RESEARCH STARTER

Organ (anatomy)

In anatomy, an organ is a structured collection of cells and tissues that work together to perform specific functions within a living organism. Both plants and animals have organs, with the study of plant organs termed plant morphology and the study of animal organs referred to as anatomy. Organs can vary widely; some, like the liver, consist of solid tissue, while others, such as the heart and stomach, contain cavities for transporting materials like blood and food. Each organ typically collaborates with others in organ systems, which are groups of organs that perform related functions, such as the digestive system.

The concept of organs has deep historical and cultural significance, with various societies attributing different meanings and associations to specific organs. For example, the heart is often linked to emotions like love, while the brain is considered the center of consciousness. Advancements in medical technology have transformed the field of organ study, enabling noninvasive techniques to observe organ function in live patients. Furthermore, organ transplantation has emerged as a critical medical procedure, though challenges such as organ rejection remain prevalent. The classification and number of organs in the human body have been subjects of ongoing debate, leading to the recent reclassification of structures like the mesentery as distinct organs. This complexity illustrates the evolving understanding of anatomy and its vital role in health and medicine.

Full Article

In anatomy, an organ is a quantity of tissue that has formed into an organized collection of cells in order to cooperatively perform an overall function. Both plants and animals can have organs; the study of plant form and structure, including organs, is referred to as plant morphology, while the study of animal organs is known as anatomy. A single organ is also known as a viscus (plural viscera).

Some organs, such as the liver, are solid masses of tissue. Other organs, such as the heart and the stomach, have one or more cavities inside. These cavities are typically used to transport material throughout the organism, as when the heart’s chambers circulate blood or the stomach receives food and transfers it to the intestines.

Background

The word “organ” is derived from Latin and Ancient Greek, where it originally meant “instrument” in the sense of a thing that performs a function, not unlike a tool or even a musical instrument. While organs exist as independent entities within the organism, they often are part of larger organ systems that are composed of several interrelated yet distinct organs, each performing separate but complementary functions. For example, the digestive system is an organ system that includes the stomach, the small intestine, the large intestine, the liver, and the pancreas, among other organs. Each organ works with the other members of the system to accomplish the overall goal of acquiring nutrients for the body’s sustenance.

Overview

Anatomy, or the study of the body’s parts and their functions, has a long and colorful history. Anatomy can be thought of on two different scales: gross (or macroscopic) anatomy, which refers to the study of organs and organ systems with the unaided eye, and microscopic anatomy, which is the study of organs using microscopes and other means of ocular amplification.

In ancient Egypt, it was thought that organs either performed certain functions or pertained to specific deities, and Egyptians believed that organs needed to be preserved for use in the afterlife, just like the bodies they mummified. When an individual died, the body’s organs were stored in canopic jars within the burial chamber. Each organ was kept in a jar carved in the likeness of the god to whom it pertained. For example, the stomach was kept in a jar that resembled the god Duamutef, distinctive for his jackal-like head.

Throughout history, different cultures have developed associations between organs and specific personality traits. The most common example is the modern association of the heart with love, passion, and intense emotion. The association between love and the human heart is seen in such traditions as wearing a wedding ring on the ring finger of the left hand; it was once believed that the vena amoris (literally, “vein of love” in Latin) ran directly from the heart to this finger. All fingers on both hands, however, share the same type of vein structure. Similarly, the brain is often viewed as the seat of consciousness, and there is frequent philosophical disagreement about whether the soul resides in the brain, the heart, or somewhere else entirely. The eyes are sometimes considered the “windows to the soul,” and the digestive organs have even been linked to subconscious intuition, such as having a “gut feeling” about someone or something.

Many cultures, including the Greeks, Romans, Etruscans, Babylonians, Assyrians, and Hittites, practiced a form of augury, or fortune-telling, known as haruspicy. In this ritual, a haruspex would sacrifice an animal and then look at the condition, position, and other characteristics of its internal organs (usually the intestines) in order to foretell what would or would not happen in the future.

Long ago, the only way for scientists and physicians to study organs was to have access to a corpse, which was challenging due to religious and cultural taboos pertaining to death and decay. In the twentieth century, the growing use of technologies such as X-rays, magnetic resonance imaging (MRI), ultrasounds, and positron emission tomography (PET) scanning allowed physicians and scientists to noninvasively observe and study functioning organs in a live patient. It is even possible to observe what parts of the brain become more neurochemically active in response to stimuli such as flashing lights, which helps scientists understand what sections of the brain are responsible for particular types of information processing (long-term memory, short-term memory, sensory stimulation, emotion regulation, and so forth).

Science has also advanced to make organ transplantation possible. A functioning and healthy organ is removed from one body and is surgically inserted (transplanted) into the body of another patient, whose original organ has either been damaged or suffered from a defect that prevented it from operating appropriately. It is possible to transplant entire organs as well as tissue such as skin or bone marrow. In a few cases, it is possible for a living person to donate tissue or an organ—a healthy person has two kidneys, for example, but can live with only one—but most organ donors are recently deceased.

A frequent problem with organ transplant procedures is organ rejection, in which the recipient’s body rejects the donated organ as an intrusion and treats it as an invasive disease, causing the immune system to attack the newly received organ or tissue and the transplant to fail. Doctors continued to study how organs operate so they could work to suppress this immune response and thereby increase the likelihood of success in organ-transplant procedures. Amid an ongoing shortage of viable organs for transplantation, scientists specifically experimented further with the potential to transplant organs from genetically modified nonhuman sources (particularly pigs) into humans. In 2024, marking a milestone in the field, a surgical team at Massachusetts General Hospital transplanted a genetically modified pig kidney into a living human recipient successfully. The following year, the fourth US recipient of such a kidney set a record when the organ was removed after he had lived with it for almost nine months.

Organ Number

For centuries, scientists, researchers, anatomists, physicians, and lay people have been unable to agree on a definitive and specific list of organs in the human body, with many people defining an organ as anything solid that has a specific function in the body, such as bones, and others narrowing that interpretation to define an organ as something solid that provides a vital, life-sustaining function in the body. Others are adamant that an organ must be inside the body, which discounts listing the skin as an organ. Many anatomists feel that a standard definition of what constitutes an organ is crucial in an age of artificial intelligence and computerized search engines that deal in hierarchical relationships of named and categorized things. Despite this confusion and disagreement over organ number and definition, an organ was validated in a November 2016 report published in The Lancet Gastroenterology & Hepatology—the mesentery. Until the late 1800s, the mesentery had been classified as an organ, but in 1885, Sir Frederick Treves presented findings, which also contributed to later interpretations, that the mesentery was not one continuous structure, as had been previously believed, but was instead fragmented tissue and part of the small intestine and colon. With the use of radiological imaging and surgical access, J. Calvin Coffey of the University of Limerick was able to prove that the mesentery is a continuous organ by establishing its anatomy and structure.


Bibliography

Chase, Brandon. “World’s First Genetically-Edited Pig Kidney Transplant into Living Recipient Performed at Massachusetts General Hospital.” Massachusetts General Hospital, 21 Mar. 2024, www.massgeneral.org/news/press-release/worlds-first-genetically-edited-pig-kidney-transplant-into-living-recipient. Accessed 4 Mar. 2026.

Christensen, Jen. “Doctors Say They’re ‘Measurably Closer’ to Making Pig Kidneys Work for Humans.” CNN, 13 Nov. 2025, www.cnn.com/2025/11/13/health/pig-kidney-transplant-studies. Accessed 10 Mar. 2026.

Coffey, J. Calvin, and D. Peter O’Leary. “The Mesentery: Structure, Function, and Role in Disease.” The Lancet: Gastroenterology & Hepatology, vol. 1, no. 3, Nov. 2016, pp. 238–47, doi:10.1016/S2468-1253(16)30026-7. Accessed 4 Mar. 2026.

Ferber, Sarah, and Sally Wilde, editors. The Body Divided: Human Beings and Human “Material” in Modern Medical History. Ashgate, 2011.

Hamilton, David. A History of Organ Transplantation: Ancient Legends to Modern Practice. U of Pittsburgh P, 2012.

Healey, Justin, editor. Organ and Tissue Donation. Spinney, 2011.

Kliegel, Ewald. Let Your Body Speak: The Essential Nature of Our Organs. Illustrated by Anne Heng, translated by Sabine Weeke, Findhorn, 2013.

Le, Tao, et al. First Aid for the Basic Sciences: Organ Systems. 2nd ed., McGraw, 2012.

“Mesentery.” Cleveland Clinic, 4 Sept. 2025, my.clevelandclinic.org/health/body/mesentery. Accessed 10 Mar. 2026.

Saladin, Kenneth. Anatomy & Physiology: The Unity of Form and Function. 10th ed., McGraw Hill, 2023.

Trzepacz, Paula T., and Andrea F. DiMartini. The Transplant Patient: Biological, Psychiatric and Ethical Issues in Organ Transplantation. Cambridge UP, 2000.

Widmaier, Eric P., Hershel Raff, and Kevin T. Strang. Vander’s Human Physiology: The Mechanisms of Body Function. 13th ed., McGraw, 2014.

Full Article

In anatomy, an organ is a quantity of tissue that has formed into an organized collection of cells in order to cooperatively perform an overall function. Both plants and animals can have organs; the study of plant form and structure, including organs, is referred to as plant morphology, while the study of animal organs is known as anatomy. A single organ is also known as a viscus (plural viscera).

Some organs, such as the liver, are solid masses of tissue. Other organs, such as the heart and the stomach, have one or more cavities inside. These cavities are typically used to transport material throughout the organism, as when the heart’s chambers circulate blood or the stomach receives food and transfers it to the intestines.

Background

The word “organ” is derived from Latin and Ancient Greek, where it originally meant “instrument” in the sense of a thing that performs a function, not unlike a tool or even a musical instrument. While organs exist as independent entities within the organism, they often are part of larger organ systems that are composed of several interrelated yet distinct organs, each performing separate but complementary functions. For example, the digestive system is an organ system that includes the stomach, the small intestine, the large intestine, the liver, and the pancreas, among other organs. Each organ works with the other members of the system to accomplish the overall goal of acquiring nutrients for the body’s sustenance.

Overview

Anatomy, or the study of the body’s parts and their functions, has a long and colorful history. Anatomy can be thought of on two different scales: gross (or macroscopic) anatomy, which refers to the study of organs and organ systems with the unaided eye, and microscopic anatomy, which is the study of organs using microscopes and other means of ocular amplification.

In ancient Egypt, it was thought that organs either performed certain functions or pertained to specific deities, and Egyptians believed that organs needed to be preserved for use in the afterlife, just like the bodies they mummified. When an individual died, the body’s organs were stored in canopic jars within the burial chamber. Each organ was kept in a jar carved in the likeness of the god to whom it pertained. For example, the stomach was kept in a jar that resembled the god Duamutef, distinctive for his jackal-like head.

Throughout history, different cultures have developed associations between organs and specific personality traits. The most common example is the modern association of the heart with love, passion, and intense emotion. The association between love and the human heart is seen in such traditions as wearing a wedding ring on the ring finger of the left hand; it was once believed that the vena amoris (literally, “vein of love” in Latin) ran directly from the heart to this finger. All fingers on both hands, however, share the same type of vein structure. Similarly, the brain is often viewed as the seat of consciousness, and there is frequent philosophical disagreement about whether the soul resides in the brain, the heart, or somewhere else entirely. The eyes are sometimes considered the “windows to the soul,” and the digestive organs have even been linked to subconscious intuition, such as having a “gut feeling” about someone or something.

Many cultures, including the Greeks, Romans, Etruscans, Babylonians, Assyrians, and Hittites, practiced a form of augury, or fortune-telling, known as haruspicy. In this ritual, a haruspex would sacrifice an animal and then look at the condition, position, and other characteristics of its internal organs (usually the intestines) in order to foretell what would or would not happen in the future.

Long ago, the only way for scientists and physicians to study organs was to have access to a corpse, which was challenging due to religious and cultural taboos pertaining to death and decay. In the twentieth century, the growing use of technologies such as X-rays, magnetic resonance imaging (MRI), ultrasounds, and positron emission tomography (PET) scanning allowed physicians and scientists to noninvasively observe and study functioning organs in a live patient. It is even possible to observe what parts of the brain become more neurochemically active in response to stimuli such as flashing lights, which helps scientists understand what sections of the brain are responsible for particular types of information processing (long-term memory, short-term memory, sensory stimulation, emotion regulation, and so forth).

Science has also advanced to make organ transplantation possible. A functioning and healthy organ is removed from one body and is surgically inserted (transplanted) into the body of another patient, whose original organ has either been damaged or suffered from a defect that prevented it from operating appropriately. It is possible to transplant entire organs as well as tissue such as skin or bone marrow. In a few cases, it is possible for a living person to donate tissue or an organ—a healthy person has two kidneys, for example, but can live with only one—but most organ donors are recently deceased.

A frequent problem with organ transplant procedures is organ rejection, in which the recipient’s body rejects the donated organ as an intrusion and treats it as an invasive disease, causing the immune system to attack the newly received organ or tissue and the transplant to fail. Doctors continued to study how organs operate so they could work to suppress this immune response and thereby increase the likelihood of success in organ-transplant procedures. Amid an ongoing shortage of viable organs for transplantation, scientists specifically experimented further with the potential to transplant organs from genetically modified nonhuman sources (particularly pigs) into humans. In 2024, marking a milestone in the field, a surgical team at Massachusetts General Hospital transplanted a genetically modified pig kidney into a living human recipient successfully. The following year, the fourth US recipient of such a kidney set a record when the organ was removed after he had lived with it for almost nine months.

Organ Number

For centuries, scientists, researchers, anatomists, physicians, and lay people have been unable to agree on a definitive and specific list of organs in the human body, with many people defining an organ as anything solid that has a specific function in the body, such as bones, and others narrowing that interpretation to define an organ as something solid that provides a vital, life-sustaining function in the body. Others are adamant that an organ must be inside the body, which discounts listing the skin as an organ. Many anatomists feel that a standard definition of what constitutes an organ is crucial in an age of artificial intelligence and computerized search engines that deal in hierarchical relationships of named and categorized things. Despite this confusion and disagreement over organ number and definition, an organ was validated in a November 2016 report published in The Lancet Gastroenterology & Hepatology—the mesentery. Until the late 1800s, the mesentery had been classified as an organ, but in 1885, Sir Frederick Treves presented findings, which also contributed to later interpretations, that the mesentery was not one continuous structure, as had been previously believed, but was instead fragmented tissue and part of the small intestine and colon. With the use of radiological imaging and surgical access, J. Calvin Coffey of the University of Limerick was able to prove that the mesentery is a continuous organ by establishing its anatomy and structure.


Bibliography

Chase, Brandon. “World’s First Genetically-Edited Pig Kidney Transplant into Living Recipient Performed at Massachusetts General Hospital.” Massachusetts General Hospital, 21 Mar. 2024, www.massgeneral.org/news/press-release/worlds-first-genetically-edited-pig-kidney-transplant-into-living-recipient. Accessed 4 Mar. 2026.

Christensen, Jen. “Doctors Say They’re ‘Measurably Closer’ to Making Pig Kidneys Work for Humans.” CNN, 13 Nov. 2025, www.cnn.com/2025/11/13/health/pig-kidney-transplant-studies. Accessed 10 Mar. 2026.

Coffey, J. Calvin, and D. Peter O’Leary. “The Mesentery: Structure, Function, and Role in Disease.” The Lancet: Gastroenterology & Hepatology, vol. 1, no. 3, Nov. 2016, pp. 238–47, doi:10.1016/S2468-1253(16)30026-7. Accessed 4 Mar. 2026.

Ferber, Sarah, and Sally Wilde, editors. The Body Divided: Human Beings and Human “Material” in Modern Medical History. Ashgate, 2011.

Hamilton, David. A History of Organ Transplantation: Ancient Legends to Modern Practice. U of Pittsburgh P, 2012.

Healey, Justin, editor. Organ and Tissue Donation. Spinney, 2011.

Kliegel, Ewald. Let Your Body Speak: The Essential Nature of Our Organs. Illustrated by Anne Heng, translated by Sabine Weeke, Findhorn, 2013.

Le, Tao, et al. First Aid for the Basic Sciences: Organ Systems. 2nd ed., McGraw, 2012.

“Mesentery.” Cleveland Clinic, 4 Sept. 2025, my.clevelandclinic.org/health/body/mesentery. Accessed 10 Mar. 2026.

Saladin, Kenneth. Anatomy & Physiology: The Unity of Form and Function. 10th ed., McGraw Hill, 2023.

Trzepacz, Paula T., and Andrea F. DiMartini. The Transplant Patient: Biological, Psychiatric and Ethical Issues in Organ Transplantation. Cambridge UP, 2000.

Widmaier, Eric P., Hershel Raff, and Kevin T. Strang. Vander’s Human Physiology: The Mechanisms of Body Function. 13th ed., McGraw, 2014.

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