医学英语教程-生物医学
Unit 6 Reading A
The Kidney and Its Working Unit
肾及其工作单位
For many diners, eating tender, pale green shoots of asparagus is a pleasurable springtime event, but the gastronomic experience has a peculiar sequel：The next time they urinate ,even if just 20 minutes after eating, they notice the characteristic scent of asparagus. A chemical in the food crosses the gut ,enters the bloodstream, is filtered out by the kidneys, and appears in the urine with amazing speed. Actually, the chemical is acted on no faster than any other compound. The kidneys are simply marvels at processing body fluids and filtering out the urea; the sodium ,potassium ,or chloride ions ;and the glucose, water ,and other materials that need to be excreted. The key to a kidney's rapid functioning lies in its complicated internal structure and in the effcient plumbing system of which it is a part.
对许多用餐者来说，吃到浅绿鲜嫩的芦笋是春季的一大享受，但享用完这种美食后会有一个奇特的后续：即使饭后仅20分钟,人们便会在上厕所时注意到尿液中有芦笋特殊的气味。芦笋中的某种化学物质以万分惊人的速度穿过肠子,进入循环的血液,并被肾脏过滤出来,最后出现在尿液中。事实上，这一化学物的作用并不比其他化合物更快些。起到加速体液循循环并过滤出尿素,钠、钾、氯离子、葡萄糖、水及一切需排泄的这些惊叹不已的作用的是肾脏。肾脏能快捷地发挥作用的关键就在于其复杂的内部结构，以及它作为其中一部分的高效率管道系统。
The Kidneys and Other Organs of the Excretory Systerm 肾脏和排泄系统的其他器官
It is sometimes stated that urination is our most compelling bodily function. You will probably agree if you have ever been hungry, tired ,cold ,and had a full bladder simultaneously and can recall the order in which you addressed those needs. This urgency has to do with the necessary waste removal role of the excretory system and with the system's particular anatomy.
人们有时说排尿是我们身体最急迫的功能。如果你曾经有过饥饿、疲倦、寒冷及膀胱满胀等感觉并能回忆起你处理这些身体需要的顺序，你就会同意以上那种说法。这种急迫感与排泄系统必要的排废作用和该系统特别的解剖结构有关。 The main organs of the excretory system are the two plump, dark red, crescent- shaped kidneys, each about the size of an adult's fist and located high in the abdominal cavity behind the stomach and the liver. For each kidney to carry out its vital blood-filtering activities ,it must receive a large, steady flow of blood.
排泄系统的主要器官是两个圆满的、暗红色的、月牙状的肾脏。每个约有成
人拳头大小, 位于腹腔上部胃、肝的后面。因为肾脏担负过滤血液的重要任务，所以必须接收到强大持续的血流。
This it does through the renal arteries, twin branches directly off the body's main
blood vessel, or aorta. Cleansed blood then leaves each kidney in large renal blood vein that drains into the body's largest vein. As the kidneys filter and remove excess water and waste substances from the blood, these materials collect as a concentrated urine in a central cavity in each kidney, then flow down a long tube called a ureter. The two ureters dump urine into a single storage sac, the urinary bladder, which in an adult can hold about 500 ml (a pint) of fluid. The bladder can distend to hold a bit more, but when it is full, it causes considerable pressure on nearby nerves and a feeling of urgency that can temporarily eclipse all other concerns. During urination ,the urine exits the body through the urethra ,the single tube that drains the bladder.
它穿过肾动脉，肾动脉即是直接离开人体主要血管或是主动脉的两条并行的血管。紧接着，干净的血液离开每一个肾后进入一管腔大的、可以排入静脉血至人体最大静脉的肾静脉。同时，两个肾过滤与清除血液中多余的水以及代谢废物，这些物质的收集后就成为在每一个肾的中央管内的浓缩后的尿液，接着这些尿液就沿着一条长长的管腔—输尿管向下流动。这两条输尿管把尿液倾倒入一个单个的用于储藏的囊腔内，这个囊腔便是成年人可以装得下500ml（一品脱）的液体的泌尿的膀胱。膀胱可以膨胀以至于多装一些尿液，但是当它饱满的时候，它可以对附近的神经造成相当大的压力以及急尿的感觉，这样可以暂时地使所有其他的问题消失。在排尿期间，尿通过尿道，从膀胱外导尿的一根导管排出体外。 The kidney has three distinct visible zones; an outer renal cortex zone: where initial blood filtering takes place; a central zone（renal medulla），divided into a number of fan-shaped pyramid regions that help conserve water and valuable solutes; and a hollow inner compartment（renal pelvis） ，where urine collects before it passes out of the kidney and down the ureter. The functional units of the kidney,twisted tubules called nephrons, reach from the outer cortex down into the central zone and drain into the hollow center.
肾脏有三个明显的可见的区域；一个是外层的肾皮质区域：最初血液过滤发生的位置；中心区（肾髓质），分成若干个扇形的金字塔区域，有助于保存水分和有价值的溶液；还有一个中空的内区域（肾盂），是尿液流出肾脏进入输尿管之前聚集的地方，在它从肾脏出来和沿着输尿管向下之前。肾脏的功能单位，扭曲的小管，称为肾单位，到达浅皮质区向下进入中央区并排入内部中空区。
Have you ever cleaned out a desk drawer - sorting,saving certain items for future use,discarding others,and then rechecking the drawer one last time ?If so, you have approximated the kidney's general sorting and cleansing action and its three basic processes - filtration,reabsorption,and secretion - all of which involve the nephron. 你有没有清理过抽屉——将物品分类、排序保存供以后使用,丢弃不需要的,最后复查抽屉里的物品? 如果是这样,你有近似肾的一般分类和清理行动的基本过程 , 过滤、重吸收和分泌——所有这些涉及肾元。
A human kidney contains roughly 1 million nephrons,each one a long, twisted,looping tubule. The tubule has one end that is enlarged and cup-shaped like a punched bas
ketball and that lies in close contact with blood capillaries;the other end drains away urine. If all the nephrons in an adult's kidney were straightened out and placed end to end, they would from a microscopically slender tube about 80km（50miles） long.
人类肾脏包含大约100万肾元,每一个小管长期扭曲,构成环形。小管一端,开杯形放大,像打篮球,位于密切接触血液毛细血管的地方;另一端排出尿液。如果所有的肾元在一个成年人的肾脏被拉直,从头拉到尾,它们在显微镜下显示长约80公里(50英里).
Nephrons are amazingly efficient at selectively removing wastes from the blood circulation while simultaneously conserving water,mineral ions, glucose,and other needed materials.In an adult human, 180 liters or more of blood - enough to fill a bathtub - pass through the 2 million nephrons in the two kidneys each day, we do not, of course,urinate 180liters a day or even the 6 or 7liters of fluid our bodieds contain,but instead the much more reasonable amount of about 1.5 liters per day. Clearly,the nephrons must accomplish a great deal of water recycling and conservation before they produce that smaller quantity of urine. Let us now take a close look at how a nephron works.
肾单位可以非常有效地选择性地把废物从血液循环,同时节约水,矿物离子、葡萄糖和其他必要的材料。成年人体内的180公升的血液——足以填满浴缸,每天通过这200万个肾元到两个肾，当然我们没有每天排180L的尿液，甚至是包含在我们体内6或7升的液体,而是更为合理的每天大约1.5升尿液.很明显,肾元必须完成大量的水回收和保存之前生产小数量的尿液。现在让我们来仔细看看肾元是如何工作的。
The nephron's specialized shape enables it to carry out three basic processes - filtration of small molecules from the blood, reabsorption of useful molecules from the urine back into the blood, and secretion of ions and some drugs from the blood into the urine.
肾单位的特殊形状使其执行三个基本过程——过滤血液中的小分子,再吸收有用的分子从回血液、尿液和离子的分泌和一些药物从血液进入尿液.
Filtration
过滤
The portion of the nephron that filters water and solutes from the blood is the enlarged, cuplike Bowman’S capsule in the kidney’s outer cortex. Each Bowman’S capsule surrounds a tight bundle of capillaries called a glomerulus, much the way the fingers of your right hand can wrap around your left fist. This enclosing capsule of kidney tissue surrounding a tuft of blood capillaries forms the closest contact between the excretory and circulatory systems. A finely meshed filter lies between the blood and the cavity of the Bowman’s capsule like a submicroscopic colander. As blood moves along through the capillaries, blood pressure forces the yellowish
fluid portion of blood out of the capillaries, through the pores of this delicate filter, and into the Bowman’S capsule, just as water pressure forces coffee through a coffee filter. The fineness of the pores is ultimately responsible for the nephron’s blood filtration activities:The Bowman’S capsule filter allows wastes, water and other small molecules to seep through its minute openings, while the crucial components of blood—red cell, antibodies, and other large proteins—remain behind in the capillaries. The passage of water, of sodium, potassium, and chloride ions, and of sugars, amino acids, nd urea out of the capillaries and into the lumen of the Bowman’S capsule passive and does not require any special output of energy other than blood pressure. The fluid, or filtrate, in the capsule in still very much like blood plasma, except that it conrtains no large proteins or cell.
肾过滤水的部分和从血液中分离的溶质是扩大的，杯状鲍曼氏囊在肾皮质的外面，每个鲍曼氏囊包裹的毛细血管成为肾小球，就像你右手的手指包绕你左手的拳头。这个封闭的胶囊肾组织周围的一簇毛细血管形成的排泄和循环系统之间亲密接触，处于血液和肾小囊腔之间的细网状过滤器就像一个亚滤器。随着血液移动通过毛细血管，血压促使一部分血液通过这个精细过滤器的微孔出毛细血管，并且进入鲍曼氏囊，就像水压促使咖啡通过咖啡过滤器。毛孔的细度基本上是负责肾单位血液的过滤活动：鲍曼氏囊过滤器允许废物，水和其他小分子通过它的小口处渗出，然而血液的关键成分—红细胞，抗体和其它的大分子蛋白质遗留在毛细血管的后面。水，钠，钾和氯离子，和糖类，氨基酸，尿素从毛细血管进入肾小囊腔的通道是被动的，除了血压不需要其他能量的输出。除了没有包含大分子蛋白质和细胞，在毛细血管中的流体或者滤出液仍然非常像血浆。
As if leaves the Bowman’s capsule, the filtrate enters the part of the nephron’s twisted tubule nearest the capsule,known as proximal (near) tubule.There,reabsorption begins and returns to the circulation most of the water ,the sodium and chloride ions ,the sugars,and the amino acids that were just filtered out of the blood in the Bowman’s capsule.
当滤出物离开肾小囊，进入肾单位中最接近肾小囊部分的弯曲小管,被称为近曲小管。在这里，重吸收启动，并将从鲍曼氏囊滤出的血液里的大部分水，钠，氯 离子，糖和氨基酸送回循环系统。
These materials move out through the walls of the proximal tubule and pass back into the blood via the surrounding capillaries.Instead of being driven passively by blood pressure,reabsorption of solutes in the proximal tubule depends on energy-costly active transport across cell membranes.As the ions are being reabsorbed in this way, 80 to 85 percent of the water in the original filtrate follows them passively back into the capillaries via the process of osmosis.
这些物质通过毛细血管壁搬运出去，并且经由周围的毛细血管回到血液中去。近曲小管的溶质重吸收不是 通过血压来被动运输，而是依靠消耗能量的主
动运输来穿透细胞膜。在离子以这种方式被重新吸收时，原滤出液中80%-85%的水通过渗透过程又随之被动地返回毛细血管。
Next,the filtrate passes down the descending arm of the nephron’s U-shaped loop of Henle’s,which is bathed by an increasingly salty fluid. Water leaves the loop of Henle’s by osmosis and reenters the blood of the capillaries surrounding the tubule.The filtrate then rounds the bend in the loop of Henle’s and moves up the ascending arm and through the distal tubule ( far from the Bowman’s capsule) toward the collecting duct.
然后，滤出物通过肾单位里的U型 亨利袢降支，这个部位不断受到 盐分越来越多的液体的冲洗。水通过渗透作用离开亨利袢支，再输入小管周围的毛细血管中的血液。滤液绕行亨利袢支的弯曲部分，沿着升支向上移动，并通过远端小管（远离肾小囊 ），接近集合管。
The walls of the distal tubule are not permeable to water ,but those of the collecting duct are;and even though the filtrate passing through the duct is already quite concentrated, the surrounding tissues are even saltier.Thus, more water diffuses out of the collecting duct by osmosis and enters the blood of the surrounding capillaries.
水不能通过远曲小管的 管壁，但收集管的管壁允许水通过；虽然通过收集管的滤过液浓度已经很高，但周围组织含盐量更大。因此，更多的水通过渗透作用在集合管中扩散开，并且进入周围毛细血管中的血液。
By the time the filtrate now called urine has reached the part of the collecting tubule in the innermost (and saltiest) region of the kidney’s medulla,99 percent of the water originally filtered from the blood in the Bowman’s capsule has been reabsorbed and returned to the body’s circulation.
等到过滤物（现在称为尿）到达肾脏髓质最深处（含盐）区域的收集小管部分时，99%从肾小囊的血液中最先滤过的水被重吸收回到身体循环。
Tubular Secretion
肾小管分泌
While the filtration and reabsorption activities of the kidneys’2million nephrons are removing salt and urea from the biood and forming urine, another process-tubular secretion-goes on simultaneously in both the proximal and distal tubules. Secretion removes a number of unwanted materials-including hydrogen ions, potassium ions, environmental pollutants like pesticides, and drug such as penicillin and Phenobarbital-from the blood in the capillaries surrounding the nephron and secretes them into the froming urine.
当肾脏中2百万肾单元的过滤与重吸收活动把盐和尿素从血液中移除，形成原尿时，另一个过程-管子的分泌，同时在近端小管和远端小管发生，分泌过程移除许多有害物质，包括氢离子，氯离子，环境污染物像杀虫剂，来自包绕肾单元和分泌形成原尿的毛细血管的血液中的青霉素，笨巴比妥等药品。
Tubular secretion is the physiological process that make drug testing possible-checking a person’s urine to see if he or she has taken drugs. Drug testing employs various laboratory techniques to detect even minute traces of the metabolic breakdown products of marijuana, cocaine, and many kinds of prescription drugs.
动运输来穿透细胞膜。在离子以这种方式被重新吸收时，原滤出液中80%-85%的水通过渗透过程又随之被动地返回毛细血管。
Next,the filtrate passes down the descending arm of the nephron’s U-shaped loop of Henle’s,which is bathed by an increasingly salty fluid. Water leaves the loop of Henle’s by osmosis and reenters the blood of the capillaries surrounding the tubule.The filtrate then rounds the bend in the loop of Henle’s and moves up the ascending arm and through the distal tubule ( far from the Bowman’s capsule) toward the collecting duct.
然后，滤出物通过肾单位里的U型 亨利袢降支，这个部位不断受到 盐分越来越多的液体的冲洗。水通过渗透作用离开亨利袢支，再输入小管周围的毛细血管中的血液。滤液绕行亨利袢支的弯曲部分，沿着升支向上移动，并通过远端小管（远离肾小囊 ），接近集合管。
The walls of the distal tubule are not permeable to water ,but those of the collecting duct are;and even though the filtrate passing through the duct is already quite concentrated, the surrounding tissues are even saltier.Thus, more water diffuses out of the collecting duct by osmosis and enters the blood of the surrounding capillaries.
水不能通过远曲小管的 管壁，但收集管的管壁允许水通过；虽然通过收集管的滤过液浓度已经很高，但周围组织含盐量更大。因此，更多的水通过渗透作用在集合管中扩散开，并且进入周围毛细血管中的血液。
By the time the filtrate now called urine has reached the part of the collecting tubule in the innermost (and saltiest) region of the kidney’s medulla,99 percent of the water originally filtered from the blood in the Bowman’s capsule has been reabsorbed and returned to the body’s circulation.
等到过滤物（现在称为尿）到达肾脏髓质最深处（含盐）区域的收集小管部分时，99%从肾小囊的血液中最先滤过的水被重吸收回到身体循环。
Tubular Secretion
肾小管分泌
While the filtration and reabsorption activities of the kidneys’2million nephrons are removing salt and urea from the biood and forming urine, another process-tubular secretion-goes on simultaneously in both the proximal and distal tubules. Secretion removes a number of unwanted materials-including hydrogen ions, potassium ions, environmental pollutants like pesticides, and drug such as penicillin and Phenobarbital-from the blood in the capillaries surrounding the nephron and secretes them into the froming urine.
当肾脏中2百万肾单元的过滤与重吸收活动把盐和尿素从血液中移除，形成原尿时，另一个过程-管子的分泌，同时在近端小管和远端小管发生，分泌过程移除许多有害物质，包括氢离子，氯离子，环境污染物像杀虫剂，来自包绕肾单元和分泌形成原尿的毛细血管的血液中的青霉素，笨巴比妥等药品。
Tubular secretion is the physiological process that make drug testing possible-checking a person’s urine to see if he or she has taken drugs. Drug testing employs various laboratory techniques to detect even minute traces of the metabolic breakdown products of marijuana, cocaine, and many kinds of prescription drugs.
管状分泌物是可能进行药物检测的生理过程-检查一个人的尿液，看他是否服药。药物检测使用各种实验室技术去察觉由新陈代谢故障产生的大麻，可卡因和许多指示药物的微小踪迹。
If a person takes a drug overdose and loses consciousness and no one is sure which drug was consumed, physicians quickly test the urine to identify the drug and determine the best treatment for saving the patient’s life. Two additional uses-testing athletes and employees for drug use in the playing field or on the job-are currently quite controversial.
如果一个人服药过多失去意识，没人确定他服用了哪种药物，内科医生讯速的检测尿去分辨药物从而决定最佳治疗方法去拯救病人的生命。两个额外的作用-检测运动员和员工在运动领域或工作中对药物的使用情况-在当前仍有争议。
医学英语教程-生物医学
Unit 6 Reading A
The Kidney and Its Working Unit
肾及其工作单位
For many diners, eating tender, pale green shoots of asparagus is a pleasurable springtime event, but the gastronomic experience has a peculiar sequel：The next time they urinate ,even if just 20 minutes after eating, they notice the characteristic scent of asparagus. A chemical in the food crosses the gut ,enters the bloodstream, is filtered out by the kidneys, and appears in the urine with amazing speed. Actually, the chemical is acted on no faster than any other compound. The kidneys are simply marvels at processing body fluids and filtering out the urea; the sodium ,potassium ,or chloride ions ;and the glucose, water ,and other materials that need to be excreted. The key to a kidney's rapid functioning lies in its complicated internal structure and in the effcient plumbing system of which it is a part.
对许多用餐者来说，吃到浅绿鲜嫩的芦笋是春季的一大享受，但享用完这种美食后会有一个奇特的后续：即使饭后仅20分钟,人们便会在上厕所时注意到尿液中有芦笋特殊的气味。芦笋中的某种化学物质以万分惊人的速度穿过肠子,进入循环的血液,并被肾脏过滤出来,最后出现在尿液中。事实上，这一化学物的作用并不比其他化合物更快些。起到加速体液循循环并过滤出尿素,钠、钾、氯离子、葡萄糖、水及一切需排泄的这些惊叹不已的作用的是肾脏。肾脏能快捷地发挥作用的关键就在于其复杂的内部结构，以及它作为其中一部分的高效率管道系统。
The Kidneys and Other Organs of the Excretory Systerm 肾脏和排泄系统的其他器官
It is sometimes stated that urination is our most compelling bodily function. You will probably agree if you have ever been hungry, tired ,cold ,and had a full bladder simultaneously and can recall the order in which you addressed those needs. This urgency has to do with the necessary waste removal role of the excretory system and with the system's particular anatomy.
人们有时说排尿是我们身体最急迫的功能。如果你曾经有过饥饿、疲倦、寒冷及膀胱满胀等感觉并能回忆起你处理这些身体需要的顺序，你就会同意以上那种说法。这种急迫感与排泄系统必要的排废作用和该系统特别的解剖结构有关。 The main organs of the excretory system are the two plump, dark red, crescent- shaped kidneys, each about the size of an adult's fist and located high in the abdominal cavity behind the stomach and the liver. For each kidney to carry out its vital blood-filtering activities ,it must receive a large, steady flow of blood.
排泄系统的主要器官是两个圆满的、暗红色的、月牙状的肾脏。每个约有成
人拳头大小, 位于腹腔上部胃、肝的后面。因为肾脏担负过滤血液的重要任务，所以必须接收到强大持续的血流。
This it does through the renal arteries, twin branches directly off the body's main
blood vessel, or aorta. Cleansed blood then leaves each kidney in large renal blood vein that drains into the body's largest vein. As the kidneys filter and remove excess water and waste substances from the blood, these materials collect as a concentrated urine in a central cavity in each kidney, then flow down a long tube called a ureter. The two ureters dump urine into a single storage sac, the urinary bladder, which in an adult can hold about 500 ml (a pint) of fluid. The bladder can distend to hold a bit more, but when it is full, it causes considerable pressure on nearby nerves and a feeling of urgency that can temporarily eclipse all other concerns. During urination ,the urine exits the body through the urethra ,the single tube that drains the bladder.
它穿过肾动脉，肾动脉即是直接离开人体主要血管或是主动脉的两条并行的血管。紧接着，干净的血液离开每一个肾后进入一管腔大的、可以排入静脉血至人体最大静脉的肾静脉。同时，两个肾过滤与清除血液中多余的水以及代谢废物，这些物质的收集后就成为在每一个肾的中央管内的浓缩后的尿液，接着这些尿液就沿着一条长长的管腔—输尿管向下流动。这两条输尿管把尿液倾倒入一个单个的用于储藏的囊腔内，这个囊腔便是成年人可以装得下500ml（一品脱）的液体的泌尿的膀胱。膀胱可以膨胀以至于多装一些尿液，但是当它饱满的时候，它可以对附近的神经造成相当大的压力以及急尿的感觉，这样可以暂时地使所有其他的问题消失。在排尿期间，尿通过尿道，从膀胱外导尿的一根导管排出体外。 The kidney has three distinct visible zones; an outer renal cortex zone: where initial blood filtering takes place; a central zone（renal medulla），divided into a number of fan-shaped pyramid regions that help conserve water and valuable solutes; and a hollow inner compartment（renal pelvis） ，where urine collects before it passes out of the kidney and down the ureter. The functional units of the kidney,twisted tubules called nephrons, reach from the outer cortex down into the central zone and drain into the hollow center.
肾脏有三个明显的可见的区域；一个是外层的肾皮质区域：最初血液过滤发生的位置；中心区（肾髓质），分成若干个扇形的金字塔区域，有助于保存水分和有价值的溶液；还有一个中空的内区域（肾盂），是尿液流出肾脏进入输尿管之前聚集的地方，在它从肾脏出来和沿着输尿管向下之前。肾脏的功能单位，扭曲的小管，称为肾单位，到达浅皮质区向下进入中央区并排入内部中空区。
Have you ever cleaned out a desk drawer - sorting,saving certain items for future use,discarding others,and then rechecking the drawer one last time ?If so, you have approximated the kidney's general sorting and cleansing action and its three basic processes - filtration,reabsorption,and secretion - all of which involve the nephron. 你有没有清理过抽屉——将物品分类、排序保存供以后使用,丢弃不需要的,最后复查抽屉里的物品? 如果是这样,你有近似肾的一般分类和清理行动的基本过程 , 过滤、重吸收和分泌——所有这些涉及肾元。
A human kidney contains roughly 1 million nephrons,each one a long, twisted,looping tubule. The tubule has one end that is enlarged and cup-shaped like a punched bas
ketball and that lies in close contact with blood capillaries;the other end drains away urine. If all the nephrons in an adult's kidney were straightened out and placed end to end, they would from a microscopically slender tube about 80km（50miles） long.
人类肾脏包含大约100万肾元,每一个小管长期扭曲,构成环形。小管一端,开杯形放大,像打篮球,位于密切接触血液毛细血管的地方;另一端排出尿液。如果所有的肾元在一个成年人的肾脏被拉直,从头拉到尾,它们在显微镜下显示长约80公里(50英里).
Nephrons are amazingly efficient at selectively removing wastes from the blood circulation while simultaneously conserving water,mineral ions, glucose,and other needed materials.In an adult human, 180 liters or more of blood - enough to fill a bathtub - pass through the 2 million nephrons in the two kidneys each day, we do not, of course,urinate 180liters a day or even the 6 or 7liters of fluid our bodieds contain,but instead the much more reasonable amount of about 1.5 liters per day. Clearly,the nephrons must accomplish a great deal of water recycling and conservation before they produce that smaller quantity of urine. Let us now take a close look at how a nephron works.
肾单位可以非常有效地选择性地把废物从血液循环,同时节约水,矿物离子、葡萄糖和其他必要的材料。成年人体内的180公升的血液——足以填满浴缸,每天通过这200万个肾元到两个肾，当然我们没有每天排180L的尿液，甚至是包含在我们体内6或7升的液体,而是更为合理的每天大约1.5升尿液.很明显,肾元必须完成大量的水回收和保存之前生产小数量的尿液。现在让我们来仔细看看肾元是如何工作的。
The nephron's specialized shape enables it to carry out three basic processes - filtration of small molecules from the blood, reabsorption of useful molecules from the urine back into the blood, and secretion of ions and some drugs from the blood into the urine.
肾单位的特殊形状使其执行三个基本过程——过滤血液中的小分子,再吸收有用的分子从回血液、尿液和离子的分泌和一些药物从血液进入尿液.
Filtration
过滤
The portion of the nephron that filters water and solutes from the blood is the enlarged, cuplike Bowman’S capsule in the kidney’s outer cortex. Each Bowman’S capsule surrounds a tight bundle of capillaries called a glomerulus, much the way the fingers of your right hand can wrap around your left fist. This enclosing capsule of kidney tissue surrounding a tuft of blood capillaries forms the closest contact between the excretory and circulatory systems. A finely meshed filter lies between the blood and the cavity of the Bowman’s capsule like a submicroscopic colander. As blood moves along through the capillaries, blood pressure forces the yellowish
fluid portion of blood out of the capillaries, through the pores of this delicate filter, and into the Bowman’S capsule, just as water pressure forces coffee through a coffee filter. The fineness of the pores is ultimately responsible for the nephron’s blood filtration activities:The Bowman’S capsule filter allows wastes, water and other small molecules to seep through its minute openings, while the crucial components of blood—red cell, antibodies, and other large proteins—remain behind in the capillaries. The passage of water, of sodium, potassium, and chloride ions, and of sugars, amino acids, nd urea out of the capillaries and into the lumen of the Bowman’S capsule passive and does not require any special output of energy other than blood pressure. The fluid, or filtrate, in the capsule in still very much like blood plasma, except that it conrtains no large proteins or cell.
肾过滤水的部分和从血液中分离的溶质是扩大的，杯状鲍曼氏囊在肾皮质的外面，每个鲍曼氏囊包裹的毛细血管成为肾小球，就像你右手的手指包绕你左手的拳头。这个封闭的胶囊肾组织周围的一簇毛细血管形成的排泄和循环系统之间亲密接触，处于血液和肾小囊腔之间的细网状过滤器就像一个亚滤器。随着血液移动通过毛细血管，血压促使一部分血液通过这个精细过滤器的微孔出毛细血管，并且进入鲍曼氏囊，就像水压促使咖啡通过咖啡过滤器。毛孔的细度基本上是负责肾单位血液的过滤活动：鲍曼氏囊过滤器允许废物，水和其他小分子通过它的小口处渗出，然而血液的关键成分—红细胞，抗体和其它的大分子蛋白质遗留在毛细血管的后面。水，钠，钾和氯离子，和糖类，氨基酸，尿素从毛细血管进入肾小囊腔的通道是被动的，除了血压不需要其他能量的输出。除了没有包含大分子蛋白质和细胞，在毛细血管中的流体或者滤出液仍然非常像血浆。
As if leaves the Bowman’s capsule, the filtrate enters the part of the nephron’s twisted tubule nearest the capsule,known as proximal (near) tubule.There,reabsorption begins and returns to the circulation most of the water ,the sodium and chloride ions ,the sugars,and the amino acids that were just filtered out of the blood in the Bowman’s capsule.
当滤出物离开肾小囊，进入肾单位中最接近肾小囊部分的弯曲小管,被称为近曲小管。在这里，重吸收启动，并将从鲍曼氏囊滤出的血液里的大部分水，钠，氯 离子，糖和氨基酸送回循环系统。
These materials move out through the walls of the proximal tubule and pass back into the blood via the surrounding capillaries.Instead of being driven passively by blood pressure,reabsorption of solutes in the proximal tubule depends on energy-costly active transport across cell membranes.As the ions are being reabsorbed in this way, 80 to 85 percent of the water in the original filtrate follows them passively back into the capillaries via the process of osmosis.
这些物质通过毛细血管壁搬运出去，并且经由周围的毛细血管回到血液中去。近曲小管的溶质重吸收不是 通过血压来被动运输，而是依靠消耗能量的主
动运输来穿透细胞膜。在离子以这种方式被重新吸收时，原滤出液中80%-85%的水通过渗透过程又随之被动地返回毛细血管。
Next,the filtrate passes down the descending arm of the nephron’s U-shaped loop of Henle’s,which is bathed by an increasingly salty fluid. Water leaves the loop of Henle’s by osmosis and reenters the blood of the capillaries surrounding the tubule.The filtrate then rounds the bend in the loop of Henle’s and moves up the ascending arm and through the distal tubule ( far from the Bowman’s capsule) toward the collecting duct.
然后，滤出物通过肾单位里的U型 亨利袢降支，这个部位不断受到 盐分越来越多的液体的冲洗。水通过渗透作用离开亨利袢支，再输入小管周围的毛细血管中的血液。滤液绕行亨利袢支的弯曲部分，沿着升支向上移动，并通过远端小管（远离肾小囊 ），接近集合管。
The walls of the distal tubule are not permeable to water ,but those of the collecting duct are;and even though the filtrate passing through the duct is already quite concentrated, the surrounding tissues are even saltier.Thus, more water diffuses out of the collecting duct by osmosis and enters the blood of the surrounding capillaries.
水不能通过远曲小管的 管壁，但收集管的管壁允许水通过；虽然通过收集管的滤过液浓度已经很高，但周围组织含盐量更大。因此，更多的水通过渗透作用在集合管中扩散开，并且进入周围毛细血管中的血液。
By the time the filtrate now called urine has reached the part of the collecting tubule in the innermost (and saltiest) region of the kidney’s medulla,99 percent of the water originally filtered from the blood in the Bowman’s capsule has been reabsorbed and returned to the body’s circulation.
等到过滤物（现在称为尿）到达肾脏髓质最深处（含盐）区域的收集小管部分时，99%从肾小囊的血液中最先滤过的水被重吸收回到身体循环。
Tubular Secretion
肾小管分泌
While the filtration and reabsorption activities of the kidneys’2million nephrons are removing salt and urea from the biood and forming urine, another process-tubular secretion-goes on simultaneously in both the proximal and distal tubules. Secretion removes a number of unwanted materials-including hydrogen ions, potassium ions, environmental pollutants like pesticides, and drug such as penicillin and Phenobarbital-from the blood in the capillaries surrounding the nephron and secretes them into the froming urine.
当肾脏中2百万肾单元的过滤与重吸收活动把盐和尿素从血液中移除，形成原尿时，另一个过程-管子的分泌，同时在近端小管和远端小管发生，分泌过程移除许多有害物质，包括氢离子，氯离子，环境污染物像杀虫剂，来自包绕肾单元和分泌形成原尿的毛细血管的血液中的青霉素，笨巴比妥等药品。
Tubular secretion is the physiological process that make drug testing possible-checking a person’s urine to see if he or she has taken drugs. Drug testing employs various laboratory techniques to detect even minute traces of the metabolic breakdown products of marijuana, cocaine, and many kinds of prescription drugs.
动运输来穿透细胞膜。在离子以这种方式被重新吸收时，原滤出液中80%-85%的水通过渗透过程又随之被动地返回毛细血管。
Next,the filtrate passes down the descending arm of the nephron’s U-shaped loop of Henle’s,which is bathed by an increasingly salty fluid. Water leaves the loop of Henle’s by osmosis and reenters the blood of the capillaries surrounding the tubule.The filtrate then rounds the bend in the loop of Henle’s and moves up the ascending arm and through the distal tubule ( far from the Bowman’s capsule) toward the collecting duct.
然后，滤出物通过肾单位里的U型 亨利袢降支，这个部位不断受到 盐分越来越多的液体的冲洗。水通过渗透作用离开亨利袢支，再输入小管周围的毛细血管中的血液。滤液绕行亨利袢支的弯曲部分，沿着升支向上移动，并通过远端小管（远离肾小囊 ），接近集合管。
The walls of the distal tubule are not permeable to water ,but those of the collecting duct are;and even though the filtrate passing through the duct is already quite concentrated, the surrounding tissues are even saltier.Thus, more water diffuses out of the collecting duct by osmosis and enters the blood of the surrounding capillaries.
水不能通过远曲小管的 管壁，但收集管的管壁允许水通过；虽然通过收集管的滤过液浓度已经很高，但周围组织含盐量更大。因此，更多的水通过渗透作用在集合管中扩散开，并且进入周围毛细血管中的血液。
By the time the filtrate now called urine has reached the part of the collecting tubule in the innermost (and saltiest) region of the kidney’s medulla,99 percent of the water originally filtered from the blood in the Bowman’s capsule has been reabsorbed and returned to the body’s circulation.
等到过滤物（现在称为尿）到达肾脏髓质最深处（含盐）区域的收集小管部分时，99%从肾小囊的血液中最先滤过的水被重吸收回到身体循环。
Tubular Secretion
肾小管分泌
While the filtration and reabsorption activities of the kidneys’2million nephrons are removing salt and urea from the biood and forming urine, another process-tubular secretion-goes on simultaneously in both the proximal and distal tubules. Secretion removes a number of unwanted materials-including hydrogen ions, potassium ions, environmental pollutants like pesticides, and drug such as penicillin and Phenobarbital-from the blood in the capillaries surrounding the nephron and secretes them into the froming urine.
当肾脏中2百万肾单元的过滤与重吸收活动把盐和尿素从血液中移除，形成原尿时，另一个过程-管子的分泌，同时在近端小管和远端小管发生，分泌过程移除许多有害物质，包括氢离子，氯离子，环境污染物像杀虫剂，来自包绕肾单元和分泌形成原尿的毛细血管的血液中的青霉素，笨巴比妥等药品。
Tubular secretion is the physiological process that make drug testing possible-checking a person’s urine to see if he or she has taken drugs. Drug testing employs various laboratory techniques to detect even minute traces of the metabolic breakdown products of marijuana, cocaine, and many kinds of prescription drugs.
管状分泌物是可能进行药物检测的生理过程-检查一个人的尿液，看他是否服药。药物检测使用各种实验室技术去察觉由新陈代谢故障产生的大麻，可卡因和许多指示药物的微小踪迹。
If a person takes a drug overdose and loses consciousness and no one is sure which drug was consumed, physicians quickly test the urine to identify the drug and determine the best treatment for saving the patient’s life. Two additional uses-testing athletes and employees for drug use in the playing field or on the job-are currently quite controversial.
如果一个人服药过多失去意识，没人确定他服用了哪种药物，内科医生讯速的检测尿去分辨药物从而决定最佳治疗方法去拯救病人的生命。两个额外的作用-检测运动员和员工在运动领域或工作中对药物的使用情况-在当前仍有争议。