Descending Limb of the Loop of Henle

The deeper regions of the medulla, around the tips of the loops of juxtamedullary nephrons, reach a concentration of 1,200 to 1,400 mOsm. In order to reach this high a concentration, the salt pumped out of the ascending limb must accumulate in the interstitial fluid of the medulla. This occurs because of the properties of the descending limb, to be discussed next, and because blood vessels around the loop do not carry back all of the extruded salt to the general circulation. The capillaries in the medulla are

Ascending limb of loop

Filtrate (tubular lumen)

Interstitial space

Apical membrane 2 Cl-

Apical membrane 2 Cl-

Na+ ATP ADP

Interstitial space

Loop Henle Human

■ Figure 17.15 The transport of ions in the ascending limb. In the thick segment of the ascending limb of the loop, Na+ and K+ together with two Cl- enter the tubule cells. Na+ is then actively transported out into the interstitial space and Cl- follows passively. The K+ diffuses back into the filtrate, and some also enters the interstitial space.

uniquely arranged to trap NaCl in the interstitial fluid, as will be discussed shortly.

The descending limb does not actively transport salt, and indeed is believed to be impermeable to the passive diffusion of salt. It is, however, permeable to water. Since the surrounding interstitial fluid is hypertonic to the filtrate in the descending limb, water is drawn out of the descending limb by osmosis and enters blood capillaries. The concentration of tubular fluid is thus increased, and its volume is decreased, as it descends toward the tips of the loops.

As a result of these passive transport processes in the descending limb, the fluid that "rounds the bend" at the tip of the loop has the same osmolality as that of the surrounding interstitial fluid (1,200 to 1,400 mOsm). There is, therefore, a higher salt concentration arriving in the ascending limb than there would be if the descending limb simply delivered isotonic fluid. Salt transport by the ascending limb is increased accordingly, so that the "saltiness" (NaCl concentration) of the interstitial fluid is multiplied (fig. 17.16).

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Responses

  • wegahta
    Does nacl get pumped out of the descending limb?
    8 years ago
  • almaz
    How does Na , K , Cl ions are transported in a thick ascending limb of loop of Henle?
    8 years ago
  • brhane muhammed
    Why there is hypertonic fluid in descending limb?
    2 years ago
  • jak
    What is the histo physiology of the thick descending limb of the loop of henle?
    2 years ago
  • katelyn
    What fluid in descending loop of henle is thus relative to capillaries?
    2 years ago
  • protasio
    Why is fluid isotonic in decending loop of henle?
    11 months ago
  • Tewolde
    How to identify ascending or descending limbs of a nephron loop?
    9 months ago
  • Nelida
    How has the descending limb of henle been adapted?
    9 months ago
  • dieter
    What is the function of the descending and ascending parts of the loop of henle in a nephron?
    9 months ago
  • awet
    How does na and cl move in the loop of henle?
    8 months ago
  • pandora banks
    What does the decending limb of henle do?
    4 months ago
  • LUKAS
    How ascending limb of loop of henle adjusts the conc of filtrate passed to thorught the medulla?
    4 months ago
  • gilly
    Why is there no acrive salt reabsorption in descending limb of loop on henle?
    2 months ago

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