If you put erythrocytes in a hypertonic solution, such is the blood with abnormally high sodium, the concentration of the solutes will be greater outside the erythrocytes. This means that the water concentration of the erythrocites is higher than that of the blood. Since the aim is to balance water concentration on the inside and outside of the cell, the water will exit the erythrocytes. They will lose water and, consequently, will shrink in size.
