第三节 肾小管与集合管的重吸收 Reabsorption in the renal tubule and collecting duct,超滤液量(ultrafiltrate volume)180L /日 ； 尿量(urine volume)1.5L /日； 提示99%被重吸收 , 1%排出体外； 某物质的终尿浓度u ， 血浆浓度P； u/p反映物质被重吸收或分泌的情况； 因为水的重吸收量达99%，流量缩小了100倍， 所以u/p=100的物质既不被重吸收又不被分泌和排泄； u/p100如肌酐(creatinine)等，提示肾小管还有分泌和排泄功能；,重吸收部位:,近球小管(proximal tubule)：14mm； 刷状缘(brush border)：增大重吸收面积 髓袢(Henles loop) :210mm 远球小管(distal tubule) : 13.6mm 集合管(collecting duct) : 20mm,一、重吸收的方式,1.被动重吸收(passive transport)：指小管液中的水和溶质依借电化学差通过肾小管上皮细胞进入细胞外液的过程。 Water and solutes are transported across the tubular epithelial cells into the extracellular fluid that is mediated by electronic and chemical forces. 水借渗透压(osmotic forces)之差被动重吸收，渗透压差是其动力。 溶质浓度差(difference of concentration)和电位差(difference of potential)（电化学差）是其被动重吸收的动力。,2.主动重吸收(active transport)：指肾小管上皮细胞逆电化学差，将小管内溶质主动转运到小管外组织间液的过程。 Active transport can move a solute against an electrochemical gradient and requires energy derived from metabolism. 逆浓度差 逆电位差,髓袢升支粗段(thick segment of ascending limb) ：继发性主动转运(secondary active transport) 特点：逆电化学差、耗能 Characteristics: against an electrochemical gradient and requires energy 葡萄糖(glucose)、氨基酸(amino acid)、Na+等主动重吸收,二、几种物质的重吸收,1、Na+的重吸收： 方式主动重吸收(active transport) 原尿(glomerular filtrate) Na+ 500g /日； 终尿(urine) Na+ 35g /日 ， 99%回收； 地点和吸收比例： 近球小管：占滤过量6570%； 髓袢：20%； 远曲小管：10%； 集合管：耗O2 1克，重吸收Na+ 2030克主动转运；,近球小管前半段： Na+与GS、氨基酸同向转运(symport) 主动重 吸收 Na +与H + 逆向转运(antiport) (active transport) 近球小管后半段： Na+、Cl- 细胞旁路被动重吸收(paracellular pathway),各段小管重吸收Na+ 的机制 近球小管(Proximal tubule),近球小管泵漏模式 (pump-leak model),A.首先小管腔Na+顺浓度差扩散入小管细胞内 There is a concentration gradient favoring sodium diffusion into the cell. B.细胞侧膜的钠泵将其泵入细胞间隙 The cell has sodium pump to transport sodium out of the cell into the interstitium. C.水因渗透压被吸引到间隙，造成间隙内静水压升高 Water moves to the interstitium by osmosis , and it leads to a high level of hydrostatic pressure in interstitium.,D.静水压升高引起Na+和水通过基膜进入细胞间 液和相邻毛细血管，并有回漏现象. Sodium and water are reabsorbed from the interstitial fluid into the peritubular capillaries by hydrostatic pressure , meanwhile ,there also exits leakage from interstitial fluid to tubule. E.在Na+被重吸收时，尚有相当量的负离子 (HCO3- 或Cl-)顺Na+被重吸收时造成的电位差而 被重吸收。 Many negative ions are reabsorbed by difference of potential induced by the process of sodium reabsorption .,远曲小管：Na+重吸收量少 A.紧密连接(tight junctions)对Na+通透性低，回漏量少； B.管内外浓度差大，电位差大； 20 mf T/L : 140mfT/L；管内-1045 mV C.管腔膜(luminal membrane)和管周膜(basolateral membrane)分布有Na+泵(sodium pump)，可将Na+泵到细胞外液和毛细血管内； D.伴有负离子重吸收和Na+ -H+ 、Na+-K+交换；,髓袢(Henles loop)：主动转运 与（继发性主动转运；secondary active transport) 升支粗段被动转运相结合。 集合管(connecting tubule)：主动转运，Na+重吸收造成管内-35mV，机制未明。,Cl-,2. Cl-的重吸收：,大部分是伴随Na+的主动重吸收而被动重吸收。 When sodium is reabsorbed through the tubular epithelial cell, negative ions such as chloride are transported passively along with sodium. 各段小管重吸收Cl-的机制： 近球小管(proximal tubule)：管内负电位是Na+依赖性;,A. Na+的主动重吸收形成小管内外电位差，管内-4mV； Sodium is positively reabsorbed from the tubule. This creates a difference of potential. B. 负离子HCO3-、Cl-顺电位差被动重吸收; Negative ions such as HCO3-、Cl- are passively reabsorbed by difference of potential. C. HCO3-比Cl-优先重吸收，加上渗透压差导致水的重吸收 小管液中Cl-浓度 ； Preferential reabsorption of HCO3- and the reabsorption of water by osmosis pressure lead to a high concentration of chloride in tubule. D.Cl-的管内外浓度差又造成Cl-被动重吸收； Cl- is reabsorbed passively by the difference of concentration.,髓袢升支粗段，管腔内正电位（+2+10mV）,正电位依赖Cl-、K+存在。 Na+、Cl-、K+由同一载体协同转运。 Movement of sodium across the luminal membrane is mediated primarily by a 1-sodium,2-chloride,1-potassium cotransporter. 用哇巴因(-) 钠泵，转运受阻，提示Na+泵参与此过程，机制可能如下： The transport is blocked by using ouabain which blocks the activity of sodium pump.,A.升支粗段上皮细胞管周膜的Na+泵将Na+由胞内泵向组织间液; Sodium is transported from the epithelial cell into interstitial fluid by the activity of sodium pump in the epithelial cell basolateral membranes. B. Na+被泵出后，细胞内Na+ ，出现管腔内与细胞内Na+浓度差; Sodium pump maintains a low intracellular sodium concentration.,C.管腔内Na+顺此浓度差扩散到细胞内，但须与Cl-、K+由同一载体协同转运。Na+:2Cl-:K+ The low intracellular sodium concentration in turn provides a favorable gradient for movement of sodium from the tubular fluid into the cell. In the thick ascending loop, movement of sodium across the luminal membrane is mediated by a 1-sodium,2-chloride,1-potassium cotransporter.,D.进入细胞后： Na+经Na+泵泵到组织间液; Na+ is transported to interstitial fluid by sodium pump Cl-顺浓度差经管周膜扩散到组织间液 ； Cl- diffuses into interstitial fluid through basolateral membrane. K+由于浓度差经管腔膜返回管腔内； K+ returns to tubule through basolateral membrane by difference of concentration.,E.由于Cl-进入组织间液多，K+返回管腔内液多， 造成管腔内正电位; 特点： Na+主动转运(active transport)， Cl-继发性主动转运(secondary active transport) 速尿(furosedon)、利尿酸(-)(crinuryl),3.水的重吸收：,99%重吸收，1%排出体外； 水的重吸收： 在近球小管重吸收：伴随溶质而重吸收，与体内是否缺水无关。 In proximal tubule , the reabsorption of water is accompanied with the reabsorption of solutes. 在远曲小管和集合管重吸收：吸收量受调节，体内缺水时重吸收多，体内不缺水时重吸收少。 In distal tubule and collecting duct water reabsorption is regulated by t