Organ and Organ System

In a multicellular animal the basic types of tissues do not work in isolation. They organise, in specific proportion and pattern, to build the next level of structure. A group of tissues arranged and integrated to carry out one or more particular functions constitutes an organ — the stomach, lung, heart and kidney are familiar examples. Each organ in the body is made of one or more of the four basic tissue types; the heart, for instance, contains all four — epithelial, connective, muscular and neural tissue.

Organs rarely act alone either. When two or more organs cooperate, through their physical and/or chemical interactions, to accomplish a common function, they together form an organ system, such as the digestive system or the respiratory system. This layered arrangement — cells to tissues to organs to organ systems — is essential for the more efficient and better-coordinated activity of the millions of cells that make up an organism. …