Madsen K M, Tisher C C
Am J Physiol. 1986 Jun;250(6):F1-15. doi: 10.1152/ajprenal.1986.250.1.F1.
The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (IC), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.
远端小管，包括髓袢升支粗段（TAL）、致密斑和远曲小管（DCT），以及集合管在结构上是异质性的，从而反映出同样存在的功能异质性。随着髓袢升支粗段从髓质向皮质上升，顶端质膜的表面积增加，而基底外侧膜的表面积减小。远曲小管的结构类似于髓质髓袢升支粗段。在远端小管中，结构、钠钾ATP酶活性和氯化钠重吸收能力之间存在良好的相关性。集合管分为初始集合小管（IC）、皮质集合管（CCD）、外髓集合管（OMCD）和内髓集合管（IMCD）。在远端小管和集合管之间是一个过渡区域，称为连接段或连接小管（CNT）。在集合管内的两个主要细胞群体，即闰细胞和主细胞中，存在相当大的结构异质性。在连接小管、初始集合小管和皮质集合管中，钾负荷和盐皮质激素刺激钠钾ATP酶活性，并导致连接小管细胞和主细胞基底外侧膜增殖，从而确定这些区域中负责盐皮质激素刺激钾分泌的细胞。最后，至少存在两种形态上不同的闰细胞群体，即A型和B型。在大鼠中，A型在连接小管和外髓集合管中占主导地位，并且至少在外髓集合管中被认为负责氢离子分泌。B型在皮质集合管中占主导地位，可能参与碳酸氢盐分泌。
