View source for Descending limb of loop of Henle

{{Short description|Part of kidney anatomy}}
{{Infobox anatomy
| Name        = Descending limb of loop of Henle
| Latin       = pars descendens ansae nephricae
| Image       = Gray1128.png
| Caption     = Scheme of renal tubule and its vascular supply. (Labeled at center left.)
| Image2      = Kidney_nephron_molar_transport_diagram.png
| Caption2    = Nephron ion flow diagram
| Precursor   =
| System      =
| Artery      =
| Vein        =
| Nerve       =
| Lymph       =
}}
Within the [[nephron]] of the [[kidney]], the '''descending limb of loop of Henle''' is the portion of the [[nephron#Renal tubule|renal tubule]] constituting the first part of the [[loop of Henle]].
==Physiology==
The permeability is as follows:
{| class="wikitable"
! Substance !! Permeability
|-
| [[ions]]  || Low permeability. [[Sodium]] and [[chloride]] ions do not easily pass through.<ref>{{Cite web |url=http://clem.mscd.edu/~raoa/bio2320/uriphys/sld019.htm |title=a.The descending limb of the loop of Henle is highly permeable to water and relatively impermeable to solutes such as Na and Cl<!-- Bot generated title --> |access-date=2006-11-25 |archive-url=https://web.archive.org/web/20060519172906/http://clem.mscd.edu/~raoa/bio2320/uriphys/sld019.htm |archive-date=2006-05-19 |url-status=dead }}</ref>
|-
| [[urea]] || Moderate permeability.<ref>{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 7/7ch08/7ch08p09 |chapter-url=http://humanphysiology.tuars.com/program/section7/7ch08/7ch08p09.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section7/7ch08/7ch08p09.htm|archive-date=2016-03-24}}</ref>
|-
| [[water]] || Highly permeable. Water is readily reabsorbed from the descending limb by osmosis.<ref name="gp7ch07p09">{{cite book| title= Essentials of Human Physiology| first= Thomas M. |last= Nosek| chapter=Section 7/7ch07/7ch07p09 |chapter-url=http://humanphysiology.tuars.com/program/section7/7ch07/7ch07p09.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section7/7ch07/7ch07p09.htm|archive-date=2016-03-24}}</ref>
|}
Also, the medullary [[interstitium]] is highly concentrated (because of the activity of the ascending limb), leading to a strong [[osmosis|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.<ref name="gp7ch07p09" />
==Histology==
The epithelium of the Thick segment is low simple cuboidal epithelium.  The epithelium of the Thin segment is [[Simple squamous epithelium|simple squamous]].<ref>{{Cite web |url=https://histo.life.illinois.edu/histo/lab/kidney/kidney.htm |title=University of Illinois College of Medicine |access-date=2009-12-04 |archive-date=2010-07-08 |archive-url=https://web.archive.org/web/20100708075740/https://histo.life.illinois.edu/histo/lab/kidney/kidney.htm |url-status=dead }}</ref>
They can be distinguished from the [[Straight arterioles of kidney|vasa recta]] by the absence of blood, and they can be distinguished from the thick ascending limb by the thickness of the epithelium.<ref>{{BUHistology|15804loa|inline=1}}</ref>
==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]] would be included.
==Additional images==
<gallery>
File:Gray1131.png|Longitudinal section of descending limb of Henle's loop. a. Membrana propria. b. Epithelium.
</gallery>
==References==
{{Gray's}}
<references />
{{Kidney}}
[[Category:Kidney anatomy]]
{{Portal bar|Anatomy}}