Editing Loop of Henle (section)

==Importance of loop of Henle length==

While the physical shape of the loop of Henle is vital to the creation and maintenance of the medullary gradient, the length imposes a limit to the gradient. In other words, the length of the loop of Henle limits the concentration of the gradient, i.e., the longer the loop, the greater the osmotic gradient. Thus, longer loops would allow for steeper gradients and greater capacity to concentrate urine. Through the [[countercurrent multiplier]] the loop of Henle increases the osmolarity of the medulla. 

The loop of Henle is always a U-shaped tubule, with a descending limb and an ascending limb, however its length varies among different vertebrates. This is associated with the fact that it has two functions; whilst the first is to clean wastes, the second is to maintain a balance between ions and H<sub>2</sub>O. This allows to balance the blood pressure, blood pH and [[Membrane potential|membrane potentials]]. To achieve such balance between water and ions, the loop of Henle coordinates its function with the collecting duct to regulate the amount of water to reabsorb or to excrete. While the loop of Henle makes the medulla of the kidney salty, the collecting duct regulates the permeability of water that could be reabsorbed to such salty environment. The saltier the medulla, the more water can be reabsorbed from the pre-urine in collecting duct; before it becomes urine. <ref>Britannica, T. Editors of Encyclopaedia (2022, January 8). loop of Henle. Encyclopedia Britannica. https://www.britannica.com/science/loop-of-Henle
 </ref> [[Aquaporin-2]] (AQ2) sits in collecting duct and is selectively inserted into cell membranes, according to the body's needs, to reabsorb water to create that balance.<ref>{{cite web|url=https://medlineplus.gov/genetics/gene/aqp2/|title=AQP2 gene|website=MedlinePlus|date=1 April 2010|access-date=23 May 2023|publisher=National Library of Medicine}}</ref>

Vertebrates who live in the desert do not have access to lots of water. Therefore, some of them have a longer loop of Henle which creates a saltier medulla, leading them to reabsorb more water from the pre-urine. For example, the urine concentration in humans can be as concentrated as 1400 mOsm which is limited by the length of our loop of Henle, i.e., 2.2 mm. While a camel's loop of Henle, which is around 4.1 mm, can reach 2800 mOsm. Another example is the Australian mouse whose loop of Henle, 5.2 mm, can make the medulla as salty as 9000 mOsm.<ref> https://www.open.edu/openlearn/nature-environment/natural-history/animals-the-extremes-the-desert-environment/content-section-3.2/</ref> This permits that the urine of these rodents can reach 9000 mOsm, in other words, a highly concentrated urine.