Stratified laminae fenestratae (alveolus fenestratus endothelialis) in the glomerular capillaries of the mouse kidney.

The fine structure of the stratified lamina fenestrata of the mouse glomerulus was described in detail in both transmission and scanning electron microscopy. We propose to name the extremely developed structure of the stratified lamina fenestrata as the alveolus endothelialis. It consists of numerous small irregular spaces partitioned by thin cytoplasmic processes. Individual spaces communicate with each other through the fenestra surrounded by the cytoplasmic partitions. This structure occurs not only on the basal lamina but also on the perikaryal portion of the endothelium. The constant appearance of the alveolus fenestratus without association of any pathological or degenerative changes suggests that this structure represents a certain general and fundamental feature of the fenestrated endothelial cell. Possible mechanisms for the genesis of this structure are briefly discussed.