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| <br> | | <br> |
| + | ==The Ability of the Kidney To Alter the Water Content of the Body== |
| + | |
| + | * Take a dog which weighs 20kg and is drinking normally. It will produce 0.5l of water per 24 hours. |
| + | * If the dog drinks excessively it can produce 8ml urine/min to compensate meaning a total of 11 litres per 24 hours |
| + | * If a dog is denied water the production drops to a tiny 0.15 litres per 24 hours |
| + | |
| + | |
| + | The reabsorption of water can occur paracellulary - the main method in the proximal tubule or transcellulary - the main method in the distal tubule and collecting duct. |
| + | * Contrary to popular belief diffusion of water accross lipid bilayers (transcellulary) is too slow for most physiological processes |
| + | * Aquaporins solve this problem |
| + | |
| ==What are Aquaporins== | | ==What are Aquaporins== |
| * Family of membrane channel proteins | | * Family of membrane channel proteins |
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| ** Thanks to the gradient created by the hypertonic medulla which is present due to the countercurrent multiplier in the [[Loop Of Henle - Anatomy & Physiology| Loop of Henle]] | | ** Thanks to the gradient created by the hypertonic medulla which is present due to the countercurrent multiplier in the [[Loop Of Henle - Anatomy & Physiology| Loop of Henle]] |
| * This system allows both concentrated and dilute urine to be produced depending on ADH secretion and therefore the density of aquaporins in the principal cell membranes | | * This system allows both concentrated and dilute urine to be produced depending on ADH secretion and therefore the density of aquaporins in the principal cell membranes |
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− | ==Why Do We Need Aquaporins==
| |
− | * Contrary to popular belief diffusion of water accross lipid bilayers is too slow for most physiological processes
| |
− | * Aquaporins solve this problem
| |
| | | |
| ==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.]] |