Lecture Notes Menu Glomerular Filtration Mechanism


  1. URINE FORMATION BEGINS WHEN WATER AND OTHER MATERIALS ARE FILTERED OUT OF THE BLOOD PLASMA

    1. FILTERED OUT OF THE GLOMERULAR CAPILLARIES INTO THE BOWMANS CAPSULE

    2. THE CAPILLARIES ARE HIGHLY PERMEABLE

    3. THE FORCE RESPONSIBLE FOR MOVEMENT THROUGH THE CAPILLARIES IS HYDROSTATIC PRESSURE FROM THE BLOOD SYSTEM

    4. THIS PRESSURE IS KNOWN AS GLOMERULAR HYDROSTATIC PRESSURE

    5. THIS PRESSURE IS ALSO INFLUENCED BY THE OSMOTIC PRESSURE IN THE GLOMERULUS AND THE HYDROSTATIC PRESSURE IN THE INSIDE THE BOWMANS CAPSULE


      FILTRATION PRESSURE = GLOMERULAR HYDROSTATIC PRESSURE - PLASMA BOWMAN OSMOTIC +HYDRO PRESSURE PRESS


    6. THE RESULTING FILTRATE HAS ABOUT THE SAME COMPOSITION AS TISSUE FLUID ELSEWHERE EXCEPT FOR LARGE MOLECULES (PROTEIN, BLOOD CELLS ETC )

  2. FILTRATION RATE AND REGULATION

    1. GLOMERULAR FILTRATION IS DIRECTLY RELATED TO FILTRATION PRESSURE

    2. THE GLOMERULAR CAPILLARY IS LOCATED BETWEEN THE AFFERENT AND EFFERENT ARTERIOLES

    3. ANY CHANGE IN THE DIAMETER OF THESE WILL AFFECT PRESSURE

    4. THIS WILL CHANGE THE GFR

      EXAMPLE:

      AFFERENT ARTERY CONSTRICTS - GFR DROPS

      EFFERENT ARTERY CONSTRICTS - GFR INCREASES

      SYMPATHETIC NERVE IMPULSE REGULATES PROCESS

      DILATION MAY ALSO OCCUR


    5. BLOOD FLOW THROUGH GLOMERULUS CAN ALSO AFFECT GFR

      1. IN CAPILLARIES THE HYDROSTATIC PRESSURE IS OPPOSED BY THE OSMOTIC PRESSURE OF THE PLASMA IN THE GLOMERULUS

      2. HYDROSTATIC PRESSURE WILL FORCE OUT WATER WHILE THE OSMOTIC PRESSURE ATTRACTS WATER INWARD

      3. AS FILTRATION CONTINUES, THE PROTEINS THAT REMAIN IN THE PLASMA CAUSE OSMOTICPRESSURE IN THE GLOMERULUS TO RISE

      4. WHEN THIS PRESSURE REACHES A CERTAIN LEVEL FILTRATION STOPS

      5. AS BLOOD FLOWS SLOWLY A LARGER PART OF THE PLASMA IS FILTERS OUT OF THE GLOMERULUS AND OSMOTIC PRESSURE IS GREATER

      6. IF FLOW IS RAPID, LESS FILTERS OUT AND OSMOTIC PRESSURE IS LESS

    6. BOWMANS CAPSULE CAN ALSO AFFECT GFR

      1. CAPSULAR PRESSURE CAN CHANGE AS RESULT OF OBSTRUCTIONS

      2. THE CAUSES A BACKUP OF FLUID

      3. GFR MAY DROP


  3. REGULATION OF FILTRATION PRESSURE

    1. DECREASING FILTRATION RATE THE Cl - IONS REACHING THE MACULA DENSA DECREASE

    2. MACULA DENSA CAUSES SMOOTH MUSCLE IN THE WALL OF THE AFFERENT ARTERIOLE TO BECOME DILATED

    3. MORE BLOOD FLOWS INTO THE GLOMERULUS

    4. THE INCREASE IN GLOMERULAR PRESSURE CAUSES THE GFR TO RISE

    5. JUXTAGLOMERULAR CELLS RELEASE RENNIN

    6. THIS CAUSES THE FORMATION OF ANGIOTENSIN I, WHICH IS QUICKLY CHANGED INTO ANGIOSTENSIN II

    7. THIS CAUSES THE MUSCLE IN THE EFFERENT ARTERIOLE TO CONSTRICT

    8. THIS PROCESS IS KNOWN AS AUTOREGULATION