The kidney is one of the most important organs in the body, performing numerous key functions such as excretion of waste products; regulation of blood pH, serum electrolyte concentrations, blood volume, and blood pressure; and the secretion of hormones such as erythropoietin (for synthesis of red blood cells), renin (for blood pressure control), and vitamin D (for bone health). The anatomy of the kidney is therefore complex in order to accomodate all these functions.
The basic functional unit of the kidney is known as the nephron. There are millions of nephrons in each kidney. One of the key components of a nephron is the glomerulus, which handles the filtration function of the kidney. Blood is carried into and out of the glomerulus via afferent and efferent arterioles. Surrounding the afferent arteriole is a filtration barrier, which allows fluid carrying wastes and electrolytes to pass through into what's known as Bowman's capsule, which is part of an extensive collecting system for that filtrate, commonly known as urine.
Kidney function is often measured by the glomerular filtration rate (GFR), which is the volume of fluid filtered across that filtration barrier per unit time. The GFR represents the total ability of the kidney (e.g. the sum of all glomeruli) to filter blood. Hence as we age, or as the kidney gets damaged in some disease process, nephrons begin to die, and the overall rate of filtration drops.
GFR is commonly estimated by the body's creatnine clearance. Creatnine (Cr) is a molecule synthesized by your muscles. It is freely filtered by the glomerulus and neither secreted (actually it is minimally secreted) nor reabsorbed into the urine. In other words, the only way for the body to get rid of creatnine is by filtering it through the glomerulus. Thus, measuring the creatnine filtration closely approximates the GFR. In the hospital, serum (blood) creatnine is routinely measured. A rise in serum creatnine may suggest a defect in glomerular filtration (i.e. if the glomerulus is not filtering properly, then creatnine cannot exit the body and therefore builds up in the blood).
Normal GFR is approximately 100 ml/min, with men usually having higher baseline GFR than women. Normal aging can decrease the GFR at an approximate rate of 1 ml/min per year after the age of 30. Various disease processes (e.g. diabetes, hypertension, lupus, etc) can reduce kidney function. Whatever the disease process, renal disease may be classified into 5 stages, based on the GFR:
Stage 1: GFR > 90. Kidneys are largely intact, and treatment is aimed at halting the disease process to preserve kidney function.
Stage 2: GFR between 60-90. Kidney function has declined slightly, and treatment is still aimed at halting the disease process.
Stage 3: GFR between 30-60. Kidney function is significantly compromised. Anemia and bone problems occur with higher frequency (recall that the kidney is responsible for synthesizing erythropoietin and vitamin D).
Stage 4: GFR between 15-30. Kidney function is severely compromised. At this stage, you have to make preparations for dialysis and think about a kidney transplant.
Stage 5: GFR < 15. This is also known as end stage renal disease By this point, your kidneys no longer have sufficient filtration capacity to maintain life, and you will need dialysis or a transplant.
The kidney is an organ that cannot regenerate or repair itself (at least with current medical technology); whatever is lost is lost forever. So treat your kidneys well!
The basic functional unit of the kidney is known as the nephron. There are millions of nephrons in each kidney. One of the key components of a nephron is the glomerulus, which handles the filtration function of the kidney. Blood is carried into and out of the glomerulus via afferent and efferent arterioles. Surrounding the afferent arteriole is a filtration barrier, which allows fluid carrying wastes and electrolytes to pass through into what's known as Bowman's capsule, which is part of an extensive collecting system for that filtrate, commonly known as urine.
Kidney function is often measured by the glomerular filtration rate (GFR), which is the volume of fluid filtered across that filtration barrier per unit time. The GFR represents the total ability of the kidney (e.g. the sum of all glomeruli) to filter blood. Hence as we age, or as the kidney gets damaged in some disease process, nephrons begin to die, and the overall rate of filtration drops.
GFR is commonly estimated by the body's creatnine clearance. Creatnine (Cr) is a molecule synthesized by your muscles. It is freely filtered by the glomerulus and neither secreted (actually it is minimally secreted) nor reabsorbed into the urine. In other words, the only way for the body to get rid of creatnine is by filtering it through the glomerulus. Thus, measuring the creatnine filtration closely approximates the GFR. In the hospital, serum (blood) creatnine is routinely measured. A rise in serum creatnine may suggest a defect in glomerular filtration (i.e. if the glomerulus is not filtering properly, then creatnine cannot exit the body and therefore builds up in the blood).
Normal GFR is approximately 100 ml/min, with men usually having higher baseline GFR than women. Normal aging can decrease the GFR at an approximate rate of 1 ml/min per year after the age of 30. Various disease processes (e.g. diabetes, hypertension, lupus, etc) can reduce kidney function. Whatever the disease process, renal disease may be classified into 5 stages, based on the GFR:
Stage 1: GFR > 90. Kidneys are largely intact, and treatment is aimed at halting the disease process to preserve kidney function.
Stage 2: GFR between 60-90. Kidney function has declined slightly, and treatment is still aimed at halting the disease process.
Stage 3: GFR between 30-60. Kidney function is significantly compromised. Anemia and bone problems occur with higher frequency (recall that the kidney is responsible for synthesizing erythropoietin and vitamin D).
Stage 4: GFR between 15-30. Kidney function is severely compromised. At this stage, you have to make preparations for dialysis and think about a kidney transplant.
Stage 5: GFR < 15. This is also known as end stage renal disease By this point, your kidneys no longer have sufficient filtration capacity to maintain life, and you will need dialysis or a transplant.
The kidney is an organ that cannot regenerate or repair itself (at least with current medical technology); whatever is lost is lost forever. So treat your kidneys well!
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