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1、关于肾小管与集合管的重吸收现在学习的是第1页，共48页超滤液量超滤液量(ultrafiltrate volume)180L/日日 尿量尿量(urine volume)1.5L/日日 提示提示99%被重吸收被重吸收 1%排出体外排出体外某物质某物质 终尿浓度终尿浓度u/血浆浓度血浆浓度P 反映物质被重吸收或分泌的情况反映物质被重吸收或分泌的情况因为水的重吸收量达因为水的重吸收量达99%，流量缩小了，流量缩小了100倍，倍，所以所以u/p=100的物质既不被重吸收又不被分泌和排泄的物质既不被重吸收又不被分泌和排泄u/p100如肌酐如肌酐(creatinine)等，提示肾小管还有分泌和等，提示肾小管
2、还有分泌和排泄功能排泄功能现在学习的是第2页，共48页重吸收部位重吸收部位:近近球球小小管管(proximal tubule)14mm,刷刷状状缘缘(brush border)增大重吸收面积增大重吸收面积髓袢髓袢(Henles loop)210mm远球小管远球小管(distal tubule)13.6mm集合管集合管(collecting duct)20mm现在学习的是第3页，共48页一、重吸收的方式一、重吸收的方式1.被被动动重重吸吸收收(passive transport)：指指小小管管液液中中的的水水和和溶溶质质依依借借电化学差通过肾小管上皮细胞进入细胞外液的过程。电化学差通过肾小管上皮
3、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.水水借借渗渗透透压压(osmotic forces)之之差差被被动动重重吸吸收收，渗渗透透压压差差是是其动力。其动力。溶溶质质浓浓度度差差(difference of concentration)和和电电位位差差(difference of potential)（电化学差）是
4、其被动重吸收的动力。（电化学差）是其被动重吸收的动力。现在学习的是第4页，共48页浓度差浓度差 电位差电位差 Na+Na+主动主动 Na+Na+H2O Cl-Cl _ 尿素尿素 尿素被动扩散尿素被动扩散 现在学习的是第5页，共48页2.主主动动重重吸吸收收(active transport)：指指肾肾小小管管上上皮皮细细胞胞逆逆电电化化学学差差，将将小小管管内内溶溶质质主主动动转转运到小管外组织间液的过程。运到小管外组织间液的过程。Active transport can move a solute against an electrochemical gradient and require
5、s energy derived from metabolism.逆浓度差逆浓度差逆电位差逆电位差现在学习的是第6页，共48页髓髓袢袢升升支支粗粗段段(thick segment of ascending limb)继继发性主动转运发性主动转运(secondary active transport)特点：逆电化学差特点：逆电化学差 耗能耗能 Characteristics:against an electrochemical gradient and requires energy)葡葡萄萄糖糖(glucose)、氨氨基基酸酸(amino acid)、Na+等等主主动重吸收动重吸收现在学习的是
6、第7页，共48页二、几种物质的重吸收二、几种物质的重吸收1.Na+的重吸收：的重吸收：方式方式主动重吸收主动重吸收(active transport)原尿原尿(glomerular filtrate)Na+500g/日，日，终尿终尿(urine)Na+35g/日日 99%回收回收地点和吸收比例地点和吸收比例：近球小管：占滤过量近球小管：占滤过量6570%远曲小管：远曲小管：10%髓袢：髓袢：20%集合管：耗集合管：耗O2 1克，重吸收克，重吸收Na+2030克克主动转运主动转运现在学习的是第8页，共48页各段小管重吸收各段小管重吸收Na+的机制的机制近球小管近球小管Proximal tubul
7、e近球小管前半段：近球小管前半段：Na+与与GS、氨基酸同向转运氨基酸同向转运(symport)主动重吸收主动重吸收(active transport)Na+与与H+逆向转运逆向转运(antiport)现在学习的是第9页，共48页近球小管后半段：近球小管后半段：Na+、Cl-细胞旁路被动重吸收细胞旁路被动重吸收(paracellular pathway)。现在学习的是第10页，共48页现在学习的是第11页，共48页近球小管近球小管泵漏模式泵漏模式(pump-leak model)A 首先小管腔首先小管腔Na+顺浓度差扩散入小管细胞内顺浓度差扩散入小管细胞内There is a concentr
8、ation gradient favoring sodium diffusion into the cell.B 细胞侧膜的钠泵将其泵入细胞间隙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 hydrostat
9、ic pressure in interstitium.现在学习的是第12页，共48页D 静静水水压压升升高高引引起起Na+和和水水通通过过基基膜膜进进入入细细胞胞间间液和相邻毛细血管，并有回漏现象液和相邻毛细血管，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
10、.E 在在Na+被被重重吸吸收收时时，尚尚有有相相当当量量的的负负离离子子（HCO3-或或ClCl-）顺顺Na+被被重重吸吸收收时时造造成成的的电电位位差而被重吸收。差而被重吸收。Many negative ions are reabsorbed by difference of potential induced by the process of sodium reabsorption.现在学习的是第13页，共48页远曲小管：远曲小管：Na+重吸收量少重吸收量少A 紧密连接紧密连接(tight junctions)对对Na+通透性低，回漏量少通透性低，回漏量少B 管内外浓度差大，电位差大管
11、内外浓度差大，电位差大 20mfT/L:140mfT/L 管内管内-1045 mVC 管管腔腔膜膜(luminal membrane)和和管管周周膜膜(basolateral membrane)分分布布有有Na+泵泵(sodium pump)，可可将将Na+泵泵到到细细胞胞外外液液和和毛毛细细血管内血管内D 伴有负离子重吸收和伴有负离子重吸收和Na+-H+、Na+-K+交换交换现在学习的是第14页，共48页髓髓袢袢(Henles loop)：主主动动转转运运与与ClCl-继继发发性性主主动动转转运运(secondary active transport)升升支支粗粗段段被动转运相结合。被动转运
12、相结合。集集合合管管(connecting tubule)：主主动动转转运运，Na+重吸收造成管内重吸收造成管内-35-35mVmV。机制未明机制未明现在学习的是第15页，共48页2.ClCl-的重吸收：的重吸收：大部分是伴随大部分是伴随Na+的主动重吸收而被动重吸收。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.各段小管重吸收各段小管重吸收C
13、lCl-的机制：的机制：近近球球小小管管(proximal tubule)：管管内内负负电电位位是是Na+依依赖赖性性现在学习的是第16页，共48页A Na+的主动重吸收形成小管内外电位差，管内的主动重吸收形成小管内外电位差，管内-4-4mVmV Sodium is positively reabsorbed from the tubule.This creates a difference of potential.B 负离子负离子HCO3-、ClCl-顺电位差被动重吸收顺电位差被动重吸收 Negative ions such as HCO3-、ClCl-are passively reab
14、sorbed by difference of potential.C HCO3-比比ClCl-优优先先重重吸吸收收，加加上上渗渗透透压压差差导导致致水水的重吸收的重吸收 小管液中小管液中ClCl-浓度浓度 Preferential reabsorption of HCO3-and the reabsorption of water by osmosis pressure lead to a high concentration of chloride in tubule.D Cl Cl-的管内外浓度差又造成的管内外浓度差又造成ClCl-被动重吸收被动重吸收 Cl-is reabsorbed
15、passively by the difference of concentration.现在学习的是第17页，共48页髓髓袢袢升升支支粗粗段段，管管腔腔内内正正电电位位（+2+2+10+10mVmV）现在学习的是第18页，共48页正电位依赖正电位依赖ClCl-、K K+存在。存在。NaNa+、ClCl-、K K+由同一载体协同转运。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.用用
16、哇哇巴巴因因(-)(-)钠钠泵泵，转转运运受受阻阻，提提示示NaNa+泵泵参参与与此此过程，机制可能如下：过程，机制可能如下：The transport is blocked by using ouabain which blocks the activity of sodium pump.现在学习的是第19页，共48页A 升升支支粗粗段段上上皮皮细细胞胞管管周周膜膜的的NaNa+泵泵将将NaNa+由胞内泵向组织间液由胞内泵向组织间液 Sodium is transported from the epithelial cell into interstitial fluid by the ac
17、tivity of sodium pump in the epithelial cell basolateral membranes.B NaNa+被被泵泵出出后后，细细胞胞内内NaNa+，出出现现管管腔内与细胞内腔内与细胞内NaNa+浓度差浓度差 Sodium pump maintains a low intracellular sodium concentration.现在学习的是第20页，共48页C C 管管腔腔内内NaNa+顺顺此此浓浓度度差差扩扩散散到到细细胞胞内内，但但须须与与ClCl-、K K+由由同同一一载载体体协协同同转转运运。NaNa+:2Cl:2Cl-:K:K+The l
18、ow 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.现在学习的是第21页，共48页D 进入细胞后，进入细
19、胞后，Na+经经Na+泵泵到组织间液泵泵到组织间液 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.现在学习的是第22
20、页，共48页E 由由于于Cl-进进入入组组织织间间液液多多，K+返返回回管管腔腔内液多，造成管腔内正电位内液多，造成管腔内正电位特特点点：Na+主主动动转转运运(active transport)，Cl-继继发发性性主主动动转转运运(secondary active transport)速速尿尿(furosedon)、利尿酸、利尿酸(-)(crinuryl)现在学习的是第23页，共48页3.3.水的重吸收：水的重吸收：99%99%重吸收，重吸收，1%1%排出体外排出体外水的重吸收：水的重吸收：在在近近球球小小管管重重吸吸收收，伴伴溶溶质质而而重重吸吸收收，与与体体内内是是否否缺缺水水无关无关I
21、n proximal tubule,the reabsorption of water is accompanied with the reabsorption of solutes.在在远远曲曲小小管管和和集集合合管管吸吸收收，吸吸收收量量受受调调节节，体体内内缺缺少少水时重吸收多，体内不缺水时重吸收少。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 the condition of body.现在学习的是第24页，共48页 近球小管近球小管656570%70%
22、水在各段小管水在各段小管 髓袢髓袢 10%10%重吸收比例重吸收比例 远曲小管远曲小管 10%10%集合管集合管 10 1020%20%近近球球小小管管管管壁壁对对水水通通透透性性高高，高高远远曲曲小小管管34倍倍，是是一一种种等渗重吸收。等渗重吸收。In proximal tubule，the process of water reabsorption is isosmotic because the permeability of tubule to water is high.髓髓袢袢、远远曲曲小小管管集集合合管管对对水水的的重重吸吸收收机机制制，见见尿尿液液浓浓缩缩与稀释。与稀释。现在
23、学习的是第25页，共48页4.HCO3-的的重吸收重吸收特特点点：肾肾小小管管重重吸吸收收HCO3-是是以以CO2的的形形式式而而非非直直接接以以HCO3-的的形形式式进进行行，回回到到血血中中的的HCO3-是是由由细细胞胞产产生生，并并非非小小管管液液中的中的HCO3-。HCO3-is reabsorbed as a gas form.HCO3-比比Cl-优先重吸收，是因为优先重吸收，是因为CO2能迅速透过管腔膜。能迅速透过管腔膜。现在学习的是第26页，共48页5.K+的重吸收：的重吸收：滤过液滤过液35克克/日，终尿日，终尿24克克/日日主细胞重吸收主细胞重吸收Na+和水和水,分泌分泌K+
24、。闰细胞则主要分泌。闰细胞则主要分泌H+。The principal cells reabsorb sodium and water and secrete potassium;the intercalated cells secrete hydrogen.特特点点：滤滤过过液液中中的的K+绝绝大大部部分分被被重重吸吸收收（在在近近球球小小管管），终终尿尿中中的的K+主要是由远曲小管和集合管分泌。主要是由远曲小管和集合管分泌。Almost all potassium in proximal tubule is reabsorbed,and the potassium in urine is m
25、ostly secreted by distal tubule and collecting duct.近球小管管腔内近球小管管腔内-4-4mVmV，K K+重吸收逆电位差主动重吸收。重吸收逆电位差主动重吸收。现在学习的是第27页，共48页6.6.葡萄糖的重吸收：葡萄糖的重吸收：A 逆浓度差主动重吸收逆浓度差主动重吸收B 借助借助Na+的主动重吸收而继发主动重吸收的主动重吸收而继发主动重吸收C 与刷状缘载体蛋白有关，协同转运与刷状缘载体蛋白有关，协同转运D 胞内葡萄糖通过管周膜进入组织间液的过程是易化扩散胞内葡萄糖通过管周膜进入组织间液的过程是易化扩散。A specific carrier p
26、rotein in the brush border combines with a sodium ion and a glucose molecule at the same time.The transport mechanism is so efficient that it removes virtually all the glucose from the tubular lumen.After entry into the cell,glucose exits across the basolateral membranes by facilitated diffusion,dri
27、ven by the high glucose concentration in the cell.现在学习的是第28页，共48页肾肾糖糖阈阈(renal glucose threshold)：当当血血中中葡葡萄萄糖糖浓浓度度160160180180mg%mg%时时，超过部分肾小管重吸收葡萄糖的能力，出现尿糖超过部分肾小管重吸收葡萄糖的能力，出现尿糖。When the concentration of glucose in blood is above 160180mg%,a small amount of glucose begins to appear in the urine.葡葡萄萄糖
28、糖吸吸收收极极限限量量(transport maximum)：当当血血糖糖浓浓度度增增高高到到令令全全部部肾肾小小管管对对糖糖重重吸吸收收的的能能力力到到达达极极限限时时，此此值值叫叫。（男男375375mg/minmg/min，女女300300mg/minmg/min）The overall transport maximum for the kidneys is reached when all nephrons have reached their maximal capacity to reabsorb glucose.E 如近球小管对如近球小管对Na+重吸收重吸收 ，葡萄糖吸收极限量
29、也，葡萄糖吸收极限量也 。现在学习的是第29页，共48页7.其它物质重吸收：其它物质重吸收：氨基酸氨基酸同葡萄糖同葡萄糖 HPO4、SO4与与NaNa+伴联伴联现在学习的是第30页，共48页第三节第三节 肾小管与集合管肾小管与集合管的分泌和排泄的分泌和排泄肾小管分泌肾小管分泌(tubular secretion)：指小管上皮细胞指小管上皮细胞通过新陈代谢，将它所产生的物质分泌通过新陈代谢，将它所产生的物质分泌到小管液中去的过程。到小管液中去的过程。肾肾小小管管排排泄泄(tubular excretion)：指指肾肾小小管管上上皮皮细细胞胞将将血血液液中中某某些些物物质质直直接接排排到到小小管管
30、中中去的过程。去的过程。现在学习的是第31页，共48页1.H+的分泌的分泌H+的产生：的产生：CO2+H2O H2CO3 HCO3-+H+H+-Na-Na+交交换换，方方向向相相反反,叫叫逆逆向向交交换换(counter-transport)H+分分泌泌到到小小管管液液中中，主主要要在在近近球球小小管管发发生。生。现在学习的是第32页，共48页远远曲曲小小管管和和集集合合管管：除除H+-Na-Na+交交换换外外，还还有有K+-NaNa+交交换换，两两者者相相互互抑抑制制，当当酸酸中中毒毒时时H+，H+-Na-Na+交交换换加加强强，K+-Na-Na+交交换换 ，或或造造成成血血K+，反过来用乙
31、酰唑胺反过来用乙酰唑胺(-)碳碳酸酸酐酐酶酶(carbonic anhydrase)，使使H+以以纠纠正正酸酸中中毒毒，会会使使H+-Na-Na+交交换换 ，K+-NaNa+交交换换 ，造造成成血血K+。（临床上应予注意）（临床上应予注意）现在学习的是第33页，共48页2.NH3的分泌的分泌远远球球小小管管和和集集合合管管的的上上皮皮细细胞胞在在代代谢谢过过程程中中产产生生NH3 The epithelial cells of the distal tubule and collecting duct produce NH3 during the process of metabolism.谷
32、氨酰胺谷氨酰胺（Glutamyl)(脱氢）脱氢）NH3 扩散到小管液扩散到小管液 NH3+H+NH4+现在学习的是第34页，共48页3K+的分泌的分泌来源：尿来源：尿K+来自远曲小管和集合管的分泌，原尿中的来自远曲小管和集合管的分泌，原尿中的K+在近球小管已被重吸收入血。在近球小管已被重吸收入血。The potassium ions in urine is secreted by distal tubule and collecting duct,and the potassium ions in ultrafiltrate is reabsorbed into blood in proxim
33、al tubule.特点：特点：A.K+的分泌是一种被动分泌过程，与的分泌是一种被动分泌过程，与Na+-K+交换交换B.有关。有关。B.Na+主动重吸收，造成管腔内主动重吸收，造成管腔内-10-45mV，促使促使K+从组织液扩散入管腔内液。从组织液扩散入管腔内液。现在学习的是第35页，共48页4.其它物质排泄：其它物质排泄：肌肌 酐酐（creatinine）、对对 氨氨 基基 马马 尿尿 酸酸（aminohippurate）既滤过又排泄既滤过又排泄青青 霉霉 素素(benzylpenicillin）、酚酚 红红(phenolsulfonphthalein）主要是排泄主要是排泄现在学习的是第36
34、页，共48页5.影响肾小管与集合管泌尿机能的因素影响肾小管与集合管泌尿机能的因素(1)小小管管液液中中溶溶质质的的浓浓度度(the concentration of solute in tubule)溶质浓度溶质浓度 ，渗透压，渗透压 ，重吸收，重吸收 。渗渗透透性性利利尿尿(osmotic diuresis)提提高高小小管管液液溶溶质质浓度，达到利尿浓度，达到利尿(2)肾小球滤过率肾小球滤过率(glomerular filtration rate)现在学习的是第37页，共48页球管平衡球管平衡(glomerulotubular balance)：在在近近球球小小管管中中：GFR ，重重吸吸收
35、收率率 ；反之亦然反之亦然 即即不不管管GFR升升高高或或降降低低，滤滤液液的的重重吸吸收收率率始始终终占占GFR的的6570%左左右右（重重吸吸收收率为率为6570%）One of the most basic mechanisms for controlling tubular reabsorption is the intrinsic ability of the tubules to increase their reabsorption rate in response to increased tubular load.This phenomenon is referred to
36、as glomerulotubular balance.If GFR is increased,the absolute rate of proximal tubular reabsorption also increases,and the percentage of GFR reabsorbed in the proximal tubular remains relatively constant at about 65-70 percent.现在学习的是第38页，共48页机制：机制：a.近近球球小小管管对对Na+的的定定比比重重吸吸收收，对对Na+重重吸吸收收量量是是滤滤过过量的量的65
37、70%.The percentage of GFR reabsorbed in the proximal tubular remains relatively constant at about 65-70 percent.b.肾小管重吸收机能对肾小管重吸收机能对GFR的影响。的影响。重吸收重吸收 小管内压小管内压 囊内压囊内压 有效滤过压有效滤过压 滤过滤过 球球管管平平衡衡在在渗渗透透性性利利尿尿(osmotic diuresis)时时会会被被打打乱乱，6570%水肿水肿现在学习的是第39页，共48页第四节第四节 尿液的浓缩和稀释尿液的浓缩和稀释 concentration and dil
38、ution of urine 肾肾脏脏对对尿尿液液的的浓浓缩缩和和稀稀释释能能力力在在调调节节水水平平衡衡方方面面有有极极为为重要的作用。重要的作用。一一、尿尿浓浓缩缩和和稀稀释释的的机机制制逆流学说逆流学说（一）逆流倍增与逆流交换（一）逆流倍增与逆流交换髓髓袢袢、集集合合管管结结构构排排列列相相似似于逆流倍增的模型于逆流倍增的模型直直小小血血管管的的结结构构排排列列近近似似于于逆逆流交换模型。流交换模型。现在学习的是第40页，共48页（二）逆流学说（二）逆流学说用用冰冰点点降降低低法法测测定定肾肾分分层层切切片片的的渗渗透透压压，发发现现：皮皮质质部部组组织织液液体体与与血血浆浆是是等等渗渗
39、的的，髓髓质质部部随随髓髓质质外外层层向向乳乳头头部部深深入入而而逐逐渐渐升升高高，即即渗渗透透压压由由外外向向内内逐逐步步升升高高，有有明明确梯度。确梯度。现在学习的是第41页，共48页现在学习的是第42页，共48页1.髓质渗透压梯度形成机制髓质渗透压梯度形成机制the major factors that contribute to the buildup of solutes concentration into the renal medulla are as follows:A.外外髓髓部部渗渗透透压压梯梯度度主主要要是是由由髓髓袢袢升升支支粗粗段段NaCl的的重重吸吸收收形形成成的
40、的（Na+主主动动重重吸吸收收，Cl-继继发发性性主主动动重重吸收）吸收）The main force is active transport of sodium ions and co-transport of potassium,chloride,and other ions out of the thick portion of the ascending limb of the loop of Henle into the medullary interstitium.B.内内髓髓部部组组织织间间液液的的渗渗透透压压是是由由内内髓髓部部集集合合管管扩扩散散出出来来的的尿尿素素以以及及升
41、升支支细细段段扩扩散散出出来来的的NaCl这这两两个个因素形成因素形成.Passive diffusion of large amounts of urea from the inner medullary collecting ducts into the medullary interstitium and NaCl from thin segment of ascending limb.现在学习的是第43页，共48页C.髓髓袢袢升升支支粗粗段段对对Na+和和Cl-的的主主动动重重吸吸收收是是主主要要动动力力，尿尿素素再再循循环环则则促促成成了了整整个个髓质渗透压梯度的建立。髓质渗透压梯度
42、的建立。The main force is the active transport of sodium ions and chloride ions in thick portion of the ascending limb of the loop of Henle,and urea recirculation also contributes to the whole hyperosmotic renal medullary interstitium.现在学习的是第44页，共48页1.髓质渗透压梯度形成机制髓质渗透压梯度形成机制D.远曲小管及皮质部和外髓部的集合管对尿素不易通透,水被重吸
43、收,小管液中尿素的浓度逐渐升高。In distal tubule and collecting duct,there is little permeability to urea,and water is reabsorbed,so that the concentration of urea rises gradually.E.髓袢降支细段对尿素及Na+都不易通透,对水易通透,水被“抽吸”出来,小管液被浓缩，其中尿素及Na+的浓度不断升高。Becasuse there is a high permeability to water and little permeability to ure
44、a and sodium ions in thin segment of descending limb,water is suctioned by osmosis and the tubular fluid reaches equilibrium with the surrounding interstitial fluid of the renal medulla,which is very hypertonic.*形成机制简图*现在学习的是第45页，共48页（三）尿液的浓缩与稀释（三）尿液的浓缩与稀释1.尿尿液液浓浓缩缩：机机体体缺缺水水血血浆浆晶晶体体渗渗透透压压 ADH 集集合合管管
45、对对水水通通透透性性 ，管管外外为为高高渗渗环环境境，管管内内水水份份被被吸吸到到管管外外小管液浓缩小管液浓缩When body is in lack of water,the crystal osmotic pressure increases,and this promotes the release of ADH,thus,the permeability to water in collecting duct increases,the water in tubule is reabsorbed into the interstitial,so it forms a concentra
46、ted urine.现在学习的是第46页，共48页2.尿液稀释：机体水过剩尿液稀释：机体水过剩血浆晶体渗透压血浆晶体渗透压 ADH 集集合合管管对对水水不不通通透透。因因而而不不受受髓髓质质高高渗渗压压影影响响，加加上上流流经经远远曲曲小小管管的的Na+继继续续被被主主动动重重吸吸收收，水水却却难难于于吸收，小管液渗透压吸收，小管液渗透压 形成低渗尿排出。形成低渗尿排出。When there is a large excess of water in the body,the crystal osmotic pressure will decrease,and this reduces the release of ADH,so the collecting duct is impermeable to water,and the sodium ion is reabsorbed in distal tubule,all these lead to the tubular osmosis pressure decreasing and forming a dilute urine.现在学习的是第47页，共48页感感谢谢大大家家观观看看现在学习的是第48页，共48页