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Author(s): Wade Haaland

The Internal Milieu

The cell is the simplest unit of life. Unicellular organisms typically perform all of life's functions. The cells of a multicellular organism, however, depend on other cells for their health, and also are responsible for the health and proper functioning of other cells and the organism as a whole.  

To survive, the cell needs a relatively stable internal milieu. Cells within an organism make up body systems. In turn, body systems respond to some external changes in ways that lessen the impact of those changes on the body, and thus, help to maintain the stable internal environment ("internal milieu") needed by cells.