| Descending limb of loop of Henle | |
|---|---|
 Scheme of renal tubule and its vascular supply. (Labeled at center left.) | |
 Nephron ion flow diagram | |
| Details | |
| Identifiers | |
| Latin | pars descendens ansae nephricae |
| FMA | 17719 17705, 17719 |
| Anatomical terminology | |
Within thenephron of thekidney, thedescending limb of loop of Henle is the portion of therenal tubule constituting the first part of theloop of Henle.
The permeability is as follows:
| Substance | Permeability |
|---|---|
| ions | Low permeability.Sodium andchloride ions do not easily pass through.[1] |
| urea | Moderate permeability.[2] |
| water | Highly permeable. Water is readily reabsorbed from the descending limb by osmosis.[3] |
Also, the medullaryinterstitium is highly concentrated (because of the activity of the ascending limb), leading to a strongosmotic 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.[3]
The epithelium in the thick segment of the descending limb consists of lowsimple cuboidal cells, which resemble those found in theproximal tubule. In contrast, the epithelium transitions to a simple squamous type in the thin segment, which is less metabolically active and has minimal surface specializations. The presence ofaquaporin-1 channels in the thin segment facilitates high water permeability, crucial for water reabsorption as part of the kidney'scountercurrent exchange mechanism.[4][5]
They can be distinguished from thevasa recta by the absence of blood, and they can be distinguished from the thick ascending limb by the thickness of the epithelium.[6]
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, thethin ascending limb of loop of Henle would be included.
This article incorporates text in thepublic domain frompage 1223 of the 20th edition ofGray's Anatomy(1918)
