The descending limb of loop of Henle
is the portion of the renal tubule
constituting the first part of the loop of Henle
The permeability is as follows:
Also, the medullary interstitium
is highly concentrated (because of the activity of the ascending limb), leading to a strong osmotic
gradient from the descending limb to the medulla.
Because of these factors, the concentration of the urine increases dramatically in the descending limb. Osmolality
can reach up to 1400 mOsmol/kg by the end of the descending limb.
The epithelium of the Thick segment is low simple cuboidal epithelium. The epithelium of the Thin segment is simple squamous
They can be distinguished from the vasa recta
by the absence of blood, and they can be distinguished from the thick ascending limb by the thickness of the epithelium.
Like the ascending limb, the descending limb has thick and thin portions. However, this distinction is not as important physiologically as in the ascending limb, so often the two are treated as one structure. The thick descending limb is less important than the thin descending limb, so often the terms "descending limb" and "thin descending limb" are used interchangeably.
Some sources simply refer to a "thin limb". In this context, the thin ascending limb of loop of Henle
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