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Excretion of drugs, Half life of Drugs, nephron - Coggle Diagram

- - - - foreign chemical compound in biological system, include drugs, drug metabolites, and environmental compounds that are not produced by the body.
- - - - Tubular reabsorption
        
        Occur after glomerular filtration; Take place along renal tubule
        
        increases half-life of drug
        
        2 mechanisms:
        
        Passive process: movement of ions and other atomic/molecular substances across cell membranes without need of energy input
        
        common for large number of exogenous substances (drugs)
        
        Lipophilic substances widely reabsorbed by passive tubular reabsorptio
        
        Active process: movement of molecules across membrane from lower concentration region to higher concentration region
        
        extra: important because it reabsorb nutrient and maintain electrolytes
        
        commonly seen with high threshold endogenous substances or nutrients (electrolytes, glucose, vitamins, amino acids)
        
        Prefer lipid-soluble drugs (most drugs are lipid-soluble)
        
        After metabolism of drugs in liver, drug become more polar (will change pH and charged in tubules), which prevent reabsorption of drugs
      - Tubular secretion
        
        carrier-mediated process; require energy
        
        capacity limited and saturable有限且饱和
        
        2 mechanisms:
        
        System for secretion of organic acids/anions (Salicylates, glucuronides, sulfates)
        
        System for secretion of organic bases/cations (Hexamethonium, histamine, morphine)
      - Glomerular filtration
        
        nonselective, unidirectional (one-direction) process
        
        Most drugs (ionised or unionised) are filtered, except those bound to plasma protiens (Albumin) or blood cells
        
        Driving force: Hydrostatic pressure of blood flowing in the capillaries
        
        Measurement: GFR (glomerular filtration rate); normal range: 110 - 130 ml/min
        
        About 10% of blood that enters glomerular is filtered
      - Excretion (1+2-3) / Renal clearance
        
        the excretion of drug into the urine by the kidneys; is the result of glomerular filtration, active tubular secretion and tubular reabsorption.
        
        Renal clearance less than product of GFR, renal absorption is assumed.
        
        Renal clearance more than product of GFR, tubular secretion is assumed.
    - - Blood pumped through kidney at high pressure
      - Most substances in fluid in blood filtered by the cell membrane of kidney
        
        Blood cells and large proteins are not filtered
        
        Most fluid and substances are reabsorbed back into the bloodstream
        
        All lipid-soluble substances
        
        Needed non-lipid soluble substances (glucose)
        
        Substances not absorbed are excreted in urine