Hartley Jordan, Gribbins Kevin M, Siegel Dustin S
Department of Biology, Southeast Missouri State University, Cape Girardeau, Missouri.
Department of Biology, University of Indianapolis, Indianapolis, Indiana.
J Morphol. 2019 Oct;280(10):1452-1461. doi: 10.1002/jmor.21041. Epub 2019 Jul 17.
Salamanders possess kidneys with two distinct regions: a caudal pelvic portion and cranial genital portion. Nephrons of the pelvic region are responsible for urine formation and transport. Nephrons of the genital region transport sperm from testes to Wolffian ducts; however, nephrons of the genital region possess all the same functional regions found in pelvic kidney nephrons that are involved with urine formation and transport (renal corpuscles, proximal tubules, distal tubules, and collecting ducts). Morphological similarities between pelvic and genital regions stimulated past researchers to hypothesize that nephrons of genital kidneys possess dual function; that is, sperm transport and urine formation/transport. Considering size of glomeruli is directly related to the total amount of blood plasma filtered into the Bowman's space, we tested the hypothesis that nephrons of genital kidneys have reduced urine formation function by comparing glomerular size between nephrons of pelvic and genital kidney regions in Eurycea longicauda with general histological techniques. Light microscopy analysis revealed that glomeruli of pelvic kidneys were significantly larger than those measured from genital kidneys. Transmission electron microscopy analysis also revealed modifications in genital kidney nephrons when compared to pelvic kidney nephrons that suggested a decrease in urine formation function in genital kidneys. Such modifications included a decrease in basal and lateral plasma membrane folding in genital kidney proximal and distal tubules compared to that of pelvic kidney proximal and distal tubules. Genital kidney proximal tubules were also ciliated, which was not observed in pelvic kidney proximal tubules. In conclusion, although structurally similar at the histological level, it appears that nephrons of genital kidneys have decreased urine formation function based on glomerular size comparison and nephron ultrastructure.
尾部盆腔部分和头部生殖部分。盆腔区域的肾单位负责尿液的形成和运输。生殖区域的肾单位将精子从睾丸输送到沃尔夫管；然而，生殖区域的肾单位具有与盆腔肾肾单位中参与尿液形成和运输的所有相同功能区域（肾小体、近端小管、远端小管和集合管）。盆腔和生殖区域之间的形态学相似性促使过去的研究人员推测生殖肾的肾单位具有双重功能；也就是说，精子运输和尿液形成/运输。考虑到肾小球的大小与滤入鲍曼间隙的血浆总量直接相关，我们通过使用一般组织学技术比较长尾欧螈盆腔和生殖肾区域肾单位的肾小球大小，来检验生殖肾肾单位尿液形成功能降低的假设。光学显微镜分析显示，盆腔肾的肾小球明显大于从生殖肾测量的肾小球。透射电子显微镜分析还显示，与盆腔肾肾单位相比，生殖肾肾单位存在一些变化，这表明生殖肾的尿液形成功能有所下降。这些变化包括与盆腔肾近端和远端小管相比，生殖肾近端和远端小管基底和侧质膜折叠减少。生殖肾近端小管也有纤毛，而盆腔肾近端小管中未观察到这种情况。总之，尽管在组织学水平上结构相似，但基于肾小球大小比较和肾单位超微结构，生殖肾的肾单位似乎具有降低的尿液形成功能。
