Editing Nephron (section)

== Structure ==
[[File:Physiology of Nephron.png|260px|thumb|right|Fig.1) Schematic diagram of the nephron (yellow), relevant circulation (red/blue), and the four methods of altering the filtrate.]]
The nephron is the functional unit of the kidney.<ref name="Pocock">{{cite book| vauthors = Pocock G, Richards CD |title=Human physiology : the basis of medicine|date=2006|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-856878-0|page=349|edition=3rd}}</ref>  This means that each separate nephron is where the main work of the kidney is performed.

A nephron is made of two parts:
* a [[renal corpuscle]], which is the initial filtering component, and
* a [[renal tubule]] that processes and carries away the [[Filtration|filtered fluid]].<ref name="tortora">{{Cite book|title=Principles of anatomy and physiology| vauthors = Tortora GJ, Derrickson BH |date=2010|publisher=John Wiley & Sons |isbn=978-0-470-23347-4|edition=12th|location=Hoboken, NJ|oclc=192027371}}</ref>{{rp|1024}}

=== Renal corpuscle ===
{{Main article|Renal corpuscle}}
[[File:Filtration barrier.svg|thumb|260px|Fig.2) Schematic of the glomerular filtration barrier (GFB).
A. The endothelial cells of the glomerulus; 1. endothelial pore (fenestra).<br /> B. [[Glomerular basement membrane]]: 1. lamina rara interna 2. lamina densa 3. lamina rara externa <br />
C. Podocytes: 1. enzymatic and structural proteins 2. filtration slit 3. diaphragm]]

The renal corpuscle is the site of the filtration of [[blood plasma]]. The renal corpuscle consists of the [[glomerulus (kidney)|glomerulus]], and the glomerular capsule or [[Bowman's capsule]].<ref name="tortora" />{{rp|1027}}

The renal corpuscle has two poles: a vascular pole and a tubular pole.<ref name="junqueiras">{{cite book | vauthors = Mescher AL |year=2016 |title=Junqueira's Basic Histology | edition = 14th  |publisher=Lange | isbn = 978-0-07-184268-6 }}</ref>{{rp|397}} The arterioles from the [[renal circulation]] enter and leave the glomerulus at the vascular pole. The glomerular filtrate leaves the Bowman's capsule at the renal tubule at the urinary pole.

===Glomerulus===
{{Main article|Glomerulus (kidney)|l1 = Glomerulus}}

The glomerulus is the network, known as a ''tuft'', of filtering [[capillary|capillaries]] located at the [[Renal corpuscle|vascular pole]] of the renal corpuscle in Bowman's capsule. Each glomerulus receives its blood supply from an [[afferent arterioles|afferent arteriole]] of the [[renal circulation]]. The glomerular blood pressure provides the driving force for water and solutes to be filtered out of the [[blood plasma]], and into the interior of [[Bowman's capsule]], called Bowman's space.

Only about a fifth of the plasma is filtered in the glomerulus. The rest passes into an [[efferent arteriole]]. The diameter of the efferent arteriole is smaller than that of the afferent, and this difference increases the hydrostatic pressure in the glomerulus.

===Bowman's capsule===
The [[Bowman's capsule]], also called the glomerular capsule, surrounds the glomerulus. It is composed of a visceral inner layer formed by specialized cells called [[podocyte]]s, and a parietal outer layer composed of [[simple squamous epithelium]]. Fluids from [[blood]] in the glomerulus are ultrafiltered through several layers, resulting in what is known as the filtrate.

The filtrate next moves to the renal tubule, where it is further processed to form [[urine]]. The different stages of this fluid are collectively known as the [[tubular fluid]].

===Renal tubule=== <!--Renal tubule redirects here-->
The renal tubule is a continuous and long pipe-like structure containing the [[tubular fluid]] filtered through the glomerulus.<ref>{{cite web | work = Ecology & Evolutionary Biology - University of Colorado at Boulder. | title = The Kidney Tubule I: Urine Production. | url = http://www.colorado.edu/eeb/web_resources/cartoons/nephrex1.html | access-date = March 6, 2007 | archive-url = https://web.archive.org/web/20071002180140/http://www.colorado.edu/eeb/web_resources/cartoons/nephrex1.html | archive-date=October 2, 2007 }}</ref> The filtrate passing through the renal tubule ultimately ends at the [[collecting duct system]].<ref>{{cite book| vauthors = Hook JB, Goldstein RS |title=Toxicology of the Kidney|publisher=Raven Press|year=1993|isbn=0-88167-885-6 |page=8 |url =https://books.google.com/books?id=61CAfmFDBrEC}}</ref>

The components of the renal tubule are:

# [[Proximal convoluted tubule]]: lies in the cortex and is lined by 'simple cuboidal epithelium with [[brush border]]s' which greatly increase surface area for absorption.
# [[Loop of Henle]]: lies in the medulla and is U-shaped (similar to a hair-pin)
#* [[Descending limb of loop of Henle]]: one segment of equal thickness
#* [[Ascending limb of loop of Henle]]: two segments of differing thickness (proximal portion lined by simple squamous epithelium is called the [[thin ascending limb of loop of Henle]], distal portion lined by simple cuboidal epithelium is called the [[thick ascending limb of loop of Henle]]).
# [[Distal convoluted tubule]]: lies in the cortex 
# [[Collecting tubule]]

The epithelial cells that form these nephron segments can be distinguished by the shapes of their actin cytoskeleton visualized by confocal microscopy of fluorescent phalloidin.<ref>{{cite journal |vauthors=Kumaran GK, Hanukoglu I |title=Identification and classification of epithelial cells in nephron segments by actin cytoskeleton patterns |journal=FEBS J |volume=287 |issue=6 |pages=1176–1194 |date=March 2020 |pmid=31605441 |pmc=7384063 |doi=10.1111/febs.15088 |url=https://febs.onlinelibrary.wiley.com/doi/10.1111/febs.15088}}</ref>

Blood from the efferent arteriole, containing everything that was not filtered out in the glomerulus, moves into the [[peritubular capillaries]], tiny blood vessels that surround the loop of Henle and the proximal and distal tubules, where the tubular fluid flows. Substances then reabsorb from the latter back to the blood stream.

The peritubular capillaries then recombine to form an efferent venule, which combines with efferent venules from other nephrons into the renal vein, and rejoins the main bloodstream.

=== Difference in Length of Nephrons===
'''Cortical nephrons''' (the majority of nephrons) start high in the cortex and have a short loop of Henle which does not penetrate deeply into the medulla. Cortical nephrons can be subdivided into ''superficial cortical nephrons'' and ''midcortical nephrons''.<ref>{{cite book| title= Essentials of Human Physiology| vauthors = Nosek TM | chapter=Section 7/7ch03/7ch03p16 |chapter-url=http://humanphysiology.tuars.com/program/section7/7ch03/7ch03p16.htm |archive-url=https://web.archive.org/web/20160324124828/http://humanphysiology.tuars.com/program/section7/7ch03/7ch03p16.htm|archive-date=2016-03-24}}</ref>

{{anchor|Juxtamedullary nephron}}
'''Juxtamedullary nephrons'''{{explain|reason=Juxtamedullary nephron redirects here, and nothing says what it is|date=August 2022}} start low in the cortex near the medulla and have a long loop of Henle which penetrates deeply into the renal medulla: only they have their loop of Henle surrounded by the [[Straight arterioles of kidney|vasa recta]]. These long loops of Henle and their associated vasa recta create a hyperosmolar gradient that allows for the generation of concentrated [[urine]].<ref>{{cite book | vauthors = Jameson JL, Loscalzo J |title=Harrison's Nephrology and Acid-Base Disorders|publisher=McGraw-Hill Professional|year=2010|isbn=978-0-07-166339-7|page=3|url=https://books.google.com/books?id=yoeXSV8O2wUC&pg=PA3}}</ref> Also the hairpin bend penetrates up to the inner zone of medulla.<ref>{{cite web|title=Regulation of Urine Concentration |url=http://www.cliffsnotes.com/study_guide/Regulation-of-Urine-Concentration.topicArticleId-277792,articleId-277776.html |work=Anatomy & Physiology |publisher=CliffsNotes |access-date=27 November 2012 |url-status=dead |archive-url=https://web.archive.org/web/20121025033759/http://www.cliffsnotes.com/study_guide/Regulation-of-Urine-Concentration.topicArticleId-277792%2CarticleId-277776.html |archive-date=25 October 2012 }}</ref>

Juxtamedullary nephrons are found only in birds and mammals, and have a specific location: ''medullary'' refers to the [[renal medulla]], while ''juxta'' (Latin: near) refers to the relative position of the [[renal corpuscle]] of this nephron  - ''near the medulla'', but still in the cortex.  In other words, a ''juxtamedullary nephron'' is a nephron whose renal corpuscle is near the medulla, and whose [[proximal convoluted tubule]] and its associated [[loop of Henle]] occur deeper in the medulla than the other type of nephron, the [[cortical nephron]].

The juxtamedullary nephrons comprise only about 15% of the nephrons in the human kidney.<ref name="lote" />{{rp|24}} However, it is this type of nephron which is most often depicted in illustrations of nephrons.

In humans, cortical nephrons have their renal corpuscles in the outer two thirds of the cortex, whereas juxtamedullary nephrons have their corpuscles in the inner third of the cortex.<ref name="lote" />{{rp|24}}