腎小管與集合管的重吸收

1、第二節(jié) 腎小管與集合管的重吸收 Reabsorption in the renal tubule and collecting duct,超濾液量(ultrafiltrate volume)180L /日 尿量(urine volume)1.5L /日 提示99%被重吸收 1%排出體外 某物質(zhì) 終尿濃度u / 血漿濃度P 反映物質(zhì)被重吸收或分泌的情況 因為水的重吸收量達(dá)99%，流量縮小了100倍， 所以u/p=100的物質(zhì)既不被重吸收又不被分泌和排泄 u/p100如肌酐(creatinine)等，提示腎小管還有分泌和排泄功能,重吸收部位,近球小管(proximal tubule) 14mm,刷

2、狀緣(brush border)增大重吸收面積 髓袢(Henles loop) 210mm 遠(yuǎn)球小管(distal tubule) 13.6mm 集合管(collecting duct) 20mm,一、重吸收的方式,1.被動重吸收(passive transport)：指小管液中的水和溶質(zhì)依借電化學(xué)差通過腎小管上皮細(xì)胞進(jìn)入細(xì)胞外液的過程。 Water and solutes are transported across the tubular epithelial cells into the extracellular fluid that is mediated by electronic

3、 and chemical forces. 水借滲透壓(osmotic forces)之差被動重吸收，滲透壓差是其動力。 溶質(zhì)濃度差(difference of concentration)和電位差(difference of potential)（電化學(xué)差）是其被動重吸收的動力,濃度差,電位差,Na,Na,主動,Na,Na,H,2,O,Cl,Cl,_,尿素,尿素被動擴(kuò)散,2.主動重吸收(active transport)：指腎小管上皮細(xì)胞逆電化學(xué)差，將小管內(nèi)溶質(zhì)主動轉(zhuǎn)運到小管外組織間液的過程。 Active transport can move a solute against an ele

4、ctrochemical gradient and requires energy derived from metabolism. 逆濃度差 逆電位差,髓袢升支粗段(thick segment of ascending limb) 繼發(fā)性主動轉(zhuǎn)運(secondary active transport) 特點：逆電化學(xué)差 耗能 Characteristics: against an electrochemical gradient and requires energy ) 葡萄糖(glucose)、氨基酸(amino acid)、Na+等主動重吸收,二、幾種物質(zhì)的重吸收1. Na+的重吸收,

5、方式主動重吸收(active transport) 原尿(glomerular filtrate) Na+ 500g /日， 終尿(urine) Na+ 35g /日 99%回收 地點和吸收比例： 近球小管：占濾過量6570% 遠(yuǎn)曲小管：10% 髓袢：20% 集合管：耗O2 1克，重吸收Na+ 2030克主動轉(zhuǎn)運,各段小管重吸收Na+ 的機(jī)制 近球小管 Proximal tubule 近球小管前半段： Na+與GS、氨基酸同向轉(zhuǎn)運(symport) 主動重吸收(active transport) Na +與H + 逆向轉(zhuǎn)運(antiport,近球小管后半段： Na+、Cl- 細(xì)胞旁路被動重吸收

6、(paracellular pathway,近球小管泵漏模式(pump-leak model,A 首先小管腔Na+順濃度差擴(kuò)散入小管細(xì)胞內(nèi) There is a concentration gradient favoring sodium diffusion into the cell. B 細(xì)胞側(cè)膜的鈉泵將其泵入細(xì)胞間隙 The cell has sodium pump to transport sodium out of the cell into the interstitium. C 水因滲透壓被吸引到間隙，造成間隙內(nèi)靜水壓升高 Water moves to the interstit

7、ium by osmosis,and it leads to a high level of hydrostatic pressure in interstitium,D 靜水壓升高引起Na+和水通過基膜進(jìn)入細(xì)胞間液和相鄰毛細(xì)血管，并有回漏現(xiàn)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

8、 to tubule. E 在Na+被重吸收時，尚有相當(dāng)量的負(fù)離子（HCO3- 或Cl-）順Na+被重吸收時造成的電位差而被重吸收。 Many negative ions are reabsorbed by difference of potential induced by the process of sodium reabsorption,遠(yuǎn)曲小管：Na+重吸收量少 A 緊密連接(tight junctions)對Na+通透性低，回漏量少 B 管內(nèi)外濃度差大，電位差大 20mfT/L : 140mfT/L 管內(nèi)-1045 mV C 管腔膜(luminal membrane)和管周膜(ba

9、solateral membrane)分布有Na+泵(sodium pump)，可將Na+泵到細(xì)胞外液和毛細(xì)血管內(nèi) D 伴有負(fù)離子重吸收和Na+ -H+ 、Na+-K+交換,髓袢(Henles loop)：主動轉(zhuǎn)運與Cl-繼發(fā)性主動轉(zhuǎn)運(secondary active transport)升支粗段被動轉(zhuǎn)運相結(jié)合。 集合管(connecting tubule)：主動轉(zhuǎn)運，Na+重吸收造成管內(nèi)-35mV。機(jī)制未明,2. Cl-的重吸收,大部分是伴隨Na+的主動重吸收而被動重吸收。 When sodium is reabsorbed through the tubular epithelial c

10、ell,negative ions such as chloride are transported passively along with sodium. 各段小管重吸收Cl-的機(jī)制： 近球小管(proximal tubule)：管內(nèi)負(fù)電位是Na+依賴性,A Na+的主動重吸收形成小管內(nèi)外電位差，管內(nèi)-4mV Sodium is positively reabsorbed from the tubule. This creates a difference of potential. B 負(fù)離子HCO3-、Cl-順電位差被動重吸收 Negative ions such as HCO3-、C

11、l- are passively reabsorbed by difference of potential. C HCO3-比Cl-優(yōu)先重吸收，加上滲透壓差導(dǎo)致水的重吸收 小管液中Cl-濃度 Preferential reabsorption of HCO3- and the reabsorption of water by osmosis pressure lead to a high concentration of chloride in tubule. D Cl-的管內(nèi)外濃度差又造成Cl-被動重吸收 Cl- is reabsorbed passively by the differe

12、nce of concentration,髓袢升支粗段，管腔內(nèi)正電位（+2+10mV,正電位依賴Cl-、K+存在。 Na+、Cl-、K+由同一載體協(xié)同轉(zhuǎn)運。 Movement of sodium across the luminal membrane is mediated primarily by a 1-sodium,2-chloride,1-potassium cotransporter. 用哇巴因(-) 鈉泵，轉(zhuǎn)運受阻，提示Na+泵參與此過程，機(jī)制可能如下： The transport is blocked by using ouabain which blocks the activ

13、ity of sodium pump,A 升支粗段上皮細(xì)胞管周膜的Na+泵將Na+由胞內(nèi)泵向組織間液 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，細(xì)胞內(nèi)Na+ ，出現(xiàn)管腔內(nèi)與細(xì)胞內(nèi)Na+濃度差 Sodium pump maintains a low intracellular sodium concentration,C 管腔

14、內(nèi)Na+順此濃度差擴(kuò)散到細(xì)胞內(nèi)，但須與Cl-、K+由同一載體協(xié)同轉(zhuǎn)運。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,

15、1-potassium cotransporter,D 進(jìn)入細(xì)胞后， Na+經(jīng)Na+泵泵到組織間液 Na+ is transported to interstitial fluid by sodium pump. Cl-順濃度差經(jīng)管周膜擴(kuò)散到組織間液 Cl- diffuses into interstitial fluid through basolateral membrane. K+由于濃度差經(jīng)管腔膜返回管腔內(nèi) K+ returns to tubule through basolateral membrane by difference of concentration,E 由于Cl-進(jìn)入

16、組織間液多，K+返回管腔內(nèi)液多，造成管腔內(nèi)正電位 特點：Na+主動轉(zhuǎn)運(active transport)，Cl-繼發(fā)性主動轉(zhuǎn)運(secondary active transport)速尿(furosedon)、利尿酸(-)(crinuryl,3.水的重吸收,99%重吸收，1%排出體外 水的重吸收： 在近球小管重吸收，伴溶質(zhì)而重吸收，與體內(nèi)是否缺水無關(guān) In proximal tubule,the reabsorption of water is accompanied with the reabsorption of solutes. 在遠(yuǎn)曲小管和集合管吸收，吸收量受調(diào)節(jié)，體內(nèi)缺少水時重吸收

17、多，體內(nèi)不缺水時重吸收少。 In distal tubule and collecting duct water reabsorption is regulated by the condition of body,近球小管6570% 水在各段小管 髓袢 10% 重吸收比例 遠(yuǎn)曲小管 10% 集合管 1020% 近球小管管壁對水通透性高，高遠(yuǎn)曲小管34倍，是一種等滲重吸收。 In proximal tubule， the process of water reabsorption is isosmotic because the permeability of tubule to water

18、is high. 髓袢、遠(yuǎn)曲小管集合管對水的重吸收機(jī)制，見尿液濃縮與稀釋,4. HCO3-的重吸收,特點：腎小管重吸收HCO3-是以CO2的形式而非直接以HCO3-的形式進(jìn)行，回到血中的HCO3-是由細(xì)胞產(chǎn)生，并非小管液中的HCO3-。 HCO3- is reabsorbed as a gas form. HCO3-比Cl-優(yōu)先重吸收，是因為CO2能迅速透過管腔膜,5.K+的重吸收,濾過液35克/日，終尿24克/日 主細(xì)胞重吸收Na+和水, 分泌K+ 。閏細(xì)胞則主要分泌H+。 The principal cells reabsorb sodium and water and secrete p

19、otassium; the intercalated cells secrete hydrogen. 特點：濾過液中的K+絕大部分被重吸收（在近球小管），終尿中的K+主要是由遠(yuǎn)曲小管和集合管分泌。 Almost all potassium in proximal tubule is reabsorbed,and the potassium in urine is mostly secreted by distal tubule and collecting duct. 近球小管管腔內(nèi)-4mV，K+重吸收逆電位差主動重吸收,6.葡萄糖的重吸收,A 逆濃度差主動重吸收 B 借助Na+的主動重吸收而

20、繼發(fā)主動重吸收 C 與刷狀緣載體蛋白有關(guān)，協(xié)同轉(zhuǎn)運 D 胞內(nèi)葡萄糖通過管周膜進(jìn)入組織間液的過程是易化擴(kuò)散。 A specific carrier protein 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,g

21、lucose exits across the basolateral membranes by facilitated diffusion,driven by the high glucose concentration in the cell,腎糖閾(renal glucose threshold)：當(dāng)血中葡萄糖濃度160180mg%時，超過部分腎小管重吸收葡萄糖的能力，出現(xiàn)尿糖。 When the concentration of glucose in blood is above 160180mg%,a small amount of glucose begins to appear

22、in the urine. 葡萄糖吸收極限量(transport maximum)：當(dāng)血糖濃度增高到令全部腎小管對糖重吸收的能力到達(dá)極限時，此值叫。（男375mg/min，女300mg/min） The overall transport maximum for the kidneys is reached when all nephrons have reached their maximal capacity to reabsorb glucose. E 如近球小管對Na+重吸收 ，葡萄糖吸收極限量也,7.其它物質(zhì)重吸收,氨基酸同葡萄糖 HPO4 、SO4與Na+伴聯(lián),第三節(jié) 腎小管與集合

23、管的分泌和排泄,腎小管分泌(tubular secretion)：指小管上皮細(xì)胞通過新陳代謝，將它所產(chǎn)生的物質(zhì)分泌到小管液中去的過程。 腎小管排泄(tubular excretion) ：指腎小管上皮細(xì)胞將血液中某些物質(zhì)直接排到小管中去的過程,1.H+的分泌,H+的產(chǎn)生： CO2+H2O H2CO3 HCO3 - +H+ H+-Na+交換，方向相反, 叫逆向交換(counter-transport) H+分泌到小管液中，主要在近球小管發(fā)生,遠(yuǎn)曲小管和集合管：除H+ -Na+交換外，還有K+-Na+交換，兩者相互抑制，當(dāng)酸中毒時H+ ，H+-Na+交換加強(qiáng)，K+-Na+交換 ，或造成血K+ ，反

24、過來用乙酰唑胺(-) 碳酸酐酶(carbonic anhydrase)，使H+ 以糾正酸中毒，會使H+-Na+交換 ，K+- Na+交換 ，造成血K+ 。 （臨床上應(yīng)予注意,2.NH3的分泌,遠(yuǎn)球小管和集合管的上皮細(xì)胞在代謝過程中產(chǎn)生NH3 The epithelial cells of the distal tubule and collecting duct produce NH3 during the process of metabolism. 谷氨酰胺（Glutamyl)(脫氫） NH3 擴(kuò)散到小管液 NH3+H+ NH4,3K+的分泌,來源：尿K+來自遠(yuǎn)曲小管和集合管的分泌，原尿中

25、的K+ 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 proximal tubule. 特點： K+的分泌是一種被動分泌過程，與Na+- K+交換 有關(guān)。 B. Na+主動重吸收，造成管腔內(nèi)-10-45mV，促使K+ 從組織液擴(kuò)散入管腔內(nèi)液,4.其它物質(zhì)排泄,肌酐（creatinine）、對氨基馬尿酸（aminohippura

26、te）既濾過又排泄 青霉素(benzylpenicillin）、酚紅(phenolsulfonphthalein）主要是排泄,5.影響腎小管與集合管泌尿機(jī)能的因素,1)小管液中溶質(zhì)的濃度(the concentration of solute in tubule) 溶質(zhì)濃度 ，滲透壓 ，重吸收 。 滲透性利尿(osmotic diuresis)提高小管液溶質(zhì)濃度，達(dá)到利尿 (2)腎小球濾過率(glomerular filtration rate,球管平衡(glomerulotubular balance)： 在近球小管中：GFR ，重吸收率 ；反之亦然 即不管GFR升高或降低，濾液的重吸收率始

27、終占GFR的6570%左右（重吸收率為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 as glomerulotubular balance.If GFR is increased,the absolut

28、e 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,機(jī)制： a.近球小管對Na+的定比重吸收，對Na+重吸收量是濾過量的6570%. The percentage of GFR reabsorbed in the proximal tubular remains relatively constant at abou

29、t 65-70 percent. b.腎小管重吸收機(jī)能對GFR的影響。 重吸收 小管內(nèi)壓 囊內(nèi)壓 有效濾過壓 濾過 球管平衡在滲透性利尿(osmotic diuresis)時會被打亂，6570%水腫,第四節(jié) 尿液的濃縮和稀釋 concentration and dilution of urine,腎臟對尿液的濃縮和稀釋能力在調(diào)節(jié)水平衡方面有極為重要的作用。 一、尿濃縮和稀釋的機(jī)制逆流學(xué)說 （一）逆流倍增與逆流交換 髓袢、集合管結(jié)構(gòu)排列相似于逆流倍增的模型 直小血管的結(jié)構(gòu)排列近似于逆流交換模型,二）逆流學(xué)說 用冰點降低法測定腎分層切片的滲透壓，發(fā)現(xiàn)：皮質(zhì)部組織液體與血漿是等滲的，髓質(zhì)部隨髓質(zhì)外層

30、向乳頭部深入而逐漸升高，即滲透壓由外向內(nèi)逐步升高，有明確梯度,1.髓質(zhì)滲透壓梯度形成機(jī)制the major factors that contribute to the buildup of solutes concentration into the renal medulla are as follows,A.外髓部滲透壓梯度主要是由髓袢升支粗段NaCl的重吸收形成的（Na+主動重吸收，Cl-繼發(fā)性主動重吸收） The main force is active transport of sodium ions and co-transport of potassium,chloride,a

31、nd other ions out of the thick portion of the ascending limb of the loop of Henle into the medullary interstitium. B.內(nèi)髓部組織間液的滲透壓是由內(nèi)髓部集合管擴(kuò)散出來的尿素以及升支細(xì)段擴(kuò)散出來的NaCl這兩個因素形成. Passive diffusion of large amounts of urea from the inner medullary collecting ducts into the medullary interstitium and NaCl from th

32、in segment of ascending limb,C.髓袢升支粗段對Na+和Cl-的主動重吸收是主要動力，尿素再循環(huán)則促成了整個髓質(zhì)滲透壓梯度的建立。 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 inter

33、stitium,1.髓質(zhì)滲透壓梯度形成機(jī)制,D. 遠(yuǎn)曲小管及皮質(zhì)部和外髓部的集合管對尿素不易通透, 水被重吸收, 小管液中尿素的濃度逐漸升高。 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. 髓袢降支細(xì)段對尿素及Na+都不易通透, 對水易通透, 水被“抽吸”出來, 小管液被濃縮，其中尿素及Na+的濃度不斷升高。 Becasuse there is a high permeability to water and l