The extraglomerular mesangial cells help with the signalling between macula densa cells and juxtaglomerular cells.

球外系膜细胞辅助致密斑和球旁细胞的信息传递过程。

Macula densa cells are located in the distal convoluted tubule and they can sense when levels of sodium and chloride are low.

致密斑位于远曲小管，可以感受到钠和氯水平降低。

So, in the case of hypovolemia and hypotension, the macula densa cells sense the low sodium and chloride levels and send a signal over to the juxtaglomerular cells which are located in the wall of the afferent arteriole.

因此，当血容量减少、低血压时，致密斑感受到钠、氯含量降低，传递信号给位于入球小动脉血管壁上的球旁细胞。