NationMaster - Encyclopedia: Glomerular filtration rate

Glomerular filtration rate (GFR) is the volume of fluid filtered from the renal (kidney) glomerular capillaries into the Bowman's capsule per unit time.^[1] Clinically, this is often measured to determine renal function. Compare to filtration fraction. The kidneys are organs that filter wastes (such as urea) from the blood and excrete them, along with water, as urine. ... The glomerulus is a capillary bed found surrounded by the Bowmans capsule of the nephron in the vertebrate kidney. ... The Bowmans capsule(other names: capsula glomeruli, glomerular capsule) is a cup like sac at the beginning of the tubular component of a nephron in the mammalian kidney. ... In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology. ... In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF). ...

Measurement

There are several different techniques used to calculate or estimate the glomerular filtration rate (GFR or eGFR).

Measurement using inulin

The GFR can be determined by injecting inulin (not insulin) into the plasma. Since inulin is neither reabsorbed nor secreted by the kidney after glomerular filtration, its rate of excretion is directly proportional to the rate of filtration of water and solutes across the glomerular filter. (Dr. Amir Khan) Note: This article title may be easily confused with insulin. ...

Estimation using creatinine clearance

In clinical practice however, creatinine clearance is used to measure GFR. Creatinine is an endogenous molecule, synthesized in the body, which is freely filtered by the glomerulus (but also secreted by the renal tubules in very small amounts). Creatinine clearance is therefore a close approximation of the GFR. However, the approximation of the GFR calculation is best measured by the evaluation and visualization of the frequency and duration of urination. The GFR is typically recorded in units of volume per time, e.g. milliliters per minute (ml/min). Creatinine clearance is a method that estimates the glomerular filtration rate (GFR) of the kidneys. ...

Example: A person has a plasma creatinine concentration of 0.01 mg/ml and in 1 hour he excretes 75 mg of creatinine in the urine. The GFR is calculated as M/P (where M is the mass of creatinine excreted per unit time and P is the plasma concentration of creatinine).

$mbox{GFR }= frac{frac{75mbox{ mg}}{60mbox{ mins}}}{0.01mbox{ mg}/mbox{ml}} = 125 mbox{ ml}/mbox{min}$

Estimation using Cockcroft-Gault formula

The Cockcroft-Gault formula may be used to calculate an Estimated Creatinine Clearance, which in turn estimates GFR:^[2]

$mbox{Creatinine clearance} = frac { mbox{(140 - Age)} times mbox{Mass (in kilograms)}} {mbox{72} times mbox{Plasma Creatinine (in mg/dl)}} times mbox{0.85 if female}$

MDRD formula

The MDRD formula estimates GFR using serum creatinine and age. Multipliers are used to adjust the estimation for race and gender.^[3]

$mbox{eGFR} = mbox{186} times mbox{Serum Creatinine}^{-1.154} times mbox{Age}^{-0.203} times mbox{1.21 if Black} times mbox{0.742 if Female}$

Calculation using Starling equation

It is also theoretically possible to calculate GFR using the Starling equation.^[4] Formulated in 1896 by the British physiologist Ernest Starling, the Starling equation illustrates the role of hydrostatic and oncotic forces (the so-called Starling forces) in the movement of fluid across capillary membranes. ...

The equation is used both in a general sense for all capillary flow, and in a specific sense for the glomerulus:

Note that

([P c - P i] - σ[π c - π i])

is the net driving force, and therefore the net filtration is proportional to the net driving force. Hydrostatic pressure is the pressure exerted by a fluid due to its weight. ... The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. ... The Efferent arterioles are a group of blood vessels that are part of the urinary system of many animals. ... In blood plasma, the dissolved compounds have an osmotic pressure. ... An abscess on the skin, showing the redness and swelling characteristic of inflammation. ...

In practice, it is not possible to identify the needed values for this equation, but the equation is still useful for understanding the factors which affect GFR, and providing a theoretical underpinning for the above calculations.

Normal ranges

GFR can increase due to hypoproteinemia because of the reduction in plasma oncotic pressure. GFR can also increase due to constriction of the efferent arteriole but decreases due to constriction of the afferent arteriole. Hypoproteinemia (or Hypoproteinaemia) is a condition where there is an abnormally low level of protein in the blood. ... The Efferent arterioles are a group of blood vessels that are part of the urinary system of many animals. ... The afferent arterioles are a group of blood vessels that supply the nephrons in many excretory systems. ...

See also

Renal failure is the condition in which the kidneys fail to function properly. ... In medicine, dialysis is a type of renal replacement therapy which is used to provide an artificial replacement for lost kidney function due to renal failure. ... In the physiology of the kidney, tubuloglomerular feedback (TGF) is one of several mechanisms the kidney uses to regulate glomerular filtration rate (GFR). ... In renal physiology, the filtration fraction is the ratio of the glomerular filtration rate (GFR) to the renal plasma flow (RPF). ...

References

In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 197th day of the year (198th in leap years) in the Gregorian calendar. ... In 1828 the Medical Academy of Georgia was chartered by the state of Georgia with plans to offer a single course of lectures leading to a bachelors degree. ...

External links

Category: Renal physiology The Family Practice Notebook is a medical database focused on family practice. ... It has been suggested that this article or section be merged into Excretory system. ... Human Physiology is the science of the mechanical, physical, and biochemical functions of humans in good health, their organs, and the cells of which they are composed. ... This illustration demonstrates the normal kidney physiology. ... Acid-base physiology is the study of the acids, bases and their reactions in the body. ... In chemistry, alchemy and water treatment, filtration is the process of using a filter to mechanically separate a mixture. ... Ultrafiltration (UF) is a variety of membrane filtration in which hydrostatic pressure forces a liquid against a semipermeable membrane. ... Countercurrent exchange is a mechanism used to transfer some component of a fluid from one flowing current of fluid to another across a permeable barrier between them. ... Arginine vasopressin (AVP), also known as argipressin or antidiuretic hormone (ADH), is a human hormone that is released when the body is low on water; it causes the kidneys to conserve water, but not salt, by concentrating the urine and reducing urine volume. ... Aldosterone is a steroid hormone (mineralocorticoid family) produced by the outer-section (zona glomerulosa) of the adrenal cortex in the adrenal gland to regulate sodium and potassium balance in the blood. ... Atrial natriuretic factor (ANF), atrial natriuretic peptide (ANP) or atriopeptin, is a polypeptide hormone involved in the homeostatic control of body water and sodium. ... The endocrine system is a control system of ductless endocrine glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. ... Renin, also known as angiotensinogenase, is a circulating enzyme (EC 3. ... Erythropoietin (IPA pronunciation: , alternative pronunciations: ) or EPO is a glycoprotein hormone that is a cytokine for erythrocyte (red blood cell) precursors in the bone marrow. ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... Chemical structure of prostaglandin E1 (PGE1). ... In medicine (nephrology) renal function is an indication of the state of the kidney and its role in physiology. ... In nephrology, dialysis adequacy is the measurement of renal dialysis for the purpose of determining dialysis treatment regime and to better understand the pathophysiology of renal dialysis. ... Creatinine clearance is a method that estimates the glomerular filtration rate (GFR) of the kidneys. ... The renal clearance ratio is found with the following equation: X is the analyte substance Cx is the renal plasma clearance of X Cin is the renal plasma clearance of inulin. ... The urea reduction ratio (URR), is a dimensionless number used to quantify hemodialysis treatment adequacy. ... Kt/V - a dimensionless number used to quantify hemodialysis and peritoneal dialysis treatment adequacy. ... Standardized Kt/V, also std Kt/V, is a way of measuring (renal) dialysis adequacy. ... Hemodialysis product (HDP) - is a number used to quantify hemodialysis and peritoneal dialysis treatment adequacy. ... Acid-base physiology is the study of the acids, bases and their reactions in the body. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... A Darrow Yannet diagram is a schematic used in physiology to identify how the volumes of extracellular fluid and intracellular fluid alter in response to conditions such as adrenal insufficiency and SIADH. It was developed in 1935. ... A significant fraction of the human body is water. ... Interstitial fluid (or tissue fluid, or intercellular fluid) is a solution which bathes and surrounds the cells of multicellular animals. ... In some animals, including mammals, the two types of extracellular fluids are interstitial fluid and blood plasma. ... The cytosol (cf. ... Blood plasma is the liquid component of blood, in which the blood cells are suspended. ... Transcellular fluid is the portion of total body water contained within epithelial lined spaces. ... In human physiology, the base excess (see: base) excess refers to the amount of acid required to return the blood pH of an individual to the normal value. ... In acid base physiology, the Davenport Diagram is a graphical tool, developed by Horace Davenport, that allows a clinician or investigator to describe blood bicarbonate concentrations and blood pH following a respiratory and/or metabolic acid-base disturbance. ... The anion gap is used to aid in the differential diagnosis of metabolic acidosis. ... The Bicarbonate buffering system is the most important buffer for mantaining a relatively constant pH in the plasma. ... Respiratory compensation is a mechanism by which plasma pH can be altered by varying the respiratory rate. ... Renal compensation is a mechanism by which the kidneys can regulate the plasma pH. It is slower than respiratory compensation, but has a greater ability to restore normal values. ...

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