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Reabsorption and Secretion Along the Distal Tubule and Collecting Duct - Anatomy & Physiology (view source)
Revision as of 15:09, 3 September 2008
, 15:09, 3 September 2008no edit summary
*** ATP driven proton secretion
*** ATP driven proton secretion
==Juxtaglomerular Apparatus==
===Juxtaglomerular Apparatus===
[[Image:juxtaapp.jpg|right|thumb|200px|<small><center>Histology section showing the juxtaglomerular apparatus (© RVC 2008)</center></small>]]
[[Image:juxtaapp.jpg|right|thumb|200px|<small><center>Histology section showing the juxtaglomerular apparatus (© RVC 2008)</center></small>]]
* The terminal portion of the straight distal tubule contacts the afferent and efferent vessels supplying its own glomerulus
* The terminal portion of the straight distal tubule contacts the afferent and efferent vessels supplying its own glomerulus
** The Extraglomerular Mesangium has an unclear function
** The Extraglomerular Mesangium has an unclear function
==Developmental==
===Developmental===
Develops from metanephric tubule
Develops from metanephric tubule
[[Image:collductloh.jpg|right|thumb|250px|<small><center>Histology section of the collecting duct showing the close proximity of the loop of henle (© RVC 2008)</center></small>]]
==Collecting Duct==
This part of the nephron has two cell types
===Principal Cells===
[[Image:collductexch.jpg|right|thumb|250px|<small><center>Exchange in the Principal Cells of the Collecting Duct</center></small>]]
* [[Endocrine System - Pituitary Gland - Anatomy & Physiology #Posterior Pituitary Gland | ADH]] acts on these cells inserting [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#What are Aquaporins|aquaporins]] into the cell membranes
* It is released from the [[Endocrine System - Pituitary Gland - Anatomy & Physiology #Posterior Pituitary Gland | posterior pituitary gland]]
===Intercalated cells===
* The intercalated cells can be subdivided further to:
** Alpha intercalated cells secrete H<sup>+</sup>
** Beta intercalated cells secrete HCO<sub>3</sub><sup>-</sup>
===Developmental===
* Develops from branched ureteric bud
===The Concentrating Mechanism, Aquaporins and ADH===
Water is drawn from the lumen of the tubule by the increasing hypertonicity of the surrounding tissue as the duct makes its way deeper into the medulla. However this reabsorption is only possible thanks to [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology|ADH]] inserting [[Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology#What are Aquaporins|aquaporins]] into the apical membrane. These channels are always present on the basolateral membrane of the epithelial cells but not on the apical membrane. The reabsorption would not be possible if the urine did not go back up the [[Loop Of Henle - Anatomy & Physiology #Thick ascending limb| thick ascending limb]] of the loop of henle, where its concentration was decreased by the reabsorption of salt, but instead went straight into the collecting ducts. Although this would mean very concentrated urine it would result in massive salt losses. Thus the collecting duct allows for very concentrated urine with minimal salt loss. It also allows the concentration of the urine to vary from dilute to concentrated under the control of the hypothalamus and ADH concentrations.