{"content_id":"icp0uvsxos","slug":"nephron-structure-filtration-and-reabsorption","locale":"en","schema_type":"TechArticle","category":"knowledge_base","category_name":"Knowledge Base","title":"Nephron Structure and Filtrate Reabsorption","summary":"The nephron is the functional unit of the kidney that filters blood and returns needed substances. A calculation example shows the difference between filtrate and final urine, but kidney function cannot be assessed from urine volume alone.","sponsorship_disclosure":null,"affiliate_disclosure":null,"commerce_disclosure":null,"author":{"name":"Injoys Editorial Team","url":"https://injoys.com/ko/about"},"key_points":["Each kidney has about 1 million nephrons, but the number varies from person to person.","Filtrate produced in the glomerulus contains water and needed substances as well as waste products.","The tubules reabsorb needed substances and secrete some substances into the tubules.","Assuming 150 liters of filtrate and 1.5 liters of urine per day, the reabsorption rate is about 99%.","Kidney function is evaluated using both blood and urine tests, not urine volume alone."],"content_markdown":"A nephron is the smallest functional unit in the kidney that filters blood and produces urine. The initial filtrate formed by the glomerulus undergoes reabsorption in the tubules. As necessary substances return to the blood, the final urine volume becomes much smaller than the volume of the initial filtrate.\n\nThe nephron count is described based on NIDDK guidance reviewed in June 2018.\n\n## What Is a Nephron?\n\nA nephron is a microscopic structure responsible for filtration and the regulation of substances in the kidney. The kidneys are located on either side of the spine below the ribs. An adult kidney is generally about the size of a fist.\n\nEach kidney has about 1 million nephrons. Together, the two kidneys can be described as having about 2 million. This number is not the same for everyone. This is based on [NIDDK's explanation of kidney structure and function](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work).\n\nThe number of nephrons varies from person to person. A study of healthy kidney donors also observed differences by age. Older groups had fewer functioning nephrons. These findings can be found in the [study on nephron number and aging](https://pubmed.ncbi.nlm.nih.gov/27401688/).\n\n## Structure of the Glomerulus and Tubules\n\nA nephron consists of a renal corpuscle and a tubule. The renal corpuscle consists of the glomerulus and the Bowman's capsule surrounding it. The glomerulus contains a cluster of small blood vessels. The tubule is a thin tube through which filtered fluid travels.\n\n| Structure | Location or connection | Main role |\n|---|---|---|\n| Glomerulus | Cluster of capillaries within the renal corpuscle | Filters water and small substances from the blood |\n| Bowman's capsule | Structure surrounding the glomerulus | Receives filtrate and passes it to the tubule |\n| Tubule | Tube extending from Bowman's capsule | Regulates fluid composition through reabsorption and secretion |\n| Collecting duct | Duct connected to several nephrons | Helps regulate water and collects urine |\n\nThe tubules and ureters are different structures. The tubules regulate the composition of filtrate within the kidneys. The ureters carry urine produced by the kidneys to the bladder. The correct Korean term is ‘세뇨관,’ not ‘세노관.’\n\n## Comparing Blood Flow to the Kidneys and Initial Filtrate\n\nThe amount of blood entering the kidneys and the volume of initial filtrate are different measurements. About 25% of the blood pumped by the heart flows through the kidneys. This does not mean that 20% to 25% of the blood is discarded as urine. Blood passes through the kidneys repeatedly throughout the day.\n\n| Category | Meaning | Key distinction |\n|---|---|---|\n| Renal blood flow | Amount of blood entering the kidneys over a given period | Includes both blood cells and plasma |\n| Glomerular filtration rate | Amount of fluid filtered from plasma into Bowman's capsule | Different from the total amount of blood passing through the kidneys |\n| Final urine volume | Amount of fluid excreted after reabsorption and secretion | Much smaller than the initial filtrate first produced |\n\nInitial filtrate is the fluid first filtered by the glomerulus. A normal filtration barrier keeps blood cells and most large proteins in the blood vessels. Water and small substances can pass through this barrier. The distinction between blood flow and filtration volume is based on the [explanation of glomerular filtration rate physiology](https://www.ncbi.nlm.nih.gov/books/NBK500032/?report=reader).\n\n## How Do Filtration, Reabsorption, and Secretion Differ?\n\nFiltration is the process of producing initial filtrate from the blood. Reabsorption returns substances inside the tubule to the blood. Secretion moves substances from the blood into the tubule.\n\n| Process | Direction of substance movement | Typical example |\n|---|---|---|\n| Filtration | From blood in the glomerulus to Bowman's capsule | Water and small solutes enter the initial filtrate |\n| Reabsorption | From inside the tubule toward the blood | Recovery of water and necessary nutrients |\n| Secretion | From the blood into the tubule | Helps eliminate hydrogen ions and some drug components |\n\nThe glomerulus does not selectively filter only waste products. Initial filtrate also contains substances the body needs, such as glucose. Recovering these substances is the role of the tubules. The movement of substances in the tubules is regulated according to the body's condition.\n\nTherefore, the substances in urine are not determined by filtration alone. The amount excreted decreases depending on how much is reabsorbed. The amount secreted acts to increase excretion. This distinction is also explained in the [NIDDK workshop report on kidney function assessment](https://pmc.ncbi.nlm.nih.gov/articles/PMC12446987/).\n\n## Calculation Example Using 150 Liters of Initial Filtrate and 1.5 Liters of Urine\n\nAssuming 150 liters of initial filtrate and 1.5 liters of urine per day, the difference is 148.5 liters. This is a simple calculation for understanding the percentage reabsorbed. The two figures are not an individual's test results or criteria for determining what is normal.\n\n1. Set the daily initial filtrate volume at 150 liters.\n2. Set the final daily urine volume at 1.5 liters.\n3. The difference is 150 liters - 1.5 liters = 148.5 liters.\n4. The difference as a percentage of the initial filtrate is 148.5 ÷ 150 × 100 = 99%.\n\nIn this example, about 99% of the initial filtrate volume was reabsorbed. About 1% remained as final urine. This calculation explains the movement of water. It does not mean that 99% of all waste products are reabsorbed.\n\nThe actual daily filtration volume is not the same for everyone. Medical education materials sometimes describe it as about 180 liters per day. Urine volume is also affected by water intake and the amount lost through sweating, among other factors. This information can be found in the [explanation of glomerular filtration rate](https://www.ncbi.nlm.nih.gov/books/NBK500032/?report=reader) and [NIDDK's guide to the urinary tract](https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works).\n\n## The Kidneys' Role in Regulating Water and Electrolytes\n\nThe kidneys regulate the volume and composition of body fluids. Electrolytes are ions dissolved in body fluids, such as sodium and potassium. The kidneys regulate how much of these substances is excreted. They also help regulate blood acidity.\n\nKidney functions also include hormonal activity. The kidneys produce substances involved in regulating blood pressure. They also secrete a hormone that helps produce red blood cells. They help maintain bone health as well. These functions are described in [NIDDK's guide to kidney function](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work).\n\n## Common Mistakes About Initial Filtrate and Urine\n\nInterpreting initial filtrate volume as the amount of water to drink or as a health goal leads to incorrect conclusions. Most of the water in the initial filtrate returns to the blood. The figures and concepts below should each be understood differently.\n\n| Common misconception | Correct interpretation |\n|---|---|\n| If 150 liters of initial filtrate are produced per day, that much water must be consumed | Most of the water in the initial filtrate is reabsorbed, so it differs from water intake |\n| 1.5 liters of urine per day is the goal for everyone | This is an illustrative example, and urine volume varies among individuals |\n| The glomerulus retains all necessary substances | Small nutrients are also filtered and later reabsorbed |\n| Frequent urination means that nephrons are functioning well | Urination frequency is also affected by the bladder's storage capacity |\n| Urine is produced in the bladder | Urine is produced in the kidneys and stored in the bladder |\n\nUrine travels through the ureters and collects in the bladder. Urine stored in the bladder leaves the body through the urethra. Urine production and storage are different functions. This pathway can be found in [NIDDK's explanation of urinary tract anatomy](https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works).\n\n## Can Kidney Function Be Determined from Urine Volume Alone?\n\nUrine volume alone cannot determine whether kidney function is normal. The amount of water excreted is not the same indicator as the ability to remove waste products. Both blood and urine tests are used to assess kidney function.\n\n| Test indicator | What it measures | How it differs from urine volume |\n|---|---|---|\n| eGFR, the estimated glomerular filtration rate | Filtration function estimated from blood test results | Not a measurement of daily urine volume |\n| UACR, the urine albumin-creatinine ratio | The amount of albumin passing into the urine | A clue used to assess kidney damage |\n\nAlbumin is a protein found in the blood. When the kidneys are damaged, more albumin may be excreted in the urine. Test results are interpreted by considering not only a single measurement but also trends over time. The meaning of each test can be found in [NIDDK's guide to chronic kidney disease testing](https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis?dkrd=hispt1311).","content_html":"\u003cp\u003eA nephron is the smallest functional unit in the kidney that filters blood and produces urine. The initial filtrate formed by the glomerulus undergoes reabsorption in the tubules. As necessary substances return to the blood, the final urine volume becomes much smaller than the volume of the initial filtrate.\u003c/p\u003e\n\u003cp\u003eThe nephron count is described based on NIDDK guidance reviewed in June 2018.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#what-is-a-nephron\" class=\"anchor\" id=\"what-is-a-nephron\"\u003e\u003c/a\u003eWhat Is a Nephron?\u003c/h2\u003e\n\u003cp\u003eA nephron is a microscopic structure responsible for filtration and the regulation of substances in the kidney. The kidneys are located on either side of the spine below the ribs. An adult kidney is generally about the size of a fist.\u003c/p\u003e\n\u003cp\u003eEach kidney has about 1 million nephrons. Together, the two kidneys can be described as having about 2 million. This number is not the same for everyone. This is based on \u003ca href=\"https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work\"\u003eNIDDK's explanation of kidney structure and function\u003c/a\u003e.\u003c/p\u003e\n\u003cp\u003eThe number of nephrons varies from person to person. A study of healthy kidney donors also observed differences by age. Older groups had fewer functioning nephrons. These findings can be found in the \u003ca href=\"https://pubmed.ncbi.nlm.nih.gov/27401688/\"\u003estudy on nephron number and aging\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#structure-of-the-glomerulus-and-tubules\" class=\"anchor\" id=\"structure-of-the-glomerulus-and-tubules\"\u003e\u003c/a\u003eStructure of the Glomerulus and Tubules\u003c/h2\u003e\n\u003cp\u003eA nephron consists of a renal corpuscle and a tubule. The renal corpuscle consists of the glomerulus and the Bowman's capsule surrounding it. The glomerulus contains a cluster of small blood vessels. The tubule is a thin tube through which filtered fluid travels.\u003c/p\u003e\n\u003cdiv class=\"overflow-x-auto\"\u003e\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eStructure\u003c/th\u003e\n\u003cth\u003eLocation or connection\u003c/th\u003e\n\u003cth\u003eMain role\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Structure\"\u003eGlomerulus\u003c/td\u003e\n\u003ctd data-label=\"Location or connection\"\u003eCluster of capillaries within the renal corpuscle\u003c/td\u003e\n\u003ctd data-label=\"Main role\"\u003eFilters water and small substances from the blood\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Structure\"\u003eBowman's capsule\u003c/td\u003e\n\u003ctd data-label=\"Location or connection\"\u003eStructure surrounding the glomerulus\u003c/td\u003e\n\u003ctd data-label=\"Main role\"\u003eReceives filtrate and passes it to the tubule\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Structure\"\u003eTubule\u003c/td\u003e\n\u003ctd data-label=\"Location or connection\"\u003eTube extending from Bowman's capsule\u003c/td\u003e\n\u003ctd data-label=\"Main role\"\u003eRegulates fluid composition through reabsorption and secretion\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Structure\"\u003eCollecting duct\u003c/td\u003e\n\u003ctd data-label=\"Location or connection\"\u003eDuct connected to several nephrons\u003c/td\u003e\n\u003ctd data-label=\"Main role\"\u003eHelps regulate water and collects urine\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e\n\u003cp\u003eThe tubules and ureters are different structures. The tubules regulate the composition of filtrate within the kidneys. The ureters carry urine produced by the kidneys to the bladder. The correct Korean term is ‘세뇨관,’ not ‘세노관.’\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#comparing-blood-flow-to-the-kidneys-and-initial-filtrate\" class=\"anchor\" id=\"comparing-blood-flow-to-the-kidneys-and-initial-filtrate\"\u003e\u003c/a\u003eComparing Blood Flow to the Kidneys and Initial Filtrate\u003c/h2\u003e\n\u003cp\u003eThe amount of blood entering the kidneys and the volume of initial filtrate are different measurements. About 25% of the blood pumped by the heart flows through the kidneys. This does not mean that 20% to 25% of the blood is discarded as urine. Blood passes through the kidneys repeatedly throughout the day.\u003c/p\u003e\n\u003cdiv class=\"overflow-x-auto\"\u003e\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eCategory\u003c/th\u003e\n\u003cth\u003eMeaning\u003c/th\u003e\n\u003cth\u003eKey distinction\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Category\"\u003eRenal blood flow\u003c/td\u003e\n\u003ctd data-label=\"Meaning\"\u003eAmount of blood entering the kidneys over a given period\u003c/td\u003e\n\u003ctd data-label=\"Key distinction\"\u003eIncludes both blood cells and plasma\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Category\"\u003eGlomerular filtration rate\u003c/td\u003e\n\u003ctd data-label=\"Meaning\"\u003eAmount of fluid filtered from plasma into Bowman's capsule\u003c/td\u003e\n\u003ctd data-label=\"Key distinction\"\u003eDifferent from the total amount of blood passing through the kidneys\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Category\"\u003eFinal urine volume\u003c/td\u003e\n\u003ctd data-label=\"Meaning\"\u003eAmount of fluid excreted after reabsorption and secretion\u003c/td\u003e\n\u003ctd data-label=\"Key distinction\"\u003eMuch smaller than the initial filtrate first produced\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e\n\u003cp\u003eInitial filtrate is the fluid first filtered by the glomerulus. A normal filtration barrier keeps blood cells and most large proteins in the blood vessels. Water and small substances can pass through this barrier. The distinction between blood flow and filtration volume is based on the \u003ca href=\"https://www.ncbi.nlm.nih.gov/books/NBK500032/?report=reader\"\u003eexplanation of glomerular filtration rate physiology\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#how-do-filtration-reabsorption-and-secretion-differ\" class=\"anchor\" id=\"how-do-filtration-reabsorption-and-secretion-differ\"\u003e\u003c/a\u003eHow Do Filtration, Reabsorption, and Secretion Differ?\u003c/h2\u003e\n\u003cp\u003eFiltration is the process of producing initial filtrate from the blood. Reabsorption returns substances inside the tubule to the blood. Secretion moves substances from the blood into the tubule.\u003c/p\u003e\n\u003cdiv class=\"overflow-x-auto\"\u003e\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eProcess\u003c/th\u003e\n\u003cth\u003eDirection of substance movement\u003c/th\u003e\n\u003cth\u003eTypical example\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Process\"\u003eFiltration\u003c/td\u003e\n\u003ctd data-label=\"Direction of substance movement\"\u003eFrom blood in the glomerulus to Bowman's capsule\u003c/td\u003e\n\u003ctd data-label=\"Typical example\"\u003eWater and small solutes enter the initial filtrate\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Process\"\u003eReabsorption\u003c/td\u003e\n\u003ctd data-label=\"Direction of substance movement\"\u003eFrom inside the tubule toward the blood\u003c/td\u003e\n\u003ctd data-label=\"Typical example\"\u003eRecovery of water and necessary nutrients\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Process\"\u003eSecretion\u003c/td\u003e\n\u003ctd data-label=\"Direction of substance movement\"\u003eFrom the blood into the tubule\u003c/td\u003e\n\u003ctd data-label=\"Typical example\"\u003eHelps eliminate hydrogen ions and some drug components\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e\n\u003cp\u003eThe glomerulus does not selectively filter only waste products. Initial filtrate also contains substances the body needs, such as glucose. Recovering these substances is the role of the tubules. The movement of substances in the tubules is regulated according to the body's condition.\u003c/p\u003e\n\u003cp\u003eTherefore, the substances in urine are not determined by filtration alone. The amount excreted decreases depending on how much is reabsorbed. The amount secreted acts to increase excretion. This distinction is also explained in the \u003ca href=\"https://pmc.ncbi.nlm.nih.gov/articles/PMC12446987/\"\u003eNIDDK workshop report on kidney function assessment\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#calculation-example-using-150-liters-of-initial-filtrate-and-15-liters-of-urine\" class=\"anchor\" id=\"calculation-example-using-150-liters-of-initial-filtrate-and-15-liters-of-urine\"\u003e\u003c/a\u003eCalculation Example Using 150 Liters of Initial Filtrate and 1.5 Liters of Urine\u003c/h2\u003e\n\u003cp\u003eAssuming 150 liters of initial filtrate and 1.5 liters of urine per day, the difference is 148.5 liters. This is a simple calculation for understanding the percentage reabsorbed. The two figures are not an individual's test results or criteria for determining what is normal.\u003c/p\u003e\n\u003col\u003e\n\u003cli\u003eSet the daily initial filtrate volume at 150 liters.\u003c/li\u003e\n\u003cli\u003eSet the final daily urine volume at 1.5 liters.\u003c/li\u003e\n\u003cli\u003eThe difference is 150 liters - 1.5 liters = 148.5 liters.\u003c/li\u003e\n\u003cli\u003eThe difference as a percentage of the initial filtrate is 148.5 ÷ 150 × 100 = 99%.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eIn this example, about 99% of the initial filtrate volume was reabsorbed. About 1% remained as final urine. This calculation explains the movement of water. It does not mean that 99% of all waste products are reabsorbed.\u003c/p\u003e\n\u003cp\u003eThe actual daily filtration volume is not the same for everyone. Medical education materials sometimes describe it as about 180 liters per day. Urine volume is also affected by water intake and the amount lost through sweating, among other factors. This information can be found in the \u003ca href=\"https://www.ncbi.nlm.nih.gov/books/NBK500032/?report=reader\"\u003eexplanation of glomerular filtration rate\u003c/a\u003e and \u003ca href=\"https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works\"\u003eNIDDK's guide to the urinary tract\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#the-kidneys-role-in-regulating-water-and-electrolytes\" class=\"anchor\" id=\"the-kidneys-role-in-regulating-water-and-electrolytes\"\u003e\u003c/a\u003eThe Kidneys' Role in Regulating Water and Electrolytes\u003c/h2\u003e\n\u003cp\u003eThe kidneys regulate the volume and composition of body fluids. Electrolytes are ions dissolved in body fluids, such as sodium and potassium. The kidneys regulate how much of these substances is excreted. They also help regulate blood acidity.\u003c/p\u003e\n\u003cp\u003eKidney functions also include hormonal activity. The kidneys produce substances involved in regulating blood pressure. They also secrete a hormone that helps produce red blood cells. They help maintain bone health as well. These functions are described in \u003ca href=\"https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work\"\u003eNIDDK's guide to kidney function\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#common-mistakes-about-initial-filtrate-and-urine\" class=\"anchor\" id=\"common-mistakes-about-initial-filtrate-and-urine\"\u003e\u003c/a\u003eCommon Mistakes About Initial Filtrate and Urine\u003c/h2\u003e\n\u003cp\u003eInterpreting initial filtrate volume as the amount of water to drink or as a health goal leads to incorrect conclusions. Most of the water in the initial filtrate returns to the blood. The figures and concepts below should each be understood differently.\u003c/p\u003e\n\u003cdiv class=\"overflow-x-auto\"\u003e\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eCommon misconception\u003c/th\u003e\n\u003cth\u003eCorrect interpretation\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Common misconception\"\u003eIf 150 liters of initial filtrate are produced per day, that much water must be consumed\u003c/td\u003e\n\u003ctd data-label=\"Correct interpretation\"\u003eMost of the water in the initial filtrate is reabsorbed, so it differs from water intake\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Common misconception\"\u003e1.5 liters of urine per day is the goal for everyone\u003c/td\u003e\n\u003ctd data-label=\"Correct interpretation\"\u003eThis is an illustrative example, and urine volume varies among individuals\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Common misconception\"\u003eThe glomerulus retains all necessary substances\u003c/td\u003e\n\u003ctd data-label=\"Correct interpretation\"\u003eSmall nutrients are also filtered and later reabsorbed\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Common misconception\"\u003eFrequent urination means that nephrons are functioning well\u003c/td\u003e\n\u003ctd data-label=\"Correct interpretation\"\u003eUrination frequency is also affected by the bladder's storage capacity\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Common misconception\"\u003eUrine is produced in the bladder\u003c/td\u003e\n\u003ctd data-label=\"Correct interpretation\"\u003eUrine is produced in the kidneys and stored in the bladder\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e\n\u003cp\u003eUrine travels through the ureters and collects in the bladder. Urine stored in the bladder leaves the body through the urethra. Urine production and storage are different functions. This pathway can be found in \u003ca href=\"https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works\"\u003eNIDDK's explanation of urinary tract anatomy\u003c/a\u003e.\u003c/p\u003e\n\u003ch2\u003e\n\u003ca href=\"#can-kidney-function-be-determined-from-urine-volume-alone\" class=\"anchor\" id=\"can-kidney-function-be-determined-from-urine-volume-alone\"\u003e\u003c/a\u003eCan Kidney Function Be Determined from Urine Volume Alone?\u003c/h2\u003e\n\u003cp\u003eUrine volume alone cannot determine whether kidney function is normal. The amount of water excreted is not the same indicator as the ability to remove waste products. Both blood and urine tests are used to assess kidney function.\u003c/p\u003e\n\u003cdiv class=\"overflow-x-auto\"\u003e\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eTest indicator\u003c/th\u003e\n\u003cth\u003eWhat it measures\u003c/th\u003e\n\u003cth\u003eHow it differs from urine volume\u003c/th\u003e\n\u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Test indicator\"\u003eeGFR, the estimated glomerular filtration rate\u003c/td\u003e\n\u003ctd data-label=\"What it measures\"\u003eFiltration function estimated from blood test results\u003c/td\u003e\n\u003ctd data-label=\"How it differs from urine volume\"\u003eNot a measurement of daily urine volume\u003c/td\u003e\n\u003c/tr\u003e\n\u003ctr\u003e\n\u003ctd data-label=\"Test indicator\"\u003eUACR, the urine albumin-creatinine ratio\u003c/td\u003e\n\u003ctd data-label=\"What it measures\"\u003eThe amount of albumin passing into the urine\u003c/td\u003e\n\u003ctd data-label=\"How it differs from urine volume\"\u003eA clue used to assess kidney damage\u003c/td\u003e\n\u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\u003c/div\u003e\n\u003cp\u003eAlbumin is a protein found in the blood. When the kidneys are damaged, more albumin may be excreted in the urine. Test results are interpreted by considering not only a single measurement but also trends over time. The meaning of each test can be found in \u003ca href=\"https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis?dkrd=hispt1311\"\u003eNIDDK's guide to chronic kidney disease testing\u003c/a\u003e.\u003c/p\u003e\n","tags":["Kidney health","Health Screening","Kidney function"],"faqs":[{"question":"What is a nephron?","answer":"A nephron is the smallest functional unit of the kidney that performs filtration and regulates substances. The filtrate produced in the glomerulus passes through the renal tubule, where its composition is regulated."},{"question":"How many nephrons are in the kidneys?","answer":"Each kidney is described as having about 1 million nephrons. Together, both kidneys have about 2 million, but the number varies from person to person."},{"question":"Are the renal tubule and the ureter the same structure?","answer":"They are different structures. The renal tubule handles reabsorption and secretion within the kidney. The ureter carries urine from the kidney to the bladder."},{"question":"Does glomerular filtrate contain only waste products?","answer":"Glomerular filtrate contains necessary nutrients in addition to water and waste products. The necessary substances are reabsorbed into the blood from the renal tubule."},{"question":"Why is the final urine volume low even though there is a large amount of glomerular filtrate?","answer":"This is because most of the filtered water returns to the blood. The liquid that remains after this reabsorption process becomes the final urine."},{"question":"How are reabsorption and secretion different?","answer":"Reabsorption is the process of returning substances inside the tubule to the blood. Secretion is the movement of substances from the blood into the tubule."},{"question":"Must daily urine output be 1.5 liters?","answer":"1.5 liters is not a target amount that applies to everyone. Urine output varies depending on water intake and water lost through sweating, among other factors."},{"question":"If 150 liters of glomerular filtrate are produced each day, is that much water also needed?","answer":"The amount of glomerular filtrate should not be interpreted as the amount of water that must be consumed. Most of the water in the glomerular filtrate is reabsorbed and returns to the blood."},{"question":"Does the number of nephrons change with age?","answer":"Studies of healthy kidney donors found that older groups had fewer nephrons. However, findings from group studies cannot determine the number of nephrons in an individual."},{"question":"If urine passes normally, is kidney function also normal?","answer":"Urine output alone cannot determine whether kidney function is normal. Blood tests that estimate filtration function and urine tests that check for albumin are evaluated together."}],"sources":[{"url":"https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work","title":"NIDDK, Your Kidneys \u0026 How They Work","type":"source"},{"url":"https://www.niddk.nih.gov/health-information/urologic-diseases/urinary-tract-how-it-works","title":"NIDDK, The Urinary Tract \u0026 How It Works","type":"source"},{"url":"https://www.ncbi.nlm.nih.gov/books/NBK500032/?report=reader","title":"StatPearls, Physiology, Glomerular Filtration Rate","type":"data_point"},{"url":"https://pubmed.ncbi.nlm.nih.gov/27401688/","title":"The Substantial Loss of Nephrons in Healthy Human Kidneys with Aging","type":"data_point"},{"url":"https://pmc.ncbi.nlm.nih.gov/articles/PMC12446987/","title":"A Comprehensive Framework for Kidney Function Assessment: Summary of the NIDDK Reimagining Kidney Function Assessment Workshop","type":"source"},{"url":"https://www.niddk.nih.gov/health-information/kidney-disease/chronic-kidney-disease-ckd/tests-diagnosis?dkrd=hispt1311","title":"NIDDK, Chronic Kidney Disease Tests \u0026 Diagnosis","type":"source"}],"images":[{"id":1394,"url":"https://injoys.com/rails/active_storage/blobs/proxy/eyJfcmFpbHMiOnsiZGF0YSI6MjAwOTUsInB1ciI6ImJsb2JfaWQifX0=--c5c0f8cd2a52d2332af88ce5c19e090cae8a3cf0/ai-8a5db494.webp","is_representative":true,"generation_method":"ai_photo","license":"ai_generated","mime_type":"image/webp","width":1536,"height":1024,"translations":{"ko":{"alt":"실험실에서 빨간색과 파란색 액체가 흐르는 네프론 모형을 관찰하는 연구원","caption":"연구원이 네프론 모형으로 사구체 여과와 세뇨관의 원뇨 재흡수 과정을 살펴보고 있다.","description":null},"en":{"alt":"Researcher examining a nephron model with red and blue fluid flowing through clear tubes","caption":"The model demonstrates glomerular filtration and reabsorption along the renal tubules.","description":null},"ja":{"alt":"赤と青の液体が透明な管を流れるネフロン模型を観察する研究者","caption":"研究者が模型を使って糸球体濾過と尿細管での原尿再吸収を確認している。","description":null},"es":{"alt":"Investigadora observando un modelo de nefrona con líquidos rojo y azul en tubos transparentes","caption":"El modelo representa la filtración glomerular y la reabsorción en los túbulos renales.","description":null},"id":{"alt":"Peneliti mengamati model nefron dengan cairan merah dan biru yang mengalir dalam tabung bening","caption":"Model ini memperagakan filtrasi glomerulus dan reabsorpsi di sepanjang tubulus ginjal.","description":null},"pt":{"alt":"Pesquisadora observa um modelo de néfron com líquidos vermelho e azul em tubos transparentes","caption":"O modelo representa a filtração glomerular e a reabsorção ao longo dos túbulos renais.","description":null},"zh-hant":{"alt":"研究人員觀察透明管內流動紅藍液體的腎元模型","caption":"此模型呈現腎小球過濾與腎小管中原尿再吸收的過程。","description":null},"de":{"alt":"Forscherin betrachtet ein Nephronmodell mit roter und blauer Flüssigkeit in transparenten Röhren","caption":"Das Modell veranschaulicht die glomeruläre Filtration und Rückresorption in den Nierenkanälchen.","description":null}}},{"id":1395,"url":"https://injoys.com/rails/active_storage/blobs/proxy/eyJfcmFpbHMiOnsiZGF0YSI6MjAxMDEsInB1ciI6ImJsb2JfaWQifX0=--7d2b271036023a0ce7c2dbf0cbd8c3ea81332f90/ai-92b97a09.webp","is_representative":false,"generation_method":"ai_semi","license":"ai_generated","mime_type":"image/webp","width":1536,"height":1024,"translations":{"ko":{"alt":"신장 모형의 사구체와 세뇨관을 가리키며 설명하는 두 의료진","caption":"의료진이 신장 모형으로 네프론의 구조와 여과액 이동 경로를 살펴본다.","description":null},"en":{"alt":"Two clinicians examining the glomerulus and tubules on a kidney model","caption":"The clinicians use a kidney model to review nephron structure and the path of filtrate.","description":null},"ja":{"alt":"腎臓模型の糸球体と尿細管を指しながら確認する2人の医療従事者","caption":"腎臓模型を使ってネフロンの構造と濾液の流れを確認している。","description":null},"es":{"alt":"Dos profesionales señalan el glomérulo y los túbulos en un modelo de riñón","caption":"Los profesionales usan un modelo renal para revisar la nefrona y el recorrido del filtrado.","description":null},"id":{"alt":"Dua tenaga medis mengamati glomerulus dan tubulus pada model ginjal","caption":"Model ginjal digunakan untuk mempelajari struktur nefron dan aliran filtrat.","description":null},"pt":{"alt":"Dois profissionais apontam o glomérulo e os túbulos em um modelo de rim","caption":"Os profissionais usam o modelo renal para estudar o néfron e o trajeto do filtrado.","description":null},"zh-hant":{"alt":"兩名醫療人員查看腎臟模型上的腎小球與腎小管","caption":"醫療人員利用腎臟模型說明腎元結構與濾液的流動路徑。","description":null},"de":{"alt":"Zwei Fachkräfte betrachten Glomerulus und Tubuli an einem Nierenmodell","caption":"Das Nierenmodell veranschaulicht den Aufbau des Nephrons und den Weg des Filtrats.","description":null}}}],"published_at":"2026-09-19T15:09:46+09:00","updated_at":"2026-09-19T15:09:46+09:00","license":"cc_by","translation_status":"reviewed","available_locales":["ko","en","ja","es"],"data_locales":["ko","en","ja","es","id","pt","zh-hant","de"],"url":"https://injoys.com/en/articles/nephron-structure-filtration-and-reabsorption"}