Electronmicroscopicic Studies on Renal Tubules

I. On the Tubular Findings of Normal and Glomerulonephritic Human Cases Gengo Osawa

Abstract

Of human kidney with clinically nomal findings and with glomerulonephritic changes, the fine structure of tubular epithelial cells were examined through electronmicroscopy using ultrathin sections of biopsy specimens. In the normal kidney, proximal convoluted tubule, thin and thick segment of Henle's loop, convoluted tubule and collecting tubule were characterized morphologically. The brush border extensions of the proximal tubular epithelium do not seem to absorbe some particular substances from the tubular lumen, but to facilitate the process of absorption by providing the increased membrane area to which these substances can be absorbed. The small vesicular structures in the apical region of the cells indicate the cross sections of the tubular invaginations which are connected with the spaces between brush border extensions, and further with the tubular lumen. These structures are concerned directly with intake of some material (i. e. such as protein) in the tubular epithelial cells, suggesting the menbrane flow mechanism (as reported by Bennet) for pinocytosis of these tubular epithelial cells. Vacuole-, granule- and cytosome-like structures are differentiated in the proximal tubular cells. These cytoplasmic structures are all regarded as the developed forms of the tubular invaginations which directly help intracytoplasmic transport or metabolism of the pinocytosed materials. Basal intussusception (Peace) or basal infolding (Rhodin) is located in the basal region of the tubular epithelial cells, and is characteristically developed in the proximal tubular cells. Although many investigators regarded this structure to be composed of interdigitation of basal cytoplasmic lamellae of adjoining cells, the author is of opinion that some are intracytoplasmic menbrane structures of own cell. The author classified the tubular epithelial cells of proximal convolution into 8 kinds in 4 types, according to their morphological characteristics. 1) Type A : Cells which keep tightly packed brush border extensions in order, fully developd basal infoldings, abundant mitochondria, endoplasmic reticulum and cytoplasmic granules. They are observed chiefly in normal and elapsed cases of acute glomerulonephritis and in mild cases of subchronic glomerulonephritis, and are regarded as the highly energy-reserved form. 2) Type B-I : Cell, which have swollen cytoplasm; the cytoplasmic structures such as vesicles, mitochondria and endoplasmic reticula are decreased in number, brush border extensions often disappeared in these apical regions. However, destruction of the cell membrane is never seen. 3) Type B-II : Cells, which have increased cytosomes or vacuolar structures, abundant but irregularly disposed intracytoplasmic structures such as mitochondria, basal infoldings and other forms. 4) Type B-III : Cells, which have characteristically enlarged basilar extracytoplasmic spaces inside the basement membrane. Increase of intracytoplasmic vacuolar structures depresses the residual cytoplasm. Each cell of B-type is considered to be engaged vigorously in such activities as intracytoplasmic metabolism or transport across the cell. Cells of type B-I and B-II are observed numerously in elapsed cases of acute glomerulonephritis, and in mild cases of subchronic glomerulonephritis, but rarely in the cases of chronic glomerulo-nephritis. Cells of type B-III are noticed frequently in elapsed cases of acct e glomerulonephritis. Type C-I : Cells with partially destroyed membrane. Some of cytoplasmic elements such as mitochondria, cytoplasmic granules, vesicles and endoplasmic reticula, as well as a part of brush border extensions are discharged into the tubular lumen. Type C-II : Cells more severely destroyed than those of type C-I. Occasionally, the great part of cytoplasm with its cytoplasmic elements is carried away into the lumen, whereas the basement membrane is exposed directly to the lumen. These destroyed cells are always accompanied