Editing Common ostrich (section)

==Physiology==
===Respiration===
====Anatomy====
[[File:Ostrich Respiratory Anatomy.svg|thumb|Diagrammatic location of the air sacs]]
 
Morphology of the common ostrich [[lung]] indicates that the structure conforms to that of the other [[bird anatomy|avian species]], but still retains parts of its primitive [[ratite]] structure.<ref name=Makanya /> The opening to the respiratory pathway begins with the [[larynx|laryngeal]] cavity lying posterior to the [[posterior nasal apertures|choanae]] within the [[Mouth|buccal cavity]].<ref name=Deeming /> The tip of the tongue then lies [[anatomical terms of location|anterior]] to the choanae, excluding the nasal respiratory pathway from the buccal cavity.<ref name=Deeming /> The trachea lies [[Anatomical terms of location|ventrally]] to the cervical vertebrae extending from the [[larynx]] to the [[Syrinx (bird anatomy)|syrinx]], where the trachea enters the [[thorax]], dividing into two primary [[bronchus|bronchi]], one to each lung, in which they continue directly through to become mesobronchi.<ref name=Deeming /> Ten different air sacs attach to the lungs to form areas for respiration.<ref name=Deeming /> The most [[Anatomical terms of location|posterior]] [[air sacs]] (abdominal and post-thoracic) differ in that the right abdominal air sac is relatively small, lying to the right of the [[mesentery]], and [[Anatomical terms of location|dorsally]] to the liver.<ref name=Deeming /> While the left abdominal air sac is large and lies to the left of the mesentery.<ref name=Deeming /> The connection from the main mesobronchi to the more [[Anatomical terms of location|anterior]] air sacs including the [[clavicle|interclavicular]], lateral clavicular, and pre-thoracic sacs known as the ventrobronchi region. While the [[Anatomical terms of location|caudal]] end of the mesobronchus branches into several dorsobronchi. Together, the ventrobronchi and dorsobronchi are connected by intra-pulmonary airways, the [[bird anatomy|parabronchi]], which form an arcade structure within the lung called the paleopulmo. It is the only structure found in primitive birds such as ratites.<ref name=Deeming />
[[File:Struthio_syrinx.jpg|thumb|The syrinx has simple muscles. The only sounds that can be produced are roars and hisses.]]
The largest air sacs found within the respiratory system are those of the post-thoracic region, while the others decrease in size respectively, the interclavicular (unpaired), abdominal, pre-thoracic, and lateral clavicular sacs.<ref name=Schmidt-Nielsen /> The adult common ostrich lung lacks connective tissue known as interparabronchial septa, which render strength to the non-compliant avian lung in other bird species. Due to this the lack of connective tissue surrounding the parabronchi and adjacent parabronchial lumen, they exchange blood capillaries or [[blood vessel|avascular]] epithelial plates.<ref name=Makanya /> Like mammals, ostrich lungs contain an abundance of type II cells at gas exchange sites; an adaptation for preventing lung collapse during slight volume changes.<ref name=Makanya />

====Function====
The common ostrich is an [[endotherm]] and maintains a body temperature of {{cvt|38.1|-|39.7|C}} in its extreme living temperature conditions, such as the heat of the savanna and desert regions of Africa.<ref name=King/> The ostrich utilizes its respiratory system via a costal pump for ventilation rather than a [[thoracic diaphragm|diaphragmatic pump]] as seen in most mammals.<ref name=Deeming/> Thus, they are able to use a series of air sacs connected to the [[bird anatomy|lungs]]. The use of air sacs forms the basis for the three main avian respiratory characteristics:
# Air is able to flow continuously in one direction through the lung, making it more efficient than the mammalian lung. 
# It provides birds with a large residual volume, allowing them to breathe much more slowly and deeply than a mammal of the same body mass. 
# It provides a large source of air that is used not only for gaseous exchange, but also for the transfer of heat by evaporation.<ref name=Deeming/>

[[File:Struthio camelus portrait Whipsnade Zoo.jpg|frameless|right|alt=Ostrich portrait showing its large eyes and long eyelashes, its flat, broad beak, and its nostrils]]

Inhalation begins at the mouth and the nostrils located at the front of the beak. The air then flows through the anatomical dead space of a highly vascular trachea ({{circa}} {{cvt|78|cm}}) and expansive bronchial system, where it is further conducted to the posterior air sacs.<ref name=zool241/> Air flow through the [[bird anatomy|parabronchi]] of the paleopulmo is in the same direction to the dorsobronchi during inspiration and expiration. Inspired air moves into the respiratory system as a result of the expansion of thoraco abdominal cavity; controlled by [[bird anatomy|inspiratory muscles]]. During expiration, oxygen poor air flows to the anterior air sacs<ref name=Schmidt-Nielsen/> and is expelled by the action of the [[bird anatomy|expiratory muscles]]. The common ostrich air sacs play a key role in respiration, since they are capacious, and increase surface area (as described by the [[Fick Principle]]).<ref name=zool241/> The oxygen rich air flows [[wikt:unidirectional|unidirectionally]] across the respiratory surface of the lungs; providing the blood that has a crosscurrent flow with a high concentration of oxygen.<ref name=zool241/>

To compensate for the large "dead" space, the common ostrich trachea lacks valves to allow faster inspiratory air flow.<ref name=MainaSingh/> In addition, the [[lung volumes|total lung capacity]] of the respiratory system, (including the lungs and ten air sacs) of a {{cvt|100|kg}} ostrich is about {{cvt|15|L|cuin}}, with a [[tidal volume]] ranging from {{cvt|1.2|-|1.5|L|cuin}}.<ref name=Schmidt-Nielsen/><ref name=MainaSingh>{{Cite journal 
| last1 = Maina | first1 = J.N. 
| last2 = Singh | first2 = P. 
| last3 = Moss  | first3 = E.A. 
| doi = 10.1016/j.resp.2009.09.011 
| title = Inspiratory aerodynamic valving occurs in the ostrich, ''Struthio camelus'', lung: A computational fluid dynamics study under resting unsteady state inhalation 
| journal = Respiratory Physiology & Neurobiology 
| volume = 169 
| issue = 3 
| pages = 262–270 
| year = 2009 
| pmid = 19786124 
| s2cid = 70939 
}}</ref> The tidal volume is seen to double resulting in a 16-fold increase in ventilation.<ref name=Deeming/> Overall, ostrich respiration can be thought of as a high velocity-low pressure system.<ref name=Schmidt-Nielsen/> At rest, there is a small pressure difference between the ostrich air sacs and the atmosphere, suggesting simultaneous filling and emptying of the air sacs.<ref name=MainaSingh/>

The increase in respiration rate from the low range to the high range is sudden and occurs in response to [[hyperthermia]]. Birds lack sweat glands, so when placed under stress due to heat, they heavily rely upon increased evaporation from the respiratory system for heat transfer. This rise in [[respiration rate]] however is not necessarily associated with a greater rate of oxygen consumption.<ref name=Deeming/> Therefore, unlike most other birds, the common ostrich is able to dissipate heat through panting without experiencing [[respiratory alkalosis]] by modifying ventilation of the respiratory medium. During [[hyperpnea]] ostriches pant at a respiratory rate of 40–60&nbsp;cycles per minute, versus their resting rate of 6–12&nbsp;cycles per minute.<ref name=Schmidt-Nielsen/> Hot, dry, and moisture lacking properties of the common ostrich respiratory medium affect oxygen's diffusion rate ([[Henry's Law]]).<ref name=zool241>{{cite book |last1=Hill |first1=W.R. |last2=Wyse |first2=A.G. |last3=Anderson |first3=M. |name-list-style=amp |year=2012 |title=Animal Physiology |edition=3rd |publisher=Sinauer Associates |place=Sunderland, MA}}{{page needed|date=November 2013}}</ref>

Common ostriches develop via [[Angiogenesis|Intussusceptive angiogenesis]], a mechanism of [[blood vessel]] formation, characterizing many organs.<ref name=Makanya/> It is not only involved in vasculature expansion, but also in angioadaptation<ref>{{cite journal |pmid=12270956 |year=2002 |last1=Zakrzewicz |first1=A. |last2=Secomb |first2=T.W. |last3=Pries |first3=A.R. |title=Angioadaptation: Keeping the vascular system in shape |volume=17 |issue=5 |pages=197–201 |journal=News in Physiological Sciences |doi=10.1152/nips.01395.2001 }}</ref> of vessels to meet physiological requirements.<ref name=Makanya /> The use of such mechanisms demonstrates an increase in the later stages of [[lung]] development, along with elaborate parabronchial [[vasculature]], and reorientation of the [[gas exchange]] blood capillaries to establish the crosscurrent system at the blood-gas barrier.<ref name=Makanya/> The [[blood-air barrier|blood–gas barrier]] (BGB) of their lung tissue is thick. The advantage of this thick barrier may be protection from damage by large volumes of blood flow in times of activity, such as running,<ref name=Maina/> since air is pumped by the air sacs rather than the lung itself. As a result, the [[capillaries]] in the parabronchi have thinner walls, permitting more efficient gaseous exchange.<ref name=Deeming/> In combination with separate pulmonary and systemic circulatory systems, it helps to reduce stress on the BGB.<ref name=Makanya/>

===Circulation===

====Heart anatomy====

The common ostrich heart is a closed system, contractile chamber. It is composed of [[myogenic]] muscular tissue associated with heart contraction features. There is a double circulatory plan in place possessing both a [[pulmonary circuit]] and systemic circuit.<ref name=zool241 />

The common ostrich's heart has similar features to other avian species, like having a [[Cone|conically]] shaped heart and being enclosed by a [[Fibrous pericardium|pericardium]] layer.<ref name=heartanatomy>{{cite journal|author=Tadjalli, M.|author2=Ghazi, S. R.|author3=Parto, P.|name-list-style=amp|url=http://ijvr.shirazu.ac.ir/article_1084_16026a1de1a104067949c765dc03ca9f.pdf|year=2009|title=Gross anatomy of the heart in Ostrich (''Struthio camelus'')|journal=Iran J. Vet. Res.|volume=10|issue=1|pages=21–7|access-date=17 March 2017|archive-date=18 March 2017|archive-url=https://web.archive.org/web/20170318004059/http://ijvr.shirazu.ac.ir/article_1084_16026a1de1a104067949c765dc03ca9f.pdf|url-status=dead}}</ref> Moreover, similarities also include a larger [[right atrium]] volume and a thicker [[left ventricle]] to fulfil the [[Circulatory system|systemic circuit]].<ref name=heartanatomy /> The ostrich heart has three features that are absent in related birds: 
# The right [[Heart valve|atrioventricular valve]] is fixed to the [[interventricular septum]], by a thick muscular stock, which prevents back-flow of blood into the atrium when [[Cardiac cycle|ventricular systole]] is occurring.<ref name=heartanatomy /> In the [[fowl]] this valve is only connected by a short septal attachment.<ref name=heartanatomy /> 
# [[Pulmonary vein]]s attach to the left atrium separately, and also the opening to the pulmonary veins are separated by a septum.<ref name=heartanatomy /> 
# [[Septomarginal trabecula|Moderator bands]], full of [[Purkinje fibers]], are found in different locations in the left and right ventricles.<ref name=heartanatomy /> These bands are associated with contractions of the heart and suggests this difference causes the left ventricle to contract harder to create more pressure for a completed circulation of blood around the body.<ref name=heartanatomy />

The [[atrioventricular node]] position differs from other fowl. It is located in the [[endocardium]] of the atrial surface of the right atrioventricular valve. It is not covered by connective tissue, which is characteristic of vertebrate heart anatomy. It also contains fewer [[myofibrils]] than usual myocardial cells. The AV node connects the atrial and ventricular chambers. It functions to carry the electrical impulse from the atria to the ventricle. Upon view, the myocardial cells are observed to have large densely packed chromosomes within the nucleus.<ref name =Parto/>

The [[Coronary circulation|coronary]] [[arteries]] start in the right and left aortic sinus and provide blood to the heart muscle in a similar fashion to most other vertebrates.<ref name =Henriquez/> Other domestic birds capable of flight have three or more [[Coronary circulation|coronary]] arteries that supply blood to the heart muscle. The blood supply by the coronary arteries are fashioned starting as a large branch over the surface of the heart. It then moves along the [[coronary groove]] and continues on into the tissue as [[Ventricle (heart)|interventricular]] branches toward the [[apex of the heart]]. The [[atrium (heart)|atria]], [[ventricle (heart)|ventricle]]s, and [[septum]] are supplied of blood by this modality. The deep branches of the coronary arteries found within the heart tissue are small and supply the interventricular and right [[atrioventricular node|atrioventricular]] valve with blood nutrients for which to carry out their processes. The interatrial artery of the ostrich is small in size and exclusively supplies blood to only part of the left auricle and interatrial [[septum]].<ref name =Bezuidenhout/><ref name =Bezuidenhout2/>

These [[Purkinje fibers]] (p-fibers) found in the hearts moderator bands are a specialized cardiac muscle fiber that causes the heart to contract.<ref name=purkinje>{{cite journal|author=Parto, P.|author2=Tadjalli, M.|author3=Ghazi, S. R.|author4=Salamat, M. A.|name-list-style=amp|year=2013|title=Distribution and Structure of Purkinje Fibers in the Heart of Ostrich (''Struthio camelus'') with the Special References on the Ultrastructure|journal= International Journal of Zoology|doi=10.1155/2013/293643|volume=2013|pages=1–6|doi-access=free}}</ref> The Purkinje cells are mostly found within both the endocardium and the sub-endocardium.<ref name=purkinje /> The [[sinoatrial node]] shows a small concentration of Purkinje fibers, however, continuing through the [[Electrical conduction system of the heart|conducting pathway]] of the heart the [[bundle of his]] shows the highest amount of these Purkinje fibers.<ref name=purkinje />

====Blood composition====

The [[red blood cell]] count per unit volume in the ostrich is about 40% of that of a human; however, the red blood cells of the ostrich are about three times larger than the red blood cells of a human.<ref name=metabolism1>{{Cite journal | last1 = Isaacks | first1 = R. | last2 = Harkness | first2 = D. | last3 = Sampsell | first3 = J. | last4 = Adler | first4 = S. | last5 = Roth | first5 = C. | last6 = Kim | first6 = P. | last7 = Goldman | first7 = R. | doi = 10.1111/j.1432-1033.1977.tb11700.x | title = Studies on Avian Erythrocyte Metabolism. Inositol Tetrakisphosphate: The Major Phosphate Compound in the Erythrocytes of the Ostrich (Struthio camelus camelus) | journal = European Journal of Biochemistry | volume = 77 | issue = 3 | pages = 567–574 | year = 1977 | pmid =  19258| doi-access = free }}</ref> The blood oxygen affinity, known as [[P50 (pressure)|P<sub>50</sub>]], is higher than that of both humans and similar avian species.<ref name=metabolism1 /> The reason for this decreased [[Oxygen–haemoglobin dissociation curve|oxygen affinity]] is due to the hemoglobin configuration found in common ostrich blood.<ref name=metabolism1 /> The common ostrich's [[tetramer]] is composed of [[hemoglobin]] type A and D, compared to typical mammalian tetramers composed of hemoglobin type A and B; hemoglobin D configuration causes a decreased oxygen affinity at the site of the respiratory surface.<ref name=metabolism1 />

During the [[embryo]]nic stage, [[Hemoglobin E]] is present.<ref name=metabolism2>{{Cite journal 
| doi = 10.1016/S0300-9629(76)80046-1 
| last1 = Isaacks | first1 = R. E. 
| last2 = Harkness | first2 = D. R. 
| last3 = Froeman | first3 = G. A. 
| last4 = Goldman | first4 = P. H. 
| last5 = Adler | first5 = J. L. 
| last6 = Sussman | first6 = S. A. 
| last7 = Roth | first7 = S. 
| title = Studies on avian erythrocyte metabolism—II. Relationship between the major phosphorylated metabolic intermediates and oxygen affinity of whole blood in chick embryos and chicks 
| journal = Comparative Biochemistry and Physiology A 
| volume = 53 
| issue = 2 
| pages = 151–156 
| year = 1976 
| pmid = 2411
}}</ref> This subtype increases oxygen affinity in order to transport oxygen across the allantoic membrane of the embryo.<ref name=metabolism2 /> This can be attributed to the high metabolic need of the developing embryo, thus high oxygen affinity serves to satisfy this demand. When the chick hatches hemoglobin E diminishes while hemoglobin A and D increase in concentration.<ref name=metabolism2 /> This shift in hemoglobin concentration results in both decreased oxygen affinity and increased P<sub>50</sub> value.<ref name=metabolism2 />

Furthermore, the P<sub>50</sub> value is influenced by differing organic modulators.<ref name=metabolism2 /> In the typical mammalian RBC 2,3 – DPG causes a lower affinity for oxygen. 2,3- DPG constitutes approximately 42–47%, of the cells phosphate of the embryonic ostrich.<ref name=metabolism2 /> However, the adult ostrich have no traceable 2,3- DPG.In place of 2,3-DPG the ostrich uses inositol [[polyphosphate]]s (IPP), which vary from 1–6 phosphates per molecule.<ref name=metabolism2 /> In relation to the IPP, the ostrich also uses [[Adenosine triphosphate|ATP]] to lower oxygen affinity.<ref name=metabolism2 /> ATP has a consistent concentration of phosphate in the cell<ref name=metabolism2 /> {{endash}} around 31% at [[incubation period]]s and dropping to 16–20% in 36-day-old chicks.<ref name=metabolism2 /> However, IPP has low concentrations, around 4%, of total phosphate concentration in embryonic stages, but the IPP concentration jumps to 60% of total phosphate of the cell.<ref name=metabolism2 /> The majority of phosphate concentration switches from 2,3- DPG to IPP, suggesting the result of the overall low oxygen affinity is due to these varying polyphosphates.<ref name=metabolism2 />

Concerning immunological adaptation, it was discovered that wild common ostriches have a pronounced non-specific immunity defense, with blood content reflecting high values of [[lysosome]] and [[phagocyte]] cells in medium. This is in contrast to domesticated ostriches, who in captivity develop high concentration of [[immunoglobulin]] [[antibodies]] in their circulation, indicating an acquired immunological response. It is suggested that this immunological adaptability may allow this species to have a high success rate of survival in variable environmental settings.<ref name= Cooper/>

===Osmoregulation===

====Physiological challenges====
The common ostrich is a [[Xerocole|xeric]] animal, due to the fact that it lives in habitats that are both dry and hot.<ref name=zool241 /> Water is scarce in dry and hot environments, and this poses a challenge to the ostrich's water consumption. Also the ostrich is a ground bird and cannot fly to find water sources, which poses a further challenge. Because of their size, common ostriches cannot easily escape the heat of their environment; however, they dehydrate less than their small bird counterparts because of their small [[surface area to volume ratio]].<ref name=Skadhaugeetal>{{cite journal|last=Skadhauge|first=E|author2=Warüi CN |author3=Kamau JM |author4=Maloiy GM |title=Function of the lower intestine and osmoregulation in the ostrich: preliminary anatomical and physiological observations|journal=Quarterly Journal of Experimental Physiology|year=1984|volume=69|issue=4|pages=809–18|pmid=6514998 |doi=10.1113/expphysiol.1984.sp002870|doi-access=free}}</ref> Hot, arid habitats pose osmotic stress, such as [[dehydration]], which triggers the common ostrich's [[Homeostasis|homeostatic]] response to osmoregulate.

====System overview====
The common ostrich is well-adapted to hot, arid environments through specialization of [[excretory]] organs. The common ostrich has an extremely long and developed [[colon (anatomy)|colon]] {{endash}} a length of approximately {{cvt|11|-|13|m}} {{endash}} between the [http://medical-dictionary.thefreedictionary.com/coprodeum coprodeum] and the paired [[Pyloric caeca|caeca]], which are around {{cvt|80|cm}} long.<ref name=Skadhaugeetal /> A well-developed caeca is also found and, in combination with the [[rectum]], forms the [[microbial fermentation]] chambers used for [[carbohydrate]] breakdown.<ref name=Skadhaugeetal /> The [[catabolism]] of carbohydrates produces around {{cvt|0.56|g|gr}} of water that can be used internally.<ref name=zool241 /> The majority of their [[urine]] is stored in the coprodeum, and the [[feces]] are separately stored in the terminal colon.<ref name=Skadhaugeetal /> The coprodeum is located ventral to the terminal rectum and [[urodeum]] (where the [[ureters]] open).<ref name=Deeming /> Found between the terminal rectum and coprodeum is a strong sphincter.<ref name=Deeming /> The coprodeum and cloaca are the main osmoregulatory mechanisms used for the regulation and reabsorption of ions and water, or net water conservation.<ref name=Deeming /> As expected in a species inhabiting arid regions, dehydration causes a reduction in fecal water, or dry feces.<ref name=Deeming /> This reduction is believed to be caused by high levels of plasma [[aldosterone]], which leads to rectal absorption of sodium and water.<ref name=Deeming /> Also expected is the production of [[hyperosmotic]] urine; cloacal urine has been found to be 800 [[Osmole (unit)|mOsm]].<ref name=Deeming /> The U:P (urine:plasma) ratio of the common ostrich is therefore greater than one. Diffusion of water to the coprodeum (where urine is stored) from plasma across the [[epithelium]] is voided.<ref name=Deeming /> This void is believed to be caused by the thick [[mucosal]] layering of the coprodeum.<ref name=Deeming />

Common ostriches have two [[kidney]]s, which are chocolate brown in color, are granular in texture, and lie in a depression in the [[bird anatomy|pelvic cavity]] of the dorsal wall.<ref name=Shanawany /> They are covered by [[peritoneum]] and a layer of fat.<ref name=Deeming /> Each kidney is about {{cvt|300|mm}} long, {{cvt|70|mm}} wide, and divided into a [[Anatomical terms of location|cranial]], middle, and [[caudal (anatomical term)|caudal]] sections by large veins.<ref name=Deeming /> The caudal section is the largest, extending into the middle of the pelvis.<ref name=Deeming /> The [[ureters]] leave the ventral caudomedial surface and continue caudally, near the midline into the opening of the urodeum of the cloaca.<ref name=Deeming /> Although there is no bladder, a dilated pouch of ureter stores the urine until it is secreted continuously down from the [[ureter]]s to the urodeum until discharged.<ref name=Shanawany>{{cite book|last=Shanawany|first=M.M.|title=Ostrich Production Systems|year=1999|publisher=Food and Agriculture Organization of the United Nations|isbn=978-92-5-104300-4|page=32|url=https://books.google.com/books?id=BfjUW8ZVinkC&pg=PA253}}</ref>

=====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 />

=====Water intake and turnover=====

Common ostriches employ adaptive features to manage the dry heat and [[solar radiation]] in their habitat.  Ostriches will drink available water; however, they are limited in accessing water by being flightless. They are also able to harvest water through dietary means, consuming plants such as the ''[[Euphorbia heterochroma]]'' that hold up to 87% water.<ref name=Deeming />

Water mass accounts for 68% of body mass in adult common ostriches; this is down from 84% water mass in 35-day-old chicks. The differing degrees of water retention are thought to be a result of varying body fat mass.<ref name=Deeming /> In comparison to smaller birds ostriches have a lower evaporative water loss resulting from their small body surface area per unit weight.<ref name=zool241 />

When heat stress is at its maximum, common ostriches are able to recover evaporative loss by using a [[metabolic water]] mechanism to counter the loss by urine, feces, and respiratory evaporation.  An experiment to determine the primary source of water intake in the ostrich indicated that while the ostrich does employ a [[metabolic water]] production mechanism as a source of hydration, the most important source of water is food. When ostriches were restricted to the no food or water condition, the metabolic water production was only 0.5&nbsp;L·d<sup>−1</sup>, while total water lost to urine, feces, and evaporation was 2.3&nbsp;L·d<sup>−1</sup>. When the birds were given both water and food, total water gain was 8.5&nbsp;L·d<sup>−1</sup>. In the food only condition total water gain was 10.1&nbsp;L·d<sup>−1</sup>. These results show that the [[metabolic water]] mechanism is not able to sustain water loss independently and that food intake, specifically of plants with a high water content such as ''Euphorbia heterochroma'', is necessary to overcome water loss challenges in the common ostrich's arid habitat.<ref name=Deeming />

In times of water deprivation, urine [[electrolyte]] and [[osmotic concentration]] increases while urination rate decreases. Under these conditions [[urine]] [[solute]]:plasma ratio is approximately 2.5, or [[hyperosmotic]]; that is to say that the ratio of solutes to water in the plasma is shifted down whereby reducing osmotic pressure in the plasma. Water is then able to be held back from [[excretion]], keeping the ostrich hydrated, while the passed urine contains higher concentrations of solute. This mechanism exemplifies how renal function facilitates water retention during periods of dehydration stress.<ref name=zool241 /><ref name="Withers" />

=====Nasal glands=====
A number of avian species use [[Salt gland|nasal salt glands]], alongside their kidneys, to control [[Tonicity|hypertonicity]] in their [[blood plasma]].<ref name=saltglands>{{cite journal|title=Saline-Infusion-Induced Increase in Plasma osmolality Do Not Stimulate Nasal Gland Secretion in the Ostrich (''Struthio camelus'') |journal=Physiological Zoology|jstor=30163924|year=1995|volume=68|issue=1|pages=164–175|last1=Gray|first1=David A.|last2=Brown|first2=Christopher R.|doi=10.1086/physzool.68.1.30163924|s2cid=85890608}}</ref> However, the common ostrich shows no nasal glandular function in regard to this homeostatic process.<ref name=saltglands /> Even in a state of dehydration, which increases the [[Osmotic concentration|osmolality]] of the blood, nasal salt glands show no sizeable contribution of salt elimination.<ref name=saltglands /> Also, the overall mass of the glands was less than that of the duck's nasal gland.<ref name=saltglands /> The common ostrich, having a heavier body weight, should have larger, heavier nasal glands to more effectively excrete salt from a larger volume of blood, but this is not the case. These unequal proportions contribute to the assumption that the common ostrich's nasal glands do not play any role in salt excretion.

=====Biochemistry=====
The majority of the common ostrich's internal solutes are made up of [[sodium]] ions ({{chem2|Na(+)}}), [[potassium]] ions ({{chem2|K(+)}}), [[chloride]] ions ({{chem2|Cl(-)}}), total [[short-chain fatty acid]]s (SCFA), and [[acetate]].<ref name=Skadhaugeetal /> The caecum contains a high water concentration with reduced levels nearing the terminal colon and exhibits a rapid fall in {{chem2|Na(+)}} concentrations and small changes in {{chem2|K(+)}} and {{chem2|Cl(-)}}.<ref name=Skadhaugeetal /> 
The colon is divided into three sections and takes part in solute absorption. The upper colon largely absorbs {{chem2|Na(+)}} and SCFA and partially absorbs KCl.<ref name=Skadhaugeetal /> The middle colon absorbs {{chem2|Na(+)}} and SCFA, with little net transfer of K<sup>+</sup> and Cl<sup>−</sup>.<ref name=Skadhaugeetal /> The lower colon then slightly absorbs {{chem2|Na(+)}} and water and secretes {{chem2|K(+)}}. There is no net movements of {{chem2|Cl(-)}} and SCFA found in the lower colon.<ref name=Skadhaugeetal />

When the common ostrich is in a dehydrated state, plasma osmolality, {{chem2|Na(+)}}, {{chem2|K(+)}}, and {{chem2|Cl(-)}} ions all increase; however, {{chem2|K(+)}} ions return to controlled concentration.<ref name=hormones>{{cite journal |doi=10.1016/0300-9629(88)91088-2 |title=Plasma arginine vasotocin and angiotensin II in the water deprived common ostrich (''Struthio camelus'') |year=1988 |last1=Gray |first1=D.A. |last2=Naudé |first2=R.J. |last3=Erasmus |first3=T. |journal=Comparative Biochemistry and Physiology A |volume=89 |issue=2 |pages=251–256}}</ref> The common ostrich also experiences an increase in [[haematocrit]], resulting in a [[Hypovolemia|hypovolemic state]].<ref name=hormones /> Two antidiuretic hormones, [[Vasopressin|Arginine vasotocin (AVT)]] and [[angiotensin]] (AII), are increased in blood plasma as a response to [[hyperosmolality]] and [[hypovolemia]].<ref name=hormones /> AVT triggers [[Vasopressin|antidiuretic hormone]] (ADH) which targets the [[nephrons]] of the kidney.<ref name=zool241 /> ADH causes a reabsorption of water from the lumen of the [[nephron]] to the [[extracellular fluid]] osmotically.<ref name=zool241 /> These extracellular fluids then drain into blood vessels, causing a rehydrating effect.<ref name=zool241 /> This drainage prevents loss of water by both lowering volume and increasing concentration of the urine.<ref name=zool241 /> Angiotensin, on the other hand, causes [[vasoconstriction]] on the systemic arterioles and acts as a [[dipsogen]] for ostriches.<ref name=zool241 /> Both of these antidiuretic hormones work together to maintain water levels in the body that would normally be lost due to the osmotic stress of the arid environment.

Ostriches are [[uricotelic]], excreting nitrogen in the form of [[uric acid]] and related derivatives.<ref name=zool241 /> Uric acid's low solubility in water gives a semi-solid paste consistency to the ostrich's nitrogenous waste.<ref name=zool241 />

===Thermoregulation===

Common ostriches are [[Homeothermy|homeothermic]] [[endotherm]]s; they regulate a constant body temperature via regulating their metabolic heat rate.<ref name=zool241 /> They closely regulate their core body temperature, but their [[appendage]]s may be cooler in comparison as found with regulating species.<ref name=zool241 /> The temperature of their beak, neck surfaces, lower legs, feet, and toes are regulated through heat exchange with the environment.<ref name=polly /> Up to 40% of their produced [[Warm-blooded|metabolic heat]] is [[Dissipation|dissipated]] across these structures, which account for about 12% of their total surface area.<ref name=polly>{{cite journal|author1=Polly K.|author2=Phillips |author3=Sanborn Allen F. |name-list-style=amp |doi=10.1016/0306-4565(94)90042-6|title=An infrared, thermographic study of surface temperature in three ratites: Ostrich, emu and double-wattled cassowary|year=1994|journal=Journal of Thermal Biology|volume=19|issue=6|pages=423–430 |bibcode=1994JTBio..19..423P }}</ref> Total evaporative water loss (TEWL) is statistically lower in the common ostrich than in membering ratites.<ref name=Mitchell />

As ambient temperature increases, dry heat loss decreases, but evaporative heat loss increases because of increased [[Respiration (physiology)|respiration]].<ref name=polly /> As ostriches experience high ambient temperatures, circa {{cvt|50|C}}, they become slightly hyperthermic; however, they can maintain a stable body temperature, around {{cvt|40|C}}, for up to 8 hours in these conditions.<ref name=Schmidt-Nielsen/> When dehydrated, the common ostrich minimizes water loss, causing the body temperature to increase further.<ref name=Schmidt-Nielsen/> When the body heat is allowed to increase the [[temperature gradient]] between the common ostrich and ambient heat is [[Thermodynamic equilibrium|equilibrated]].<ref name=zool241 />

====Physical adaptations====

Common ostriches have developed a comprehensive set of behavioral adaptations for [[thermoregulation]], such as altering their feathers.<ref name=Deeming /> Common ostriches display a feather fluffing behavior that aids them in thermoregulation by regulating [[Convection (heat transfer)|convective heat loss]] at high ambient temperatures.<ref name=polly /> They may also physically seek out shade in times of high ambient temperatures. When feather fluffing, they contract their muscles to raise their feathers to increase the air space next to their skin.<ref name=zool241 /> This air space provides an insulating thickness of {{cvt|7|cm}}.<ref>Mitchell</ref> The ostrich will also expose the thermal windows of their unfeathered skin to enhance convective and radiative loss in times of heat stress.<ref name=Mitchell>{{cite journal|last=Mitchell|first=Malcolm|title=Ostrich Welfare and Transport|journal=Ostrich Welfare|series=Ratite Science Newsletter|pages=1–4|url=http://www.worldpoultry.net/PageFiles/28775/001_boerderij-download-WP6727D01.pdf|access-date=28 December 2013|archive-date=28 December 2013|archive-url=https://web.archive.org/web/20131228103741/http://www.worldpoultry.net/PageFiles/28775/001_boerderij-download-WP6727D01.pdf|url-status=dead}}</ref> At higher ambient temperatures lower appendage temperature increases to {{cvt|5|C-change}} difference from ambient temperature.<ref name=polly /> Neck surfaces are around {{cvt|6|-|7|C-change}} difference at most ambient temperatures, except when temperatures are around {{cvt|25|C}} it was only {{cvt|4|C-change}} above ambient.<ref name=polly />

At low ambient temperatures the common ostrich utilizes feather flattening, which conserves body heat through insulation. The low [[Thermal conduction|conductance coefficient]] of air allows less heat to be lost to the environment.<ref name=zool241 /> This flattening behavior compensate for common ostrich's rather poor cutaneous evaporative water loss (CEWL).<ref name=Louw>{{cite journal|last=Louw|first=Gideon|author2=Belonje, Coetzee|title=Renal Function, Respiration, Heart Rate and Thermoregulation in the Ostrich (''Struthio Camelus'')|journal=Scient. Pap. Namib Desert Res. STN|year=1969|volume=42|pages=43–54|url=http://www.the-eis.com/data/literature/Louw_1969_sci_pap_NDRS_ostrich.pdf|access-date=29 November 2013}}</ref> These feather-heavy areas such as the body, thighs, and wings do not usually vary much from ambient temperatures due to this behavioural controls.<ref name=polly /> This ostrich will also cover its legs to reduce heat loss to the environment, along with undergoing [[piloerection]] and [[shiver]]ing when faced with low ambient temperatures.

====Internal adaptations====
The use of [[Countercurrent exchange|countercurrent]] heat exchange with blood flow allows for regulated conservation/ elimination of heat of appendages.<ref name=zool241/> When ambient temperatures are low, [[Heterothermy|heterotherms]] will constrict their arterioles to reduce heat loss along skin surfaces.<ref name=zool241/> The reverse occurs at high ambient temperatures, arterioles [[Vasodilation|dilate]] to increase heat loss.<ref name=zool241/>
 
At [[Room temperature|ambient temperatures]] below their body temperatures ([[thermal neutral zone]] (TNZ)), common ostriches decrease body surface temperatures so that heat loss occurs only across about 10% of total surface area.<ref name=polly/> This 10% include critical areas that require blood flow to remain high to prevent freezing, such as their eyes.<ref name=polly/> Their eyes and ears tend to be the warmest regions.<ref name=polly/> It has been found that temperatures of lower appendages were no more than {{cvt|2.5|C-change}} above ambient temperature, which minimizes heat exchange between feet, toes, wings, and legs.<ref name=polly/>

Both the Gular and air sacs, being close to body temperature, are the main contributors to heat and water loss.<ref name=Schmidt-Nielsen/> Surface temperature can be affected by the rate of blood flow to a certain area and also by the surface area of the surrounding tissue.<ref name=zool241/> The ostrich reduces blood flow to the trachea to cool itself and [[Vasodilation|vasodilates]] to its blood vessels around the gular region to raise the temperature of the tissue.<ref name=Schmidt-Nielsen/> The air sacs are poorly vascularized but show an increased temperature, which aids in heat loss.<ref name=Schmidt-Nielsen/>

Common ostriches have evolved a 'selective brain cooling' mechanism as a means of thermoregulation. This modality allows the common ostrich to manage the temperature of the blood going to the brain in response to the extreme [[ambient temperature]] of the surroundings. The morphology for heat exchange occurs via [[cerebral arteries]] and the [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]], a network of arteries originating from the [[ophthalmic artery]]. The [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]] is [[analogous]] to the [[carotid rete]] found in mammals, as it also facilitates transfer of heat from arterial blood coming from the core to venous blood returning from the evaporative surfaces at the head.<ref name=Maloney/>

Researchers suggest that common ostriches also employ a 'selective brain warming' mechanism in response to cooler surrounding temperatures in the evenings. The brain was found to maintain a warmer temperature when compared to [[carotid]] [[arterial]] blood supply. Researchers hypothesize three mechanisms that could explain this finding:<ref name=Maloney/>
# They first suggest a possible increase in [[metabolic]] heat production within the brain tissue itself to compensate for the colder [[arterial]] blood arriving from the core.
# They also speculate that there is an overall decrease in cerebral blood flow to the brain.
# Finally, they suggest that warm venous blood [[perfusion]] at the [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]] helps to warm the cerebral blood that supplies the [[hypothalamus]].
Further research will need to be done to find how this occurs.<ref name=Maloney/>

====Breathing adaptations====

The common ostrich has no [[sweat glands]], and under heat stress they rely on panting to reduce their body temperature.<ref name=Schmidt-Nielsen/> [[endotherm|Panting]] increases [[heat transfer|evaporative heat]] (and water) loss from its respiratory surfaces, therefore forcing air and heat removal without the loss of metabolic salts.<ref name=Mitchell /> Panting allows the common ostrich to have a very effective respiratory evaporative water loss (REWL). Heat dissipated by respiratory evaporation increases linearly with ambient temperature, matching the rate of heat production.<ref name=Deeming /> As a result of panting the common ostrich should eventually experience alkalosis.<ref name=zool241 /> However, The CO<sub>2</sub> concentration in the blood does not change when hot ambient temperatures are experienced.<ref name=Schmidt-Nielsen/> This effect is caused by a [[Shunt (medical)|lung surface shunt]].<ref name=Schmidt-Nielsen/> The lung is not completely shunted, allowing enough oxygen to fulfill the bird's [[Metabolism|metabolic]] needs.<ref name=Schmidt-Nielsen/> The common ostrich utilizes [[Gular fluttering#Endothermy|gular fluttering]], rapid rhythmic contraction and relaxation of throat muscles, in a similar way to panting.<ref name=zool241 /> Both these behaviors allow the ostrich to actively increase the rate of evaporative cooling.<ref name=zool241 />
 
In hot temperatures water is lost via respiration.<ref name=zool241 /> Moreover, varying surface temperatures within the respiratory tract contribute differently to overall heat and water loss through panting.<ref name=Schmidt-Nielsen/> The surface temperature of the [[Gular skin|gular area]] is {{cvt|38|C}}, that of the [[Vertebrate trachea|tracheal area]] is between {{cvt|34|and|36|C}}, and that of both anterior and posterior air sacs is {{cvt|38|C}}.<ref name=Schmidt-Nielsen/> The long trachea, being cooler than body temperature, is a site of water evaporation.<ref name=Schmidt-Nielsen/>
 
As ambient air becomes hotter, additional evaporation can take place lower in the trachea making its way to the posterior sacs, shunting the lung surface.<ref name=Schmidt-Nielsen/> The trachea acts as a buffer for evaporation because of the length and the controlled vascularization.<ref name=Schmidt-Nielsen /> The Gular is also heavily vascularized; its purpose is for cooling blood, but also evaporation, as previously stated. Air flowing through the trachea can be either [[Laminar flow|laminar]] or [[Turbulence|turbulent]] depending on the state of the bird.<ref name=zool241 /> When the common ostrich is breathing normally, under no heat stress, air flow is laminar.<ref name=Schmidt-Nielsen/> When the common ostrich is experiencing heat stress from the environment the air flow is considered turbulent.<ref name=Schmidt-Nielsen/> This suggests that laminar air flow causes little to no heat transfer, while under heat stress turbulent airflow can cause maximum heat transfer within the trachea.<ref name=Schmidt-Nielsen/>

====Metabolism====
Common ostriches are able to attain their necessary energetic requirements via the [[redox|oxidation]] of absorbed nutrients. Much of the metabolic rate in animals is dependent upon their [[allometry]], the relationship between body size to shape, anatomy, physiology, and behavior of an animal. Hence, it is plausible to state that metabolic rate in animals with larger masses is greater than animals with a smaller mass.

When a bird is inactive and unfed, and the [[Room temperature|ambient temperature]] (i.e. in the [[thermal neutral zone|thermo-neutral zone]]) is high, the energy expended is at its minimum. This level of expenditure is better known as the [[Basal metabolic rate|basal metabolic rate (BMR)]], and can be calculated by measuring the amount of oxygen consumed during various activities.<ref name=Deeming/> Therefore, in common ostriches we see use of more energy when compared to smaller birds in absolute terms, but less per unit mass.

A key point when looking at the common ostrich metabolism is to note that it is a [[passerine|non-passerine]] bird. Thus, BMR in ostriches is particularly low with a value of only 0.113 mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>. This value can further be described using [[Kleiber's law]], which relates the BMR to the body mass of an animal.<ref name="Willmer_2009">{{cite book|last=Willmer|first=Pat|title=Environmental Physiology of Animals|year=2009|publisher=Wiley-Blackwell|isbn=978-1405107242|url=https://archive.org/details/environmentalphy00will}}</ref>

:Metabolic rate = 70''M''<sup>0.75</sup>

where ''M'' is body mass, and metabolic rate is measured in [[Calorie|kcal]] per day.

In common ostriches, a BMR (mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>) = 389&nbsp;kg<sup>0.73</sup>, describing a line parallel to the intercept with only about 60% in relation to other non-passerine birds.<ref name= Deeming/>

Along with BMR, energy is also needed for a range of other activities. If the [[Room temperature|ambient temperature]] is lower than the [[thermal neutral zone|thermo-neutral zone]], heat is produced to maintain [[Thermoregulation|body temperature]].<ref name=Deeming/> So, the metabolic rate in a resting, unfed bird, that is producing heat is known as the [[Basal metabolic rate|standard metabolic rate (SMR)]] or [[Basal metabolic rate|resting metabolic rate (RMR)]]. The common ostrich SMR has been seen to be approximately 0.26 mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>, almost 2.3 times the BMR.<ref name=Deeming/> On another note, animals that engage in extensive physical activity employ substantial amounts of energy for power. This is known as the maximum [[Allometry|metabolic scope]]. In an ostrich, it is seen to be at least 28 times greater than the BMR. Likewise, the daily energy [[Enzyme kinetics|turnover rate]] for an ostrich with access to free water is 12,700&nbsp;kJ&nbsp;d<sup>−1</sup>, equivalent to 0.26&nbsp;mL&nbsp;O<sub>2</sub>&nbsp;g<sup>−1</sup>&nbsp;h<sup>−1</sup>.<ref name=Deeming/>