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Urinary (Reabsorption (Water reabsorption (reabsorbed by paracellular…
Urinary
Reabsorption
uses diffusion, osmosis, or active transport
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moves from the lumen of the tubules and collecting ducts to blood within the peritubular capillaries and vasa recta
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Excess solutes waste products, some water remain in tubular fluid
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Transport of proteins
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proteins move across the membrane back into the blood by pinocytosis and receptor mediated endocytosis
Sodium reabsorption
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Na/K pumps embedded in the membrane keep Na low within the tubule cells. This is active transport that requires ATP
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Water reabsorption
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ADH binds to principal cells which increases aquaporins in the membrane near the end of the tubule. This in turn increases the water reabsorption from filtrate to blood and results in a smaller volume of more concentrated urine
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Secretion
movement of solutes, usually by active transport
Active transport—the movement of molecules via ATPase pumps that transport the substance through the renal epithelial cell into the lumen of the nephron.
Passive diffusion—the movement of molecules from the peritubular capillaries to the intersitial fluid within the nephron
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During secretion some substances±such as hydrogen ions, creatinine, and drugs—will be removed from the blood through the peritubular capillary network into the collecting duct. The end product of all these processes is urine, which is essentially a collection of substances that has not been reabsorbed during glomerular filtration or tubular reabsorbtion
The mechanisms by which secretion occurs are similar to those of reabsorption, however these processes occur in the opposite direction.
filtrate leaves the kidney through the ureter, and is stored in the bladder before being removed through the urethra. At this final stage it is only approximately one percent of the originally filtered volume, consisting mostly of water with highly diluted amounts of urea, creatinine, and variable concentrations of ions.
Excretion
Nitrogenous waste
urea, from protein breakdown
uric acid, from nucleic acid breakdown in liver
Creatinine, from creatinine metabolism in muscle
Drugs
penicillin, sulfonamides, aspirin
other metabolic wastes
urobilin, hormone metabolites
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