Urine-Concentrating Mechanism in the Inner Medulla: Function of the Thin Limbs of the Loops of Henle
Urine-Concentrating Mechanism in the Inner Medulla: Function of the Thin Limbs of the Loops of Henle
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DOI：
10.2215/cjn.08750812
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发表时间：
2014-10-01
影响因子：
9.8
通讯作者：
Pannabecker, Thomas L.
中科院分区：
文献类型：
--
作者：
Dantzler, William H.;Layton, Anita T.;Pannabecker, Thomas L.
哺乳动物产生对血浆高渗的尿的能力需要产生从皮髓质交界处到乳头尖端沿髓质沿着增加渗透压的梯度。逆流增殖显然建立了这种梯度的外髓，有大量的跨上皮重吸收的NaCl从水不渗透的厚上升肢体的环的亨乐。然而，这一过程并没有建立更陡峭的渗透梯度内髓，那里没有厚的上升肢体的环的亨勒和水不渗透的上升薄肢体缺乏积极的跨上皮运输的NaCl或任何其他溶质。在髓质内部产生渗透梯度的机制仍然是一个未解之谜，尽管它通常被认为涉及小管和血管中的逆流。通过创建描绘大鼠肾脏中小管和血管及其溶质和水渗透性的三维关系的生理模型以及通过创建数学模型，提出了这些内髓小管和血管之间的三维相互作用在浓缩过程中可能发挥的作用。基于生物现象的模型。当前的数学模型结合了通过明确定义的管状和间质隔室的实验确定或估计的溶质和水流，预测的尿液渗透压与在中度抗利尿大鼠中观察到的结果非常一致。当前模型提供了比先前模型更好的预测;然而，当前模型仍然无法预测最大浓度大鼠的尿液渗透压摩尔浓度。
The ability of mammals to produce urine hyperosmotic to plasma requires the generation of a gradient of increasing osmolality along the medulla from the corticomedullary junction to the papilla tip. Countercurrent multiplication apparently establishes this gradient in the outer medulla, where there is substantial transepithelial reabsorption of NaCl from the water-impermeable thick ascending limbs of the loops of Hen le. However, this process does not establish the much steeper osmotic gradient in the inner medulla, where there are no thick ascending limbs of the loops of Hen le and the water-impermeable ascending thin limbs lack active transepithelial transport of NaCl or any other solute. The mechanism generating the osmotic gradient in the inner medulla remains an unsolved mystery, although it is generally considered to involve countercurrent flows in the tubules and vessels. A possible role for the three-dimensional interactions between these inner medullary tubules and vessels in the concentrating process is suggested by creation of physiologic models that depict the three-dimensional relationships of tubules and vessels and their solute and water permeabilities in rat kidneys and by creation of mathematical models based on biologic phenomena. The current mathematical model, which incorporates experimentally determined or estimated solute and water flows through clearly defined tubular and interstitial compartments, predicts a urine osmolality in good agreement with that observed in moderately antidiuretic rats. The current model provides substantially better predictions than previous models; however, the current model still fails to predict urine osmolalities of maximally concentrating rats.