RESUMO
The relationship between lenticular colloid osmotic (oncotic) pressure and intraocular pressure is discussed, with particular reference to a postulated buffering reservoir action of the lens in protecting against acute changes in intraocular pressure. A hypothesis is developed regarding acute lenticular volume changes in those species manifesting change in lens shape during accommodation. The unusually high colloid osmotic pressure of fish lenses is discussed and related to their unique means of accommodation and their susceptibility to cataract formation.
Assuntos
Pressão Intraocular/fisiologia , Cristalino/fisiologia , Acomodação Ocular , Idoso , Animais , Catarata/fisiopatologia , Peixes , Humanos , Cristalino/fisiopatologia , Modelos Biológicos , Pressão OsmóticaRESUMO
Tissue water loss that occurs in aging has important implications for health status and treatment. This article discusses known mechanisms, physiologic examples, and clinical consequences of body-water changes with age, and suggests that careful monitoring of these changes can lead to better guiding of medication and fluid administration to avoid preventable complications.
Assuntos
Envelhecimento , Água Corporal/fisiologia , Idoso , Anemia Falciforme/fisiopatologia , HumanosRESUMO
Having evolved from the sea and developed from an embryo, the species and the individual lose water--the medium and solvent wherein these processes occur--continually as they age. From an embryo, which is about 90% water, to a senescent individual in the tenth decade, there is a decline in body water to 60% or below. This loss in body water has profound effects on pathophysiology, making older persons susceptible to both under- and overhydration because they have a smaller volume of distribution for exogenous water. A colloid osmotic macromolecular aggregation model has been hypothesized to explain water loss in aging individuals.
Assuntos
Envelhecimento , Água Corporal/metabolismo , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Anemia Falciforme/metabolismo , Animais , Volume Sanguíneo , Catarata/metabolismo , Criança , Pré-Escolar , Coloides , Envelhecimento Eritrocítico , Humanos , Lactente , Recém-Nascido , Masculino , Pessoa de Meia-Idade , Pressão Osmótica , RatosRESUMO
We have evolved from the sea, are composed mostly of water, the medium and solvent wherein most vital processes occur, and phylogenetically and ontogenetically lose water continually as we age. An embryo is about 90% water, a newborn child about 80% water, a mature adult about 70% water, an older adult about 60% water with recent work indicating that in senescence the percentage of body water is actually below 60%. The mechanisms of the water loss in aging have not been elucidated. From a theoretical point of view, there is good reason to believe that there may be profound changes in the chemical potential of intracellular and interstitial water with age due to increased macromolecular interaction or aggregation from cross linking, polymerization, insolubility, etc.; all of which are known to increase with aging. The resultant increased macromolecular solute-solute interaction would be accompanied by decreased macromolecular solute-solvent interaction, thereby causing a higher solvent (water) chemical potential. This would facilitate the loss of bound water, thereby explaining the observed losses in body water with age. The ocular lens is a microcosm of aging, in that from its nucleus to cortex, the oldest to youngest cells are concentrically arranged, as in a tree. We have developed a method to directly measure lens tissue oncotic pressure in an attempt to experimentally test the above cited hypothesis.
