Topic overview

Start with the big picture

Structural organization begins with atoms and molecules, which provide the materials and interactions underlying cellular function. Cells are the smallest living units; groups of similar cells and extracellular matrix form tissues, and two or more tissue types combine into organs with specialized tasks. Coordinating organs form organ systems, whose integrated activity sustains the organism. As organization becomes more complex, emergent properties arise that cannot be predicted from lower levels alone. The hierarchy also involves interdependence: a change such as a gene mutation can affect proteins, cells, and organs. Homeostatic control operates across levels, while fluid compartments and therapeutic approaches can be considered in relation to this organization.