Within the
nephron of the
kidney
The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...
, the descending limb of loop of Henle is the portion of the
renal tubule constituting the first part of the
loop of Henle.
Physiology
The permeability is as follows:
Also, the medullary
interstitium
The interstitium is a contiguous fluid-filled space existing between a structural barrier, such as a cell membrane or the skin, and internal structures, such as organs, including muscles and the circulatory system. The fluid in this space is ...
is highly concentrated (because of the activity of the ascending limb), leading to a strong
osmotic
Osmosis (, ) is the spontaneous net movement or diffusion of solvent molecules through a selectively-permeable membrane from a region of high water potential (region of lower solute concentration) to a region of low water potential (region ...
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.
Histology
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.
Nomenclature
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
Within the nephron of the kidney, the ascending limb of the loop of Henle is a segment of the heterogenous loop of Henle downstream of the descending limb, after the sharp bend of the loop. This part of the renal tubule is divided into a thin and ...
would be included.
Additional images
File:Gray1131.png, Longitudinal section of descending limb of Henle’s loop. a. Membrana propria. b. Epithelium.
References
Kidney anatomy
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