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    Acidification of Urine

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    Nanditha Suresh
    The kidney controls acid-base balance through 3 main mechanisms: 1) secretion of hydrogen ions, 2) reabsorption of filtered bicarbonate, and 3) production of new bicarbonate. Hydrogen ion secretion occurs along most of the nephron except the descending and ascending thin limbs of the loop of Henle. The late distal convoluted tubule and collecting duct are responsible for maximal acidification of urine through hydrogen ion secretion, lowering pH to as low as 4.5. Bicarbonate reabsorption is coupled to hydrogen ion secretion, with 80-90% occurring in the proximal convoluted tubule. New bicarbonate is produced through phosphate and ammonia buffers.

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    Acidification of Urine

    Uploaded by

    Nanditha Suresh
    219 views30 pages
    The kidney controls acid-base balance through 3 main mechanisms: 1) secretion of hydrogen ions, 2) reabsorption of filtered bicarbonate, and 3) production of new bicarbonate. Hydrogen ion secretion occurs along most of the nephron except the descending and ascending thin limbs of the loop of Henle. The late distal convoluted tubule and collecting duct are responsible for maximal acidification of urine through hydrogen ion secretion, lowering pH to as low as 4.5. Bicarbonate reabsorption is coupled to hydrogen ion secretion, with 80-90% occurring in the proximal convoluted tubule. New bicarbonate is produced through phosphate and ammonia buffers.

    Original Description:

    Renal system - MBBS 1st year

    Original Title

    Acidification of urine

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    The kidney controls acid-base balance through 3 main mechanisms: 1) secretion of hydrogen ions, 2) reabsorption of filtered bicarbonate, and 3) production of new bicarbonate. Hydrogen ion secretion occurs along most of the nephron except the descending and ascending thin limbs of the loop of Henle. The late distal convoluted tubule and collecting duct are responsible for maximal acidification of urine through hydrogen ion secretion, lowering pH to as low as 4.5. Bicarbonate reabsorption is coupled to hydrogen ion secretion, with 80-90% occurring in the proximal convoluted tubule. New bicarbonate is produced through phosphate and ammonia buffers.

    Copyright:

    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    219 views30 pages

    Acidification of Urine

    Uploaded by

    Nanditha Suresh
    The kidney controls acid-base balance through 3 main mechanisms: 1) secretion of hydrogen ions, 2) reabsorption of filtered bicarbonate, and 3) production of new bicarbonate. Hydrogen ion secretion occurs along most of the nephron except the descending and ascending thin limbs of the loop of Henle. The late distal convoluted tubule and collecting duct are responsible for maximal acidification of urine through hydrogen ion secretion, lowering pH to as low as 4.5. Bicarbonate reabsorption is coupled to hydrogen ion secretion, with 80-90% occurring in the proximal convoluted tubule. New bicarbonate is produced through phosphate and ammonia buffers.

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    © All Rights Reserved
    Download as PPT, PDF, TXT or read online from Scribd
    Download as ppt, pdf, or txt
    of 30

    Acidification of urine

    Renal control of Acid – Base


    balance
    • By excreting either acidic or basic
    urine by 3 mechanisms
    1. Secretion of H+
    2. Reabsorption of filtered
    HCO3-
    3. Production of new HCO3-
    H+ ion secretion
    • all parts of tubule except descending
    and ascending thin limb of LOH
    Late DCT and CD -Intercalated cells
    • H+ Secretion in Late DCT and CD is
    responsible for forming maximally
    acidic urine though only 5% of H+ is
    secreted .H+ concentration ↑ as
    much as 900-fold
    • In PT, H+ concentration↑ only about
    3-4fold although large amounts of H+
    are secreted
    Limiting pH
    • The maximal H+ gradient against
    which the transport mechanisms can
    secrete H+
    • pH 4.5 is thus the limiting pH
    corresponds to H+ concentration in
    the urine that is 1000 times the
    concentration in plasma
    • If no buffers that "tied up“ free
    H+ in the urine, limiting pH
    +
    reached rapidly, and H secretion
    stops
    pH Changes Along the
    Nephron
    Proximal Tubule Distal TUBULE
    • More H+ sec • Only 5% H+sec
    • H+ con can be ↑ • H+ con can be ↑
    to only 3-4 fold 900 fold
    pH Changes Along the
    Nephron
    Proximal Tubule Distal TUBULE
    • Not much • pH ↓to 4.5 –
    change in maximally acidic
    luminal pH as urine
    sec H+ reacts
    with HCO3_ to
    form H2CO3
    which breaks to
    Bicarbonate reabsorption
    Reabsorption of filtered bicarbonate-

    • Coupled to H+ ion secretion


    • 80-90% occurs in PCT
    • For each HCO3- reabsorbed from
    lumen, one HCO3- diffuses in to
    blood, though this is not the one that
    is reabsorbed from the tubule.
    Production of New HCO3-

    • Reaction with phosphate buffer-


    H+ excreted as titrable acid.
    +
    • Ammonia buffer- H excreted as
    NH4 +
    Phosphate Buffer-
    Phosphate Buffer
    • Consist of H2PO4 - and HPO42_
    • in DT & CD---bcoz phosphate which
    escapes proximal reabsorption is
    greatly concentrated by the
    reabsorption of water.
    Titrable acidity
    • Measure of acid excreted in urine by
    kidney
    • amount of NaH2PO4 present in urine
    determine titrable acidity of urine
    • As a result pH of urine is ↓
    Ammonia Buffer –
    PT,AscLOH,EarlyDT
    Ammonia Buffer-CD
    Diffusion trapping
    • NH3 is lipid-soluble and diffuses into
    CD lumen reacts with H+ to form
    NH4+
    • This lipid insoluble NH4+ is cannot
    pass into cell & stay back in tubular
    fluid
    • Trapping of NH4+ in tubular lumen of
    CD & is excreted in urine
    Non ionic Diffusion
    • Some weak acids & bases soluble in cell
    membrane in undissociated form & cross
    with difficulty in ionic form.
    • CD cells not permeable to NH4+ but
    permeable to NH3
    • Process by which NH3 secreted into urine
    & changed into NH4+ maintaining a
    concentration gradient for NH3 diffusion
    is called nonionic diffusion
    Regulation of H+ secretion
    • Most important stimuli for H+
    secretion is
    • ↑ Pco2 of ECF
    • ↑ H+ or a ↓ in HCO3-
    Aldosterone
    • stimulate Intercalated cells increase
    H+ secretion.
    • Conn,s syndrome- increased H+
    secretion-- increased HCO3
    reabsorption--- Alkalosis
    ↓ECF volume
    • stimulates H+ secretion & HCO3- and
    Na+ reabsorption by
    1. ↑Angiotensin II, which stimulates
    Na+- H+ exchanger
    2. ↑ Aldosterone levels
    ECF volume depletion causes Alkalosis
    K+
    • Hypokalemia- increased H+
    secretion, increased HCO3
    reabsorption Alkalosis
    • Hyperkalemia  decreased H+
    secretion, decreased HCO3
    reabsorption  Acidosis
    Acute renal failure Chronic renal
    • Onset – failure
    Sudden over • Gradual over
    days /weeks months or
    • Reversible years
    • Cause – • Irreversible
    Prerenal/postre • Renal/extraren
    nal al
    • Oliguria/anuria • Polyuria &
    nocturia
    Acute renal failure Chronic renalfailure
    Characteristic • Edema,
    features – Proteinuria,
    small sized
    • Sudden ↓ GFR
    kidneys
    • Rapid ↑ BP,
    Anaemia,
    urea
    Acidosis,hyperk
    &creatinine
    alemia,
    level
    hypertension,
    osteomalacia
    Treatment
    Acute renal failure Chronic
    • Dialysis – short renalfailure
    period • Chronic
    Maintenance
    dialysis
    • Renal
    transplantation
    Nephrotic syndrome

    • Glomerular permeability affected

    proteinuria---Hypoproteinemia

    Edema

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