This mass equals the mass filtered at the glomerulus as nothing is added or removed in the nephron. Relating this principle to the below equation – for the substance used, the product of urine concentration and urine flow equals the mass of substance excreted during the time that urine has been collected. The rate therefore measured is the quantity of the substance in the urine that originated from a calculable volume of blood. GFR is equal to the renal clearance ratio when any solute is freely filtered and is neither reabsorbed nor secreted by the kidneys. In other words, the filtration rate is dependent on the difference between the higher blood pressure created by vasoconstriction of the input or afferent arteriole versus the lower blood pressure created by lesser vasoconstriction of the output or efferent arteriole. Ĭentral to the physiologic maintenance of GFR is the differential basal tone of the afferent and efferent arterioles (see diagram). Staging of chronic kidney disease is based on categories of GFR as well as albuminuria and cause of kidney disease. Both GFR and C Cr may be accurately calculated by comparative measurements of substances in the blood and urine, or estimated by formulas using just a blood test result ( eGFR and eC Cr) The results of these tests are used to assess the excretory function of the kidneys. Creatinine clearance exceeds GFR due to creatinine secretion, which can be blocked by cimetidine. Creatinine clearance is the volume of blood plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. The glomerular filtration rate (GFR) describes the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time. Other tests that can assess the function of the kidneys include assessment of electrolyte levels such as potassium and phosphate, assessment of acid-base status by the measurement of bicarbonate levels from a vein, and assessment of the full blood count for anaemia. One of the measures of kidney function is the glomerular filtration rate (GFR). These include tests that are intended to directly measure the function of the kidneys, as well as tests that assess the function of the kidneys by looking for evidence of problems associated with abnormal function. Blood tests īlood tests are also used to assess kidney function. The ability of the kidneys to filter protein is often measured, as urine albumin or urine protein levels, measured either at a single instance or, because of variation throughout the day, as 24-hour urine tests. Abnormal kidney function may cause too much or too little urine to be produced. Part of the assessment of kidney function includes the measurement of urine and its contents. If the kidneys are unable to excrete urea, a person may develop a widespread itch or confusion. They may develop evidence of chronic kidney disease, that can be used to assess its severity, for example high blood pressure, osteoporosis or anaemia. For example, a person with chronic kidney disease may develop oedema due to failure of the kidneys to regulate water balance. This is because a person with abnormally functioning kidneys may have symptoms that develop. A global assessment of renal function is often ascertained by estimating the rate of filtration, called the glomerular filtration rate (GFR).Ĭlinical assessment can be used to assess the function of the kidneys. This is performed at the microscopic level by many hundreds of thousands of filtration units called renal corpuscles, each of which is composed of a glomerulus and a Bowman's capsule. Proper function of the kidney requires that it receives and adequately filters blood. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. Each nephron begins with a filtration component that filters the blood entering the kidney. Much of renal physiology is studied at the level of the nephron, the smallest functional unit of the kidney. The functions of the kidney include maintenance of acid-base balance regulation of fluid balance regulation of sodium, potassium, and other electrolytes clearance of toxins absorption of glucose, amino acids, and other small molecules regulation of blood pressure production of various hormones, such as erythropoietin and activation of vitamin D.
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