The glomerular vascular pole is the gate for the afferent and efferent arterioles and mesangial cells and a frequent location of peripolar cells with an unclear function. It has been studied in definitive detail for >30 years, and functionally interrogated in the context of signal transduction from the macula densa to the mesangial cells and afferent arteriolar smooth muscle cells from 10 to 20 years ago. Two recent discoveries shed additional light on the vascular pole, with possibly far-reaching implications. One, which uses novel serial section electron microscopy, reveals a shorter capillary pathway between the basins of the afferent and efferent arterioles. Such a pathway, when patent, may short-circuit the multitude of capillaries in the glomerular tuft. Notably, this shorter capillary route is enclosed within the glomerular mesangium. The second study used anti-Thy1.1–induced mesangiolysis and intravital microscopy to unequivocally establish in vivo the long-suspected contractile function of mesangial cells, which have the ability to change the geometry and curvature of glomerular capillaries. These studies led me to hypothesize the existence of a glomerular perfusion rheostat, in which the shorter path periodically fluctuates between being more and less patent. This action reduces or increases blood flow through the entire glomerular capillary tuft. A corollary is that the GFR is a net product of balance between the states of capillary perfusion, and that deviations from the balanced state would increase or decrease GFR. Taken together, these studies may pave the way to a more profound understanding of glomerular microcirculation under basal conditions and in progression of glomerulopathies.

肾小球血管极是传入和传出小动脉和系膜细胞的门户，也是功能尚不清楚的周极细胞的常见位置。人们对其进行了超过 30 年的明确详细研究，并在 10 至 20 年前在从致密斑到系膜细胞和传入小动脉平滑肌细胞的信号转导背景下对其进行了功能性研究。最近的两项发现为血管极提供了更多线索，可能具有深远的影响。其中一种使用新型连续切片电子显微镜，揭示了传入和传出小动脉盆地之间较短的毛细血管通路。当这种通路通畅时，可能会使肾小球簇中的大量毛细血管短路。值得注意的是，这种较短的毛细血管路径被封闭在肾小球系膜内。第二项研究使用抗 Thy1.1 诱导的肾小球系膜溶解和活体显微镜检查，在体内明确建立了长期以来人们怀疑的系膜细胞的收缩功能，这些细胞能够改变肾小球毛细血管的几何形状和曲率。这些研究使我推测肾小球灌注变阻器的存在，其中较短的路径在更多和更少的专利之间周期性地波动。这一作用减少或增加了通过整个肾小球毛细血管簇的血流量。推论是 GFR 是毛细血管灌注状态之间平衡的净乘积，偏离平衡状态会增加或减少 GFR。总而言之，这些研究可能为更深入地了解基础条件下的肾小球微循环和肾小球疾病进展铺平道路。