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1 GLOMERULAR FILTRATION (Kidney (nephron: functional unit of kidney…

- - - - blood filtration site
      - a network of capillaries
        
        retain cellular components & medium-to-high-molecular-weight proteins within the vasculature
        
        extruding glomerular filtrate nearly identical to plasma in its electrolyte & water composition
        
        glomerular filter rate (GFR)
        
        renal function parameter
        
        mL/min/kg
        
        glomerular tuft
        
        encased within Bowman's capsule
        
        area between is Bowman's space
        
        site of collection of glomerular filtrate
        
        funneled directly into first segment of proximal tubule
      - the structure is important in determining rate & selectivity of glomerular filtration
        
        wall of capillaries
        
        3 layers:
        
        1) capillary endothelium
        
        single layer of cells with cytoplasmic extensions
        
        pierced by fenestrae
        
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        2) basement membrane
        
        acellular
        
        arranged in 3 layers named according to their density with respect to alectron beam & their relative position
        
        lamina densa
        
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        lamina rara interna
        
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        lamina rara externa
        
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        3) visceral epithelium
        
        a layer of podocytes
        
        primary & secondary foot processes interdigitate with other foot processes from other podocytes and wrap around individual capillaries
        
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        creates barrier to the forces favouring & opposing filtration of blood
        
        forces favouring
        
        movement of water and solutes across glomerular capillary wall
        
        hydrostatic pressure of blood within capillary and oncotic pressure of fluid within Bowman's space (ultrafiltrate)
        
        forces opposing
        
        plasma oncotic pressure within glomerular capillary & hydrostatic pressure in Bowman's space
    - - site where filtered substances are absorbed from tubule fluid & secretion of plasma components into tubule fluid
    - - nephron merge into collecting duct segments
        
        traverse kidney and empties into renal pelvis
- - - - permeability of filtration barrier
        
        determined by structural & chemical characteristics of glomerular capillary wall
        
        selectively permeable
        
        size
        
        all cellular components & plasma proteins the size of albumin molecules /larger retained within bloodstream
        
        water & solutes are freely filtered
        
        net electrical charge
        
        cationic more freely filtered
        
        shape & deformability
        
        long, flexible molecules
        
        neutral dextran
      - surface area available for filtration
        
        product: ultrafiltration coefficient (KUF)
  - - - renal modulation of systemic blood pressure & intravascular volume
        
        renin-angiotensin-aldosterone system
        
        renin:
        
        release is stimulated by a decrease in renal perfusion pressure
        
        caused by systemic hypotension
        
        catalyzes transformation of angiotensinogen produced by liver to angiotensin I
        
        then converted to angiotensin II by angiotensin-converting enzyme (ACE)
        
        primarily in vascular endothelium of lung
        
        potent vasoconstrictor
        
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        directly activates sodium uptake in proximal tubule & collecting duct
        
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        stimulates production & release of vasodilative renal prostaglandins
        
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        release is suppressed by the improved renal perfusion & elevated plasma angiotensin II
        
        creates negative-feedback system
        
        mediated primarily through humoral factors
    - - renal blood flow, glomerular capillary pressure, KUF
        
        mediated by 2 autoregulatory systems
        
        control resistance to flow in afferent & efferent artterioles
        
        myogenic reflex
        
        glomerular arterioles respond to changes in arteriolar wall tension
        
        immediate afferent arteriolar constriction after an increase in arteriolar wall tension & arteriolar dilation after a decrease in arteriolar wall tension
        
        dilation & constriction respectively decrease and increase resistance to blood flow in afferent arteriole
        
        tubuloglomerular feedback
        
        increase in NaCl concentration in tubule fluid at macula densa causes signaling cascade in macula densa cells
        
        generate paracrine factors
        
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  - - - = rate of elimination of a substance divided by its plasma concentration
      - net clearance rate of a substance = (rates of flltration + secretion) - rate of absorption of the substance
        
        inulin as substance for measurement of clearance
        
        freely filtered by glomerulus but is neither reabsorbed nor secreted by renal tubule cells
        
        not produced by the body
        
        rate of its disappearance from blood after intravascular injection related to GFR
        
        creatinine
        
        byproduct of muscle metabolism
        
        similar to inulin
        
        Ccreatinine = Ucreatinine V / Pcreatinine