Ojeda José L, Icardo José M, Wong Wai P, Ip Yuen K
Department of Anatomy and Cell Biology, University of Cantabria, Santander, Spain.
Anat Rec A Discov Mol Cell Evol Biol. 2006 Jun;288(6):609-25. doi: 10.1002/ar.a.20333.
The Dipnoi (lungfishes) have developed true lungs, having the ability to take oxygen from both the gills and the lungs. During the tropical dry season, many lungfish estivate on land, breathing only air. The estivation period is accompanied by profound functional modifications, including the suppression of urine. Thus, the lungfish kidney must be designed to cope with these dramatic cyclic changes in renal function. We study here the microanatomy and the structure of the kidney of the African lungfish Protopterus dolloi, maintained under controlled freshwater conditions. Chemical microdissection, light microscopy, and scanning and transmission electron microscopy have been used. The nephrons of P. dolloi are composed of a renal corpuscle (RC) and of a renal tubule that appears divided into five morphologically distinct segments: neck segment (NS), proximal tubule (PT), intermediate segment (IS), distal tubule (DT), and collecting tubule (CT). Paired CTs abut into a collecting duct, the latter emptying into an archinephric duct. The RCs lie in the mid-zone of the kidney, between the PTs and the convoluted DTs. The spatial distribution of these elements allows recognition of a kidney zonation. The RCs group into clusters (3-4 RCs per cluster) that are supplied by a single arteriole surrounded by pericytes. Each cluster appears to represent a functional unit with a common hemodynamic regulatory mechanism. The major processes of the podocytes form flattened networks that appear to constitute an integrated system due to the presence of gap junctions. The existence of mesangial cells with large cell processes, and of mesangial cells with a dendritic appearance, suggests a complex functional role (contractile and phagocytic) for the mesangium. The NS and the IS are the narrowest nephron segments, formed only by multiciliated cells. The PT and the DT can be subdivided, based on the tubular morphology and on cell composition, into portions I and II: PTI is formed only by brush border (BB) cells, while PTII contains BB and multiciliated cells. The DTI is formed by segment-specific cells, while the DTII contains segment-specific and a small number of flask cells. The CT contains principal and flask cells in a 5:1 ratio. The flask cells adopt two different configurations (with a narrow canaliculus or with a large cavity). The main goal of this study was to disclose specific kidney features that could be related to function, phylogeny, and habitat. In addition, the present results constitute the basis for a study of the morphologic changes that should occur in the kidney of P. dolloi during estivation.
肺鱼目（肺鱼）已发育出真正的肺，具备从鳃和肺两者获取氧气的能力。在热带旱季，许多肺鱼在陆地上夏眠，仅呼吸空气。夏眠期伴随着深刻的功能改变，包括尿液分泌的抑制。因此，肺鱼的肾脏必须设计成能够应对肾功能的这些剧烈周期性变化。我们在此研究在受控淡水条件下饲养的非洲肺鱼多氏原鳍鱼肾脏的微观解剖结构。使用了化学显微解剖、光学显微镜以及扫描和透射电子显微镜技术。多氏原鳍鱼的肾单位由一个肾小体（RC）和一条肾小管组成，该肾小管似乎分为五个形态上不同的节段：颈部节段（NS）、近端小管（PT）、中间节段（IS）、远端小管（DT）和集合小管（CT）。成对的CT汇入一条集合管，后者排入原肾管。肾小体位于肾脏的中区，在近端小管和盘曲的远端小管之间。这些结构的空间分布使得能够识别肾脏分区。肾小体聚集成簇（每簇3 - 4个肾小体），由单个被周细胞包围的小动脉供血。每个簇似乎代表一个具有共同血液动力学调节机制的功能单位。足细胞的主要突起形成扁平网络，由于存在缝隙连接，这些网络似乎构成一个整合系统。存在具有大细胞突起的系膜细胞以及具有树突状外观的系膜细胞，这表明系膜具有复杂的功能作用（收缩和吞噬）。颈部节段和中间节段是最窄的肾单位节段，仅由多纤毛细胞形成。近端小管和远端小管可根据管腔形态和细胞组成细分为I部和II部：近端小管I部仅由刷状缘（BB）细胞形成，而近端小管II部包含刷状缘细胞和多纤毛细胞。远端小管I部由节段特异性细胞形成，而远端小管II部包含节段特异性细胞和少量烧瓶状细胞。集合小管中主细胞和烧瓶状细胞的比例为5:1。烧瓶状细胞呈现两种不同的形态（具有狭窄的小管或具有大的腔）。本研究的主要目的是揭示可能与功能、系统发育和栖息地相关的肾脏特定特征。此外，目前的结果构成了研究多氏原鳍鱼在夏眠期间肾脏应发生的形态变化的基础。
