisetum telmateia Equisetum telmateia strob.jpg
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. [12]

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).

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 ]

Organ transplants

Beginning in the 20th century [13] 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. [14] 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 ]

History

Human viscera View of Viscera Page 82.jpg
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". [15]

Plant organs are made from tissue composed of different types of tissue. The three tissue types are ground, vascular, and dermal. [16] When three or more organs are present, it is called an organ system. [17]

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. [18] 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" [9] The two terms are often used in describing a membrane or piece of connective tissue, referring to the opposing sides. [19]

Antiquity

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 ). [20]

Some alchemists (e.g. Paracelsus) adopted the Hermetic Qabalah assignment between the seven vital organs and the seven classical planets as follows: [21]

PlanetOrgan
SunHeart
MoonBrain
MercuryLungs
VenusKidneys
MarsGall bladder
JupiterLiver
SaturnSpleen

Chinese traditional medicine recognizes eleven organs, associated with the five Chinese traditional elements and with yin and yang, as follows:

ElementYin/yangOrgan
Woodyinliver
yanggall bladder
Fireyinheart
yangsmall intestine / san jiao
Earthyinspleen
yangstomach
Metalyinlungs
yanglarge intestine
Wateryinkidneys
yangbladder

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.

See also

Related Research Articles

<span class="mw-page-title-main">Anatomy</span> Study of the structure of organisms and their parts

Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and physiology, which study the structure and function of organisms and their parts respectively, make a natural pair of related disciplines, and are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine.

<span class="mw-page-title-main">Ovary</span> Female reproductive organ that produces egg cells

The ovary is a gonad in the female reproductive system that produces ova. When an ovum is released, this travels down the fallopian tube into the uterus. There is an ovary found on the left and the right side of the body. The ovaries also secrete hormones that play a role in the menstrual cycle and fertility. The ovary progresses through many stages beginning in the prenatal period through menopause. It is also an endocrine gland because of the various hormones that it secretes.

<span class="mw-page-title-main">Skeleton</span> Part of the body that forms the supporting structure

A skeleton is the structural frame that supports the body of most animals. There are several types of skeletons, including the exoskeleton, which is a rigid outer shell that holds up an organism's shape; the endoskeleton, a rigid internal frame to which the organs and soft tissues attach; and the hydroskeleton, a flexible internal structure supported by the hydrostatic pressure of body fluids.

<span class="mw-page-title-main">Embryo</span> Multicellular diploid eukaryote in its earliest stage of development

An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm cell. The resulting fusion of these two cells produces a single-celled zygote that undergoes many cell divisions that produce cells known as blastomeres. The blastomeres are arranged as a solid ball that when reaching a certain size, called a morula, takes in fluid to create a cavity called a blastocoel. The structure is then termed a blastula, or a blastocyst in mammals.

<span class="mw-page-title-main">Lung</span> Primary organ of the respiratory system

The lungs are the most important organs of the respiratory system in humans and most other animals, including some snails and a small number of fish. In mammals and most other vertebrates, two lungs are located near the backbone on either side of the heart. Their function in the respiratory system is to extract oxygen from the air and transfer it into the bloodstream, and to release carbon dioxide from the bloodstream into the atmosphere, in a process of gas exchange. The pleurae, which are thin, smooth, and moist, serve to reduce friction between the lungs and chest wall during breathing, allowing for easy and effortless movements of the lungs.

<span class="mw-page-title-main">Human body</span> Entire structure of a human being

The human body is the entire structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organs and then organ systems. They ensure homeostasis and the viability of the human body.

<span class="mw-page-title-main">Integumentary system</span> Skin and other protective organs

The integumentary system is the set of organs forming the outermost layer of an animal's body. It comprises the skin and its appendages, which act as a physical barrier between the external environment and the internal environment that it serves to protect and maintain the body of the animal. Mainly it is the body's outer skin.

<span class="mw-page-title-main">Abdominal cavity</span> Body cavity in the abdominal area

The abdominal cavity is a large body cavity in humans and many other animals that contain organs. It is a part of the abdominopelvic cavity. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm, a thin sheet of muscle under the lungs, and its floor is the pelvic inlet, opening into the pelvis.

<span class="mw-page-title-main">Tissue (biology)</span> Group of cells having similar appearance and performing the same function

In biology, tissue is a historically derived biological organizational level between cells and a complete organ. A tissue is therefore often thought of as an assembly of similar cells and their extracellular matrix from the same embryonic origin that together carry out a specific function. Organs are then formed by the functional grouping together of multiple tissues.

<span class="mw-page-title-main">Loose connective tissue</span> Type of connective tissue in animals

Loose connective tissue, also known as areolar tissue, is a cellular connective tissue with thin and relatively sparse collagen fibers. They have a semi-fluid matrix with lesser proportions of fibers. Its ground substance occupies more volume than the fibers do. It has a viscous to gel-like consistency and plays an important role in the diffusion of oxygen and nutrients from the capillaries that course through this connective tissue as well as in the diffusion of carbon dioxide and metabolic wastes back to the vessels. Moreover, loose connective tissue is primarily located beneath the epithelia that cover the body surfaces and line the internal surfaces of the body. It is also associated with the epithelium of glands and surrounds the smallest blood vessels. This tissue is thus the initial site where pathogenic agents, such as bacteria that have breached an epithelial surface, are challenged and destroyed by cells of the immune system.

The nephridium is an invertebrate organ, found in pairs and performing a function similar to the vertebrate kidneys. Nephridia remove metabolic wastes from an animal's body. Nephridia come in two basic categories: metanephridia and protonephridia. All nephridia- and kidney- having animals belong to the clade Nephrozoa.

A biological system is a complex network which connects several biologically relevant entities. Biological organization spans several scales and are determined based different structures depending on what the system is. Examples of biological systems at the macro scale are populations of organisms. On the organ and tissue scale in mammals and other animals, examples include the circulatory system, the respiratory system, and the nervous system. On the micro to the nanoscopic scale, examples of biological systems are cells, organelles, macromolecular complexes and regulatory pathways. A biological system is not to be confused with a living system, such as a living organism.

<span class="mw-page-title-main">Stroma (tissue)</span> Part of a tissue or organ with a structural or connective role

Stroma is the part of a tissue or organ with a structural or connective role. It is made up of all the parts without specific functions of the organ - for example, connective tissue, blood vessels, ducts, etc. The other part, the parenchyma, consists of the cells that perform the function of the tissue or organ.

Insect physiology includes the physiology and biochemistry of insect organ systems.

<span class="mw-page-title-main">Scrotum</span> Sac of skin that protects the testicles

In most terrestrial mammals, the scrotum or scrotal sac is a part of the external male genitalia located at the base of the penis that consists of a suspended dual-chambered sac of skin and smooth muscle. The scrotum contains the external spermatic fascia, testicles, epididymis, and ductus deferens. It is a distention of the perineum and carries some abdominal tissues into its cavity including the testicular artery, testicular vein, and pampiniform plexus. The perineal raphe is a small, vertical, slightly raised ridge of scrotal skin under which is found the scrotal septum. It appears as a thin longitudinal line that runs front to back over the entire scrotum. In humans, the scrotum becomes covered with pubic hair at puberty. The scrotum will usually tighten during penile erection and when exposed to cold temperatures. One testis is typically lower than the other to avoid compression in the event of an impact.

The reproductive system of an organism, also known as the genital system, is the biological system made up of all the anatomical organs involved in sexual reproduction. Many non-living substances such as fluids, hormones, and pheromones are also important accessories to the reproductive system. Unlike most organ systems, the sexes of differentiated species often have significant differences. These differences allow for a combination of genetic material between two individuals, which allows for the possibility of greater genetic fitness of the offspring.

<span class="mw-page-title-main">Allorecognition</span>

Allorecognition is the ability of an individual organism to distinguish its own tissues from those of another. It manifests itself in the recognition of antigens expressed on the surface of cells of non-self origin. Allorecognition has been described in nearly all multicellular phyla.

This glossary of biology terms is a list of definitions of fundamental terms and concepts used in biology, the study of life and of living organisms. It is intended as introductory material for novices; for more specific and technical definitions from sub-disciplines and related fields, see Glossary of cell biology, Glossary of genetics, Glossary of evolutionary biology, Glossary of ecology, Glossary of environmental science and Glossary of scientific naming, or any of the organism-specific glossaries in Category:Glossaries of biology.

The development of the digestive system in the human embryo concerns the epithelium of the digestive system and the parenchyma of its derivatives, which originate from the endoderm. Connective tissue, muscular components, and peritoneal components originate in the mesoderm. Different regions of the gut tube such as the esophagus, stomach, duodenum, etc. are specified by a retinoic acid gradient that causes transcription factors unique to each region to be expressed. Differentiation of the gut and its derivatives depends upon reciprocal interactions between the gut endoderm and its surrounding mesoderm. Hox genes in the mesoderm are induced by a Hedgehog signaling pathway secreted by gut endoderm and regulate the craniocaudal organization of the gut and its derivatives. The gut system extends from the oropharyngeal membrane to the cloacal membrane and is divided into the foregut, midgut, and hindgut.

A tissue membrane is a thin layer or sheet of cells that covers the outside of the body, the organs, internal passageways that lead to the exterior of the body, and the lining of the moveable joint cavities. There are two basic types of tissue membranes: connective tissue and epithelial membranes.

References

  1. ↑ Widmaier, E P; Raff, H; Strang, KT (2014). Vander's Human Physiology (12th ed.). McGraw-Hill Higher Education. ISBN   978-0-07-128366-3.[ page needed ]
  2. ↑ Kent, Michael (2000). Advanced biology. Oxford: Oxford University Press. p. 81. ISBN   0199141959.
  3. ↑ "Botany/Plant structure – Wikibooks, open books for an open world". en.wikibooks.org. Archived from the original on 2018-02-07. Retrieved 2018-02-06.
  4. ↑ "New organ named in digestive system". BBC News. 2017. Archived from the original on 2018-03-24. Retrieved 2018-02-05.
  5. ↑ Bell, Daniel J. "Viscera | Radiology Reference Article | Radiopaedia.org". Radiopaedia.
  6. ↑ Bell, Daniel J. "Solid and hollow abdominal viscera | Radiology Reference Article | Radiopaedia.org". Radiopaedia. Retrieved 24 November 2021.
  7. ↑ "Biology of the Heart – Heart and Blood Vessel Disorders". MSD Manual Consumer Version. Retrieved 24 November 2021.
  8. ↑ "Medical Definition of SPLANCHNOLOGY". www.merriam-webster.com. Retrieved 25 November 2021.
  9. 1 2 "Parietal – Learning brain structure, function and variability from neuroimaging data". team.inria.fr. Archived from the original on 2018-02-10. Retrieved 2018-02-10.
  10. ↑ "Thoracic cavity". Amboss. Archived from the original on 21 July 2019. Retrieved 8 September 2019.
  11. 1 2 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. Bibcode:2017NatEE...1...72G. doi:10.1038/s41559-017-0072. PMID   28812655. S2CID   32213223.
  12. ↑ "The Plant Body | Boundless Biology". courses.lumenlearning.com. Archived from the original on 2019-01-21. Retrieved 2019-03-19.
  13. ↑ "Timeline of Historical Events and Significant Milestones". Organ Donor Government Web. Archived from the original on 19 January 2019. Retrieved 19 March 2019.
  14. ↑ "transplant | Definition, Types, & Rejection". Encyclopedia Britannica. Archived from the original on 2019-03-27. Retrieved 2019-03-19.
  15. ↑ "organ (n.)". Online Etymology Dictionary . Archived from the original on 1 May 2019. Retrieved 22 March 2019.
  16. ↑ "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.
  17. ↑ "Organ System – Definition and Examples | Biology Dictionary". Biology Dictionary. 2016-10-31. Archived from the original on 2018-02-10. Retrieved 2018-02-10.
  18. ↑ Dickie, Matthew W. (February 23, 2003). Magic and Magicians in the Greco-Roman World (1 ed.). Routledge. p. 274. ISBN   0415311292.
  19. ↑ "Thoracic cavity". Amboss. Archived from the original on 21 July 2019. Retrieved 8 September 2019.
  20. ↑ 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
  21. ↑ 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.
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