Dept. of Mathematics, Duke University, Durham, NC 27708-0320, USA.
Am J Physiol Renal Physiol. 2012 Apr 1;302(7):F830-9. doi: 10.1152/ajprenal.00539.2011. Epub 2011 Dec 7.
Recent anatomic findings indicate that in the upper inner medulla of the rodent kidney, tubules, and vessels are organized around clusters of collecting ducts (CDs). Within CD clusters, CDs and some of the ascending vasa recta (AVR) and ascending thin limbs (ATLs), when viewed in transverse sections, form interstitial nodal spaces, which are arrayed at structured intervals throughout the inner medulla. These spaces, or microdomains, are bordered on one side by a single CD, on the opposite side by one or more ATLs, and on the other two sides by AVR. To study the interactions among these CDs, ATLs, and AVR, we have developed a mathematical compartment model, which simulates steady-state solute exchange through the microdomain at a given inner medullary level. Fluid in all compartments contains Na(+), Cl(-), urea and, in the microdomain, negative fixed charges that represent macromolecules (e.g., hyaluronan) balanced by Na(+). Fluid entry into AVR is assumed to be driven by hydraulic and oncotic pressures. Model results suggest that the isolated microdomains facilitate solute and fluid mixing among the CDs, ATLs, and AVR, promote water withdrawal from CDs, and consequently may play an important role in generating the inner medullary osmotic gradient.
最近的解剖学发现表明，在啮齿动物肾脏的内髓内层，肾小管和血管围绕着集合管（CD）簇组织。在 CD 簇内，CD 以及一些升支直小血管（AVR）和升支细段（ATL），在横切面上观察时，形成了间质节结空间，这些空间在整个内髓以有序的间隔排列。这些空间或微域，一侧由单个 CD 围成，另一侧由一个或多个 ATL 围成，另外两侧由 AVR 围成。为了研究这些 CD、ATL 和 AVR 之间的相互作用，我们开发了一个数学室模型，该模型模拟了给定内髓水平下通过微域的溶质稳态交换。所有室中的流体都含有 Na(+)、Cl(-)、尿素，并且在微域中，代表大分子（例如透明质酸）的负固定电荷由 Na(+)平衡。假定 AVR 中的流体进入是由液压和渗透压力驱动的。模型结果表明，孤立的微域促进了 CD、ATL 和 AVR 之间的溶质和流体混合，促进了 CD 中的水分提取，因此可能在内髓渗透梯度的产生中发挥重要作用。
