- published: 29 Nov 2012
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In biology, an organ or viscus is a collection of tissues joined in a structural unit to serve a common function. In anatomy, a viscus /ˈvɪskəs/ is an internal organ, and viscera is the plural form.
Organs are composed of main tissue, parenchyma, and "sporadic" tissues, stroma. The main tissue is that which is unique for the specific organ, such as the myocardium, the main tissue of the heart, while sporadic tissues include the nerves, blood vessels, and connective tissues. Functionally related organs often cooperate to form whole organ systems. Organs exist in all higher biological organisms, in particular they are not restricted to animals, but can also be identified in plants. In single-cell organisms like bacteria, the functional analogue of an organ is called organelle.
A hollow organ is a visceral organ that forms a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity, like the heart or urinary bladder.
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. The functions of 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.
Organ may refer to the following:
Anatomy is the branch of biology concerned with the study of the structure of organisms and their parts. In some of its facets, anatomy is related to embryology and comparative anatomy, which itself is closely related to evolutionary biology and phylogeny.Human anatomy is one of the basic essential sciences of medicine.
The discipline of anatomy is divided into macroscopic and microscopic anatomy. Macroscopic anatomy, or gross anatomy, is the examination of an animal's body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, and also in the study of cells.
The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th century medical imaging techniques including X-ray, ultrasound, and magnetic resonance imaging.