Organ (anatomy)

In biology and anatomy, an organ (Latin: organum, "instrument, tool", from Greek ὄργανον - organon, "organ, instrument, tool) is a collection of tissues joined in structural unit to serve a common function.click here

Usually there is a main tissue and sporadic tissues. The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are the nerves, blood, connective etc.. 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 analogues of organs are called organelles.A hollow organ is a visceral organ that is a hollow tube or pouch (as the stomach or intestine) or that includes a cavity (as of the heart or urinary bladder).