What are organs? Organs are collections of tissues that are joined in a structural unit with purpose of serving a common function. They are consisted of a main tissue which is called parenchzma and sporadic tissues, that are called stroma. For a specific organ, the main tissue is the one that is unique fo the specific organ, while spradic tissues include nerves, blood 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 they can also be identified in plans. Single-cell organisms, like bacteria, the functional analogues of organs arecalled organelles. A hollow organ is a visceral organ that is a hollow tube or pouch, such as the stomach or intestine, or that includes a cavity, like the heart or urinary bladder.
The origin of the English word “organ” is deriveted from the Latin organum, which means instrument, which is drawn from the Greek word organon, that means implement, musical instrument or organ of the body. The philosopher Aristotle used the word very often in his philosophy, both to descripe the organs of plants and animals and to describe more abstract pars of an interconnected whole.
More on the specific human organs will be presented to you in later texts.