Difference in Geometry of Young and Old Human Erythrocytes Explained by a Filtering Mechanism

Abstract

A mechanism for the geometric difference between young and old human red blood cells is proposed. It is assumed that the bone marrow produces a population of cells with a range of sizes and shapes, but only those cells which can pass through a theoretical 3.65µ, cylindrical channel survive in the circulation. The important geometric parameters of an erythrocyte are the area and the volume. We suggest that as cells age they have a constant area but swell in proportion to their original volume. This hypothesis of aging was tested on 1,016 normal cells using the IBM 7040 computer. When the cells were theoretically swelled by approximately 15%, the population of cells which could still pass through the filter had a smaller mean area and volume and were more osmotically fragile than the same cells before swelling. Young and old cells were separated by centrifugation. The heaviest 10% of the cells (old cells) had a lower diameter, area, and volume and higher sphericity index than the lightest 20% (young cells). The calculated minimum filter diameter was not significantly different. The good agreement between the predicted and observed changes in cellular geometry between young and old cells provides supporting evidence that a cylindrical filter exists in the circulation and may play a role in determining the life span of the erythrocyte.