ABSTRACT
Living cells have developed the ability to persist in the face of a fundamental contradiction. They preserve an internal composition that is an optimal milieu for metabolic processes that are essential to the maintenance of the living state and maintain the ability to regulate that composition as a defense against external perturbations. This chapter focuses on two significant elements of cellular composition: water and small solutes such as ions, sugars, and amino acids. It provides the foundation for a quantitative understanding of osmoregulatory phenomena that makes intuitive sense and is also in accord with physical reality. The chapter highlights basic principles that apply to all osmoregulatory phenomena regardless of the organism or its environment. The basis for osmoregulation lies in the stringent control of the water and solute content of body fluid compartments. The chapter concludes with a fleeting glance at the molecular basis for the solute and water transport processes that are the basis of osmoregulation.
