Urine Formatio1 - of the glomerular podocytes and the...

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Urine Formation The production of urine begins with filtration of the blood moving through the the glomerulus. As the filtrate passes through the PCT, nephron loop and DCT, many useful substances are reabsorbed back into the blood; other substances are actively secreted into the filtrate for elimination. The last step of urine formation is the concentration of wastes and conservation of water by the removal of water from the filtrate to be returned to the blood. For males, the kidneys will make about 180 L or urine/day and females about 150 L of urine/day. Obviously, people do not urinate 100s of liters each day, so the majority of the fluid in the filtrate is reabsorbed in the PCT, DCT and CD and only 1 to 2 L of urine is excreted. Filtration Filtration Membrane Filtration is the process of separating substances based upon shape, size and charge. Within the glomerular capsule is a specialized membrane through which filtered substances must pass. This so-called filtration membrane consists of the capillary endothelial cells, the pedicels
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Unformatted text preview: of the glomerular podocytes and the basement membranes between the two. Unlike the capillaries found in most tissues, the capillaries in the kidneys are fenestrated . These pores exclude relatively large substances like the cellular components of blood which remain in the blood capillaries. The basement membranes are a proteoglycan gel which has a large negative charge. The basement membrane can exclude most large molecules . Thus, blood plasma consists of ~7% protein while the glomerular filtrate is only about 0.03% protein. The last component of the filtration membrane is formed by the cells of the glomerular capsule. These podocytes extend pedicels that cover the capillaries. Between the pedicels are negatively charged filtration slits that exclude particles > 3nm. A healthy filtration membrane ensures that only water and very small solutes are filtered out of the blood....
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Urine Formatio1 - of the glomerular podocytes and the...

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