Editing Common ostrich (section)

=====Kidney function=====

Common ostrich kidneys are fairly large and so are able to hold significant amounts of [[solutes]]. Hence, common ostriches drink relatively large volumes of water daily and [[excretion|excrete]] generous quantities of highly concentrated [[urine osmolality|urine]]. It is when drinking water is unavailable or withdrawn that the urine becomes highly concentrated with [[uric acid|uric acid and urates]].<ref name=Deeming /> It seems that common ostriches who normally drink relatively large amounts of water tend to rely on [[renal function|renal conservation]] of water within the kidney system when drinking water is scarce. Though there have been no official detailed [[renal function|renal studies]] conducted<ref>{{cite web |last=Bennett |first=Darin C. |author2=Yutaka Karasawa |title=Effect of Protein Intake on Kidney Function in Adult Female Ostriches (''Struthio Camelus'') |year=2003 |pages=vii |url=http://www.publish.csiro.au/?act=view_file&file_id=EAv48n10posters.pdf}}</ref> on the [[Hagen-Poiseuille equation|flow rate]] ([[Hagen-Poiseuille equation|Poiseuille's Law]]) and composition of the ureteral urine in the ostrich, knowledge of [[renal function]] has been based on samples of [[urine|cloacal urine]], and samples or quantitative collections of [[urine|voided urine]].<ref name=Deeming /> Studies have shown that the amount of water intake and [[dehydration]] impacts the [[plasma osmolality]] and [[urine osmolality]] within various sized ostriches. During a normal hydration state of the kidneys, young ostriches tend to have a measured plasma osmolality of 284 [[mOsm]] and urine osmolality of 62 mOsm. Adults have higher rates with a plasma osmolality of 330 mOsm and urine osmolality of 163 mOsm. The [[osmolality]] of both plasma and urine can alter in regards to whether there is an excess or depleted amount of water present within the kidneys. An interesting fact of common ostriches is that when water is freely available, the urine osmolality can reduce to 60–70 [[mOsm]], not losing any necessary solutes from the kidneys when excess water is excreted.<ref name=Deeming /> Dehydrated or salt-loaded ostriches can reach a maximal urine osmolality of approximately 800 mOsm. When the plasma osmolality has been measured simultaneously with the maximal osmotic urine, it is seen that the urine:plasma ratio is 2.6:1, the highest encountered among avian species.<ref name=Deeming /> Along with dehydration, there is also a reduction in [[Hagen-Poiseuille equation|flow rate]] from 20 L·d<sup>−1</sup> to only 0.3–0.5 L·d<sup>−1</sup>.

In mammals and common ostriches, the increase of the [[renal function|glomerular filtration rate (GFR)]] and [[urine flow rate| urine flow rate (UFR)]] is due to a high protein diets. As seen in various studies, scientists have measured [[clearance (medicine)|clearance of]] [[creatinine]], a fairly reliable marker of glomerular filtration rate (GFR).<ref name=Deeming /> It has been seen that during normal hydration within the kidneys, the glomerular filtration rate is approximately 92&nbsp;ml/min. However, when an ostrich experiences [[dehydration]] for at least 48 hours (2 days), this value diminishes to only 25% of the hydrated GFR rate. Thus in response to the dehydration, ostrich kidneys [[secretion|secrete]] small amounts of very viscous glomerular filtrates that have not been broken down and return them to the [[circulatory system]] through [[blood vessel]]s. The reduction of GFR during dehydration is extremely high and so the fractional excretion of water (urine flow rate as a percentage of GFR) drops down from 15% at normal hydration to 1% during dehydration.<ref name=Deeming />