[The physiological determinants of the parallelism (unity) of histological structures].

The theory of structural parallelism put forward by A. A. Zavarzin (Senior) has been supported by the analysis of cytological specificity of effector organs involved in water-salt homeostasis, and of the excretory system of vertebrates and invertebrates. The similarity in morphofunctional organization of different excretory organs (i.e. the presence of ultrafiltration apparatus and cells which make it possible to absorb all vitally important substances) is likely to result from the fact that the excretory organ should excrete not only the final products of metabolism, but also any exogenic substances in addition to those which although important, are excessive for the organism. The brush border of asymmetrical epithelial cells of excretory organs is presumably a morphological expression of the structure which accounts for the inward transport of all physiologically important substances. Specificity of the membrane mechanism of water and sodium transport accounts for the identical principles in the structure of cells and areas of cell contacts of epithelia in different organs involved in the formation of hypotonic (saliva glands, renal tubules) or hypertonic fluids (salt glands, marine teleost gills).