肾小球系膜(mesangium、系膜、环间膜)是与毛细管相关联的结构位于肾脏的肾小球。连续着小动脉的平滑肌。位于毛细管腔(Lumen (anatomy))的外部，但被整个"毛细管集群"围绕。它是在毛细管(angis)集群的中间位置(meso)。被"鲍氏囊的基底膜"(基底层)包含着，而此基底层围绕着毛细管及肾小球系膜。

这个术语经常与系膜细胞(mesangial cell)互换使用，但在这种情况下具体指的是肾小球内系膜细胞(intraglomerular mesangial cell)。这些细胞是吞噬细胞及分泌被称为"系膜基质"(mesangial matrix)的无定形"类基底膜"物质。它们通常地从毛细管内皮细胞的管腔分离开来。

In the glomerulus of the kidney, the mesangium is a structure associated with the capillaries. It is continuous with the smooth muscles of the arterioles. It is outside the capillary lumen, but surrounded by capillaries. It is in the middle (meso) between the capillaries (angis). It is contained by the basement membrane, which surrounds both the capillaries and the mesangium.