Barrier dynamics in physiological aging

Approximately 40 years ago the author initiated work which led to the 'Diffusion Theory of Aging'. Due to the net differential rate of deposition of interstitial constituents the transfer of molecules through this milieu becomes modified with advancing age so that delivery of nutrients to the interior of the cells becomes inappropriate to maintain the physiology of youthful cells. Later it was proposed that superhomeostatic events could leave irreversible residues which would further contribute to this 'malnutrition'. The role of pericellular proteins and the plasma membrane was then unknown. Now they are much better understood as final barriers to the entrance and departure of molecules into and from the cell interior and they can be modified by age. Thus is proposed the 'Barrier Dynamics Hypothesis of Aging'.