小鼠短髓襻肾单位在外髓的分布

目的 肾外髓间质渗透梯度形成的机制与髓襻上皮转运功能及其毗邻关系有密切关系，本研究拟建立短髓袢肾单位在外髓的走行规律。方法C57/BL/6J小鼠3只，灌流固定后取肾组织块并树脂812包埋，垂直肾长轴连续半薄切片，从肾被膜到内外髓交界处，共得到1 200张2.5μm厚的连续切片，显微镜下获取数字图像，计算机配准，C语言编程，进而追踪来自皮质浅层和中层的120个短髓襻肾单位。结果 短髓襻肾单位的53%起于肾皮质外1/3，47%起于中间肾皮质。前者髓襻襻曲分布在外髓内带中部同一水平，其襻曲或完全由细段上皮构成，或由髓襻降支细段上皮与升支粗段上皮移行构成；来自中间皮质的短髓襻襻曲位于外髓内带内侧1/2的不同水平，其深度与其肾小球在中间皮质的深度成正比。其襻曲由髓襻升支粗段上皮构成，并在襻曲前构成约50~450μm长的髓襻降支。最深的襻曲在外髓内带弯曲走行。结论髓袢襻曲在外髓的位置及上皮类型不同，提示外髓不同区域的小管对超滤液重吸收的成分也有所区别，对外髓深部渗透梯度增高的形成产生一定的影响；而襻曲的位置和上皮构成与肾小球在皮质的位置相关，提示肾小球的滤过与肾小管的重吸收功能有整体的调节。

Distribution of the mouse short loop nephron in outer medulla

Objective The regulatory mechanism of formation of the countercurrent multiplier in the outer medulla of the kidney is very complex,which has close relation with the epithelial transport and the spatial arrangement of the Henle,s loops and vessels.The objective of the present study was to investigate the tubular course of the short loop nephrons (SLN)in outer medulla. Methods Three C57/BL/6J mice were fixed by perfusion and embedded in Epon 812.Tissue blocks were cut perpendicular to the longitudinal axis of the kidney. A total of 1 200,2.5-μm-thick serial sections were obtained from the surface to the transition of the inner medulla and the outer medulla.After image recordings and alignment, 120 SLN originated from the superficial cortex and mid-cortex were traced and 3D-reconstructed with a series of computer programs written in C. Results SLN (53%) derived from the superficial cortex had their loop bends located at nearly the same level in the middle part of the inner strip of the outer medulla(ISOM). The bend was covered entirely by descending thin limb epithelium whereas SLN(47%) derived from the middle cortex had their loop bends located in various levels in the inner half part of the inner strip of the outer medulla,and the loop bend was covered with the thick ascending limb epithelium.The thick ascending limb epithelium also covered various distances in the descending limb to form a pre-bend segment with about 50-450 μm long.The deepest bend reached the boundary of the outer and inter medulla,where the loop ran winding. Conclusion The difference of both distribution and the epithelium of loop bends in ISOM suggests the differential reabsorption in ultra filtration composition in different levels in ISOM,which may contribute the formation the increase osmotic gradient in ISOM.In addition,the finding that both distribution and the epithelium of the loop bend are associated with corresponding glomeruli suggests that there may be a systemic regulation between the filtration of glomerul