This book examines the physical forces - fluid shear, stretch, and gravity that play a role in the physiology of tissues and cellular functions. It gives special attention to the influences of the flow of blood and exercise on the growth of blood vessels and the flow of interstitial fluid on bone formation. Pathological conditions are also presented, such as the lack of mechanical loading on bone and osteoporosis. For biotechnologists, the problem of cell susceptibility to agitation-induced hydrodynamic forces in the scale-up of mammalian cell bioreactors is examined.