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Urine concentrating mechanisms

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Urine concentrating mechanisms DR. EMAN EL ETER The kidney can excrete urine as dilute as 5 mOsm/L and as concentrate as high as 100-1400 mOsm/L. – PowerPoint PPT presentation

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Title: Urine concentrating mechanisms


1
Urine concentrating mechanisms
  • Dr. Eman El Eter

2
  • The kidney can excrete urine as dilute as 5
    mOsm/L and as concentrate as high as 100-1400
    mOsm/L.
  • The kidney can excrete large volume or small
    volume of urine without affecting the rate of
    solute excretion
  • What is the relation of ADH to urine osmolarity,
    i.e. diluted or concentrated urine?

3
Changes in the osmolarity of tubular fluid
throughout the nephrone
4
Changes in the osmolarity of tubular fluid
throughout the nephrone
5
Counter current multiplier mechanism
  • Responsible for the high osmolality of the renal
    medulla
  • 1200-1400 mOsm.
  • The renal medulla must accumulates solutes in
    great excess of water.
  • It is maintained by the balanced inflow and
    outflow of solutes and water in medulla.
  • A countercurrent mechanisms the inflow is
    parallel to, close to but opposite to outflow.

6
Mechanisms responsible for creation of
hyperosmolar medulla
  • 1- Active transport of Na and co-transport of
    K, Cl- and other ions out of loop of Henle into
    medullary interstitium.
  • 2- Active transport of ions from collecting ducts
    into medullary interstituim.
  • 3- Diffusion of large amounts of urea from the
    inner medullary collecting ducts into the
    medullary interstituim.
  • 4- Diffusion of only small amounts of water from
    the medullary collecting tubules into
  • the interstitium, less than the reabsorption of
    solutes into medullary interstitium.
  • 5- No water diffusion into the medulla from the
    ascending loop of Henle.

7
Counter current multiplier
ISF interstitial fluid
8
Counter current exchanger in the vasa recta
  • Function Maintains the hyperosmolarity of the
    renal medulla. Why?
  • Vasa Recta has two main features
  • 1- Blood flow is slow (1-2 of total renal blood
    flow).
  • 2- The vasa recta act as a counter current
    exchanger to minimize washout of solutes from the
    medullary interstitium. This is due to the U
    shape of vasa recta capillaries.

9
Disorders of urininary concentrating ability
  • Diabetes insipidus
  • Cause inability to produce or release ADH
  • Urine low fixed specific gravity (diluted urine)
  • Polyuria
  • Polydypsia.
  • Nephrogenic diabetes insipidus
  • Cause inability of kidney to respond to ADH
  • Diabetes mellitus
  • High specific gravity urine
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