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The kidney's ability to perform many of its functions depends on the three fundamental functions of filtration, reabsorption, and secretion, whose sum is called renal clearance or renal excretion. That is: Urinary excretion rate = Filtration rate – Reabsorption rate + Secretion rate [1]
Renal glucose reabsorption is the part of kidney (renal) physiology that deals with the retrieval of filtered glucose, preventing it from disappearing from the body through the urine. If glucose is not reabsorbed by the kidney, it appears in the urine, in a condition known as glycosuria. This is associated with diabetes mellitus. [1]
excretion = (filtration + secretion) - reabsorption; The proximal convoluted tubule of the nephron has protein channels that reabsorb glucose, and others that secrete para-aminohippuric acid (PAH). However, its ability to do so is proportionate to the channel proteins available for the transport. [citation needed]
Para-aminohippurate (PAH) clearance is a method used in renal physiology to measure renal plasma flow, which is a measure of renal function. [citation needed]PAH is completely removed from blood that passes through the kidneys (PAH undergoes both glomerular filtration and tubular secretion), and therefore the rate at which the kidneys can clear PAH from the blood reflects total renal plasma flow.
Reabsorption allows many useful solutes (primarily glucose and amino acids), salts and water that have passed through Bowman's capsule, to return to the circulation. These solutes are reabsorbed isotonically , in that the osmotic potential of the fluid leaving the proximal convoluted tubule is the same as that of the initial glomerular filtrate.
The collecting duct system is the final component of the kidney to influence the body's electrolyte and fluid balance. In humans, the system accounts for 4–5% of the kidney's reabsorption of sodium and 5% of the kidney's reabsorption of water. At times of extreme dehydration, over 24% of the filtered water may be reabsorbed in the collecting ...
Glycosuria is the excretion of glucose into the urine. Ordinarily, urine contains no glucose because the kidneys are able to reabsorb all of the filtered glucose from the tubular fluid back into the bloodstream. Glycosuria is nearly always caused by an elevated blood sugar level, most commonly due to untreated diabetes.
Further modification of ultrafiltrate, by reabsorption and secretion, transforms it into urine. Glomerular pressure is about 75 millimeters of mercury (10 kPa). It is opposed by osmotic pressure (30 mmHg, 4.0 kPa) and hydrostatic pressure (20 mmHg, 2.7 kPa) of solutes present in capsular space.