Lecture Notes Menu Urine Production


  1. FILTRATION

    1. RENAL FILTRATE IS PLASMA MINUS BLOOD CELLS AND BLOOD PROTEIN

    2. THE FILTRATION MEMBRANE IS FENESTRATED ENDOTHELIUM, BASEMENT MEMBRANE AND SLITLIKE PORES FORMED BY PODOCYTES

    3. FILTRATION PRESSURE IS RESPONSIBLE FOR FILTRATE FORMATION

      1. FILTRATION PRESSURE IS GLOMERULAR FILTRATION PRESSURE MINUS CAPSULE PRESSURE AND COLLOID OSMOTIC PRESSURE

      2. FILTRATION PRESSURE CHANGES ARE PRIMARILY CAUSED BY CHANGES IN GLOMERULAR PRESSURE

    4. THE GLOMERLUS ACTS AS AN ULTRA FILTER ALLOWING PASSAGE OF WATER, ELECTROLYTES, AND SMALL ORGANIC MOLECULES SUCH AS GLUCOSE

      1. TOTAL FILTRATE OF BOTH KIDNEYS AMOUNTS TO ABOUT 70 ML/MIN/SQ METER
      2. BOTH KIDNEYS CONTAIN APP 2 SQ METERS AREA
      3. THIS AMOUNT IS KNOWN AS GFR
      4. ABOUT 99 % IS RESORBED


  2. TUBULAR RESORPTION

    1. FILTRATE IS RESORBED BY PASSIVE TRANSPORT (SIMPLE AND FACILITATED DIFFUSION ) OR ACTIVE TRANSPORT INTO THE PERITUBULAR AREA

    2. SECTIONS OF THE TUBULES ARE SPECIALIZED
      1. THIN SEGMENT OF LOOP OF HENLE IS FOR PASSIVE TRANSPORT
      2. REMAINDER OF THE TUBULE IS FOR ACTIVE TRANSPORT AND PASSIVE TRANSPORT
    3. CLEARANCE IS THE REMOVAL OF SUBSTANCES FROM THE BLOOD PLASMA
      1. A SOLUTE IS NEVER FULLY REMOVED AT ONE TIME
      2. SEVERAL SWEEPS ARE NEEDED
      3. SUBSTANCES THAT ARE ELIMINATED RAPIDLY ARE CLEARED QUICKLY


      EXAMPLE OF CLEARANCE :

      550 mg X ARE EXCRETED AND THE PLASMA

      CONCENTRATION IS 1 mg/ml - THEN

      550 mg / min
      1mg/ml =

      550 ml CLEARED


    4. IF A SUBSTANCE IS NEITHER RESORBED OR SECRETED THEN ITS CLEARANCE IS A MEASURE OF GFR


  3. TUBULAR RESORPTION OF VARIOUS SUBSTANCES:


    1. EFFERENT ARTERIOLE IS NARROWER THAN THE PERITUBULAR CAVITY

    2. BLOOD FLOW TO THE PERITUBULAR CAVITY IS UNDER LOW PRESSURE

    3. THE WALL OF THE PERITUBULAR CAVITY IS VERY PERMEABLE

    4. MOST RESORPTION OCCURS IN THE PROXIMAL TUBULE

    5. THE EPITHELIAL CELLS POSSESS MICROVILLI TO INCREASE AREA

    6. GLUCOSE RESORPTION OCCURS BY THROUGH THE WALLS OF THE

      PROXIMAL TUBULE BY ACTIVE TRANSPORT

      1. WATER IS ABSORBED BY OSMOSIS

      2. ACTIVE TRANSPORT DEPENDS ON CARRIERS IN THE MEMBRANE

      3. IF MORE GLUCOSE IS PRESENT IN THE URINE THAN CAN BE CARRIED, IT HAS EXCEEDED ITS TRANSPORT CAPACITY

      4. THIS MECHANISM IS TERMED LIMITED TRANSPORT CAPACITY

      5. IF RENAL PLASMA THRESHOLD IS REACHED, GLUCOSE MAY BE PRESENT IN THE URINE

    7. AMINO ACIDS: ARE RESORBED BY AT LEAST THREE METHODS

      1. RESORBED IN PROXIMAL TUBULE

      2. ONLY A TRACE OF AMINO ACIDS ARE FOUND IN URINE

    8. SMALL PROTEIN MOLECULES ( ALBUMIN ) ARE RESORBED BY PINOCYTOSIS THROUGH THE MICROVILLI

      1. ONCE IN AN EPITHELIAL CELL THEY ARE CONVERTED TO AMINO ACIDS

      2. FROM HERE THEY MOVE INTO THE PERITUBULAR CAVITY

    9. WATER AND SODIUM RESORPTION :

      1. SUBSTANCES IN THE RENAL TUBULE TEND TO BECOME MORE CONCENTRATED WATER IS RESORBED

      2. MOST WATER RESORPTION OCCURS PASSIVELY BY OSMOSIS IN THE PROXIMAL AREA

      3. WATER ABSORPTION IS CLOSELY TIED TO Na TRANSPORT

      4. 70 % OF Na RESORPTION OCCURS IN THE PROXIMAL AREA BY Na PUMP ( ACTIVE TRANSPORT )

      5. AS POSITIVE CHARGED IONS MOVE ACROSS THE TUBULAR WALL , NEG CHARGED IONS ACCOMPANY THEM


        51 NEG IONS INCLUDE: Cl - HCO3 - PO4 - - -


      6. OCCURS BECAUSE OF ATTRACTION OF POS TO NEG

      7. THIS PROCESS IS PASSIVE TRANSPORT ( EX HCO3 - )

      8. AS MORE Na AND OTHER NEG IONS ARE TRANSPORTED INTO THE PERITUBULAR CAPILLARY, WATER FOLLOWS BY OSMOSIS ( HIGH - LOW )

      9. VOLUME OF FLUID IN RENAL TUBULE IS REDUCED BY AS MUCH AS 60 - 80 %

    10. BICARBONATE ABSORPTION

      1. RATE IS USUALLY ADJUSTED TO ALLOW A CONSTANT PLASMA HC03 - CONTENT

      2. RESORPTION OF HCO3 - IS ACTIVE TRANSPORT

      3. MEMBRANE IS NOT PERMEABLE TO HCO3 -

      4. IF HCO3 WERE NOT ABSORBED IT WOULD BE LIKE ADDING THE EQUIVALENT OF 4 L OF I N ACID TO THE BODY

      5. THIS HAS A FUNCTION IN PREVENTING ACIDOSIS

      6. THIS FUNCTION DOES NOT HAVE A FAST RATE OF ACIDOSIS FORMATION AS DOES THE RESPIRATORY SYSTEM

        FILTRATION AND RESORPTION IN THE NEPHRONS


        SUBSTANCE

        WATER
        Na
        K
        GLUCOSE
        AMINO ACIDS
        UREA

        FILTERED DAILY

        180 L
        26000 MEQ
        810 MEQ
        1000mM
        65 gm
        1280 mM

        URINE CONTENT

        1.5%
        150 MEQ
        100 MEQ
        ---
        2 gm
        500 MM

        NET RES

        99%
        99%
        88%
        100%
        98%
        60%


        FILTERATION

        Molecular WT

        5200
        30,000
        69,000

        Permeability

        100
        05
        005

        EXAMPLE SUBSTANCE

        INULIN
        VERY SMALL PROTIEN
        ALBUMIN
        H2O = 100


    EFFECT OF ADH ON CELL MEMBRANE OF LATE DISTAL TUBULES


    1. SECRETED FROM POSTERIOR PITUITARY ( NEUROHYPOPHYSIS )

    2. ACTIVATES ADENYL CYCLASE IN MEMBRANE

    3. c AMP FORMED

    4. DIFFUSES TO LUMINAL SIDE OF CELL

    5. ELONGATED VESICULAR STRUCTURES DEVELOP

    6. FUSE WITH CELLS MEMBRANE ( LUMINAL )

    7. PROVIDES AGGREGATES OF PROTEINS THAT ARE HYDROPHILIC H2O DIFFUSES OUT BY OSMOTIC PROCESS


    OSMORECEPTOR - ADH FEEDBACK CONTROL SYSTEM


    1. INCREASED OSMOLALITY EXCITES RECEPTORS LOCATED IN HYPOTHALAMUS

    2. SUPRA OPTIC NUCLEI IN HYPO CAUSE RELEASE OF ADH FROM POSTERIOR PITUITARY

    3. ADH CAUSES H2O CONSERVATION

    4. HYPO OSMOTIC STATE ACHIEVED - ADH DECREASED


    ARTERIAL PRESSURE ON URINARY OUTPUT IS: