UREA TRANSPORT AND THE URINARY CONCENTRATING MECHANISM

离体肾上皮细胞的研究和数学建模研究是 正在进行的研究尿素在浓缩中的作用， 机制，并确定内部集中的机制 髓质 发现内髓集合管为异质性 关于URFEA渗透性。 从外三分之一处收集管道 内髓质的细胞对尿素的渗透性较低， 髓射线和外髓。 与此相反， 内髓集合管的内部三分之二具有极 对尿素的高渗透性，40 x 10-5 cm/s。 这种集合管的模式 尿素渗透性使髓内轴向尿素梯度最大化 通过将尿素吸收延迟到乳头尖端附近， 血流量最低。 发现乳头状表面上皮具有 对尿素的渗透性低（1 x 10-5 cm/s），表面积相对较小 内髓集合管。 结果表明，尿素转运 乳头状上皮细胞之间的相互作用不太可能对 尿素输送到内部髓腔。

Studies of isolated renal epithelia and mathematical modelling studies are being carried out to investigate the role of urea in the concentrating mechanism and to define the mechanism of concentration in the inner medulla. The inner medullary collecting duct was found to be heterogenous with respect to urfea permeability. Collecting ducts from the outer third of the inner medulla have a low permeability to urea like those from the medullary rays and outer medulla. In contrast, collecting ducts from the inner two-thirds of the inner medullary collecting duct have an extremely high permeability to urea, 40 x 10-5 cm/s. This pattern of collecting duct urea permeabilities maximizes the axial urea gradient in the inner medulla by delaying urea absorption to near the papillary tip where the effective blood flow is lowest. The papillary surface epithelium was found to have a low permeability to urea (1 x 10-5 cm/s) and a small surface area relative to inner medullary collecting ducts. It is concluded that urea transport across the papillary epithelium is unlikely to contribute significantly to urea delivery to the inner medullary interstitium.