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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.
There are other systems in the body that are not organ systems—for example, the immune system protects the organism from infection, but it is not an organ system since it is not composed of organs. Some organs are in more than one system—for example, the nose is in the respiratory system and also serves as a sensory organ in the nervous ...
This article contains a list of organs in the human body. It is widely believed that there are 79 organs (this number goes up if you count each bone and muscle as an organ on their own, which is becoming a more common practice [1] [2]); however, there is no universal standard definition of what constitutes an organ, and some tissue groups' status as one is debated. [3]
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.
That might be an organ, a region in the body, or an anatomical structure. For example, the central nervous system and the peripheral nervous systems. Central (from Latin centralis) describes something close to the centre. [33] For example, the great vessels run centrally through the body; many smaller vessels branch from these.
Ileum, caecum and colon of rabbit, showing Appendix vermiformis on fully functional caecum The human vermiform appendix on the vestigial caecum. The appendix was once believed to be a vestige of a redundant organ that in ancestral species had digestive functions, much as it still does in extant species in which intestinal flora hydrolyze cellulose and similar indigestible plant materials. [10]
Scientists think genetically-modified animals could one day be the solution to an organ supply shortage that causes thousands of people in the U.S. to die every year waiting for a transplant.
Use of organs of mammals is not common, except for the liver, which is common to a certain degree. Examples include liver sausage (braunschweiger) and pâté. Liver and onions is a traditional, "classic" menu item in diners throughout the country, [39] often as a "blue plate special". Mammal offal is somewhat more popular in certain areas.