renal clearance
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Introduction
Excretion of molecules (drugs, metabolites, biomolecules) in the urine by the kidney involves:
- glomerular filtration
- tubular secretion (active)
- tubular resorption (passive)
Glomerular filtration depends on glomerular filtration rate & protein binding.
In the proximal renal tubule, anionic & cationic carrier- mediated transport occur. Organic acids are secreted by the anionic transport; organic bases are secreted by the cationic transport. These carrier systems are rather non-selective & can be bidirectional.*
In the proximal & distal tubules, non-ionized weak organic acids & bases are passively resorbed (pH-dependent). The concentration gradient for passive bak-diffusion is created by resorption of H2O with Na+ & other inorganic ions.
* transport is predominantly secretory
uric acid is bidirectionally transported
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References
- ↑ The Pharmacological Basis of Therapeutics, 9th ed. Gilman et al, eds. Permagon Press/McGraw Hill, 1996 pg 17