2,232
edits
Changes
Aquaporins of the Kidney and Water Homeostasis - Anatomy & Physiology (view source)
Revision as of 20:02, 11 August 2008
, 20:02, 11 August 2008no edit summary
==Other Means of Water Homeostasis==
==Other Means of Water Homeostasis==
As well as the aquaporins in the distal tubule and collecting duct significant water reabsorption occurs in the [[Proximal Tubule - Anatomy & Physiology| proximal tubule]] and the [[Loop Of Henle - Anatomy & Physiology| Loop of Henle]] and is linked to the absorption of [[Sodium Homeostasis - Physiology| sodium.]]
As well as the aquaporins in the distal tubule and collecting duct significant water reabsorption occurs in the [[Proximal Tubule - Anatomy & Physiology| proximal tubule]] and the [[Loop Of Henle - Anatomy & Physiology| Loop of Henle]] and is linked to the absorption of [[Sodium Homeostasis - Physiology| sodium.]]
==Species Variation of the Ability to Conserve Water==
Mammals and birds can produce urine both more and less concentrated than plasma in order to conserve or excrete water. The excretion is done without interefering with the levels of solute excretion. The ability to concentrate urine depends greatly on a species access to water. Animals with access to lots of water have less of a need and therefore have not evolved great mechanisms to concentrate urine for example the beaver. However animals who have limited access to water and say live in more arrid environments such as the kangaroo rat which lives in a desert habitat have evolved very good mechanisms to reabsorb lots of water and produce a very concentrated urine.
===Nephron Species Differances===
The variation in nephron structure is pivotal to the to the species differances with regard to the ability to concentrate urine. Broadly there are two structures.
=====Juxtamedullary Nephrons=====
These nephrons have glomeruli in the cortex and loops of henle which descend into the medulla. These are the commonly described nephrons. Significant urine concentration is achieved thanks to the hyperosmolar medulla achieved via the counter current multiplier drawing water out of the collecting ducts.
=====Cortical Nephrons=====
These nephrons have glomeruli in the outer cortex and their loops of henle barely penetrate the medulla. They have very limited concentrating ability.
The length of the loop of henle is the determining factor with regard to how concentrated urine an animal can produce. In species which produce very concentrated urine almost if not all of their nephrons are juxtamedullary in type and they tend to have very long loops of henle. However animals such as beavers where dehydration is not really an issue have very short loops of henle and excrete dilute urine. One surprise is however that the kangaroo rat which can concentrate urine to the equivalent of a 20% saline solution actually has shorter nephrons than some larger species with less ability to concentrate urine. This has been attributed to it having a much higher metabolic rate and thus more active transport meaning greater gradients can occur on any given length of its loop of henle.