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Exotic Urinary System - Anatomy & Physiology (view source)
Revision as of 14:44, 5 July 2012
, 14:44, 5 July 2012→Other Roles of the Reptilian Kidney
==Introduction==
This section is devoted specifically to the renal anatomy and physiology of fish, aquatic and terrestrial amphibians, birds and reptiles. These animals excrete nitrogenous waste differently to domestic mammals, this combined with the very different habitats where these animals exist results in a variety of different renal mechanisms and appearances.
This section is devoted specifically to the renal anatomy and physiology of fish, aquatic and terrestrial amphibians, birds and reptiles. These animals excrete nitrogenous waste differently to domestic mammals, this combined with the very different habitats where these animals exist results in a variety of different renal mechanisms and appearances.
* Some organisms excrete nitrogen directly as ammonia
* Some organisms excrete nitrogen directly as ammonia
* They are known as '''ammonotelic''' organisms
* This is how fish and aquatic amphibians excrete nitrogenous waste
* This is how fish and aquatic amphibians excrete nitrogenous waste
* Relatively toxic but it is better tolerated by aquatic animals
* Relatively toxic but it is better tolerated by aquatic animals due to dilution
* 400ml of water is also excreted per gram of ammonia making this an unrealistic option for terrestrial organisms
* 400ml of water is also excreted per gram of ammonia making this an unrealistic option for terrestrial organisms
====Urea====
====Urea====
* Some animals process ammonia into urea
* Some animals process ammonia into urea
* They are known as '''ureotelic''' organisms
* Mammals and terrestrial amphibians
* Mammals and terrestrial amphibians
* 40ml of water is excreted per gram of urea excreted
* 40ml of water is excreted per gram of urea excreted
* Urea is very soluble and non-toxic
====Uric Acid====
====Uric Acid====
* Referred to as Uricotelism
* Referred to as '''Uricotelism'''
* Urea is further processed to uric acid
* Urea is further processed to uric acid
* Carried out by birds and reptiles
* Carried out by birds and reptiles
* Only 8ml of water is co-excreted per gram
* Only 8ml of water is co-excreted per gram
* Highly insoluble
* Highly insoluble and less toxic than ammonia, though it can precipitate into body cavities
==Fish==
==Fish==
====Anatomy====
====Anatomy====
Fish have a single kidney which is the same length as the coelom. It can be divided up into cranial and caudal parts; the cranial part has endocrine and haematopoietic functions and the caudal is where filtration occurs. It is not uncommon for some species to have no glomeruli however as a rule freshwater fish have larger glomeruli is greater numbers. Some species also have renal portal veins.
Fish have a single kidney which is the same length as the coelom. It can be divided up into cranial and caudal parts; the cranial part has endocrine and haematopoietic functions and the caudal is where filtration occurs. It is not uncommon for some species to have no glomeruli however as a rule freshwater fish have larger glomeruli in greater numbers. Some species also have renal portal veins.
====Osmoregulation====
====Osmoregulation====
=====Saltwater=====
=====Saltwater=====
The environment is hypotonic compared to the body of the fish therefore water is lost across their gills so they drink sea water to replace this which results in a large intake of salt (activates Angiotensin 2). They excrete both ammonia and NaCl across their gills and further NaCl across their skin. Their kidneys have small or absent glomeruli and their main function is the elimination of excess divalent ions e.g. Mg<sup>2+</sup>
The environment is hypertonic compared to the body of the fish therefore water is lost across their gills so they drink sea water to replace this which results in a large intake of salt (activates Angiotensin 2). They excrete both ammonia and NaCl across their gills and further NaCl across their skin. Their kidneys have small or absent glomeruli and their main function is the elimination of excess divalent ions e.g. Mg<sup>2+</sup>
==Amphibian==
==Amphibian==
==Avian==
==Avian==
[[Image:avrenalanattri.jpg|right|thumb|300px|<small><center>A schematic showing the vascularisation of the avian kidneys, specifically the renal portal structure. N.B. the renal arteries have been excluded</center></small>]]
====Anatomy====
====Anatomy====
====Salt glands====
====Salt glands====
These glands are found in desert and aquatic birds as salt consumption exceeds renal clearance. These supraorbital glands drain into the nostrils and account for 20% of total NaCl excretion. They are not under the control of kidneys and the hypertrophy if the birds salt intake increases
These glands are found in desert and aquatic birds as salt consumption exceeds renal clearance. These supraorbital glands drain into the nostrils and account for 20% of total NaCl excretion. They are not under the control of kidneys and they hypertrophy if the birds salt intake increases.
====Avian Renal Portal System====
In birds the blood from the hindlimbs is carried directly to the kidneys. The cranial and caudal renal portal veins deliver blood from the hindlimbs into the capillary beds of the interlobar arteries. Therefore blood which has already been through capillary beds in the hind limbs mixes with blood directly from the heart. It bypasses the glomeruli and waste products in the blood are secreted directly into the tubules. This is thought to be a more efficent way to excrete uric acid and urate. A portal valve regulates how much blood from the hindlimbs passes through the kidneys. When open very little blood enters the capillary beds as it follows the path of least resistance. If the valve narrows then blood is forced into the capillary beds. However some blood always escapes thanks to connections with both the caudal mesenteric veins and vertebral sinuses. It is of significance when injecting these animals if the injection is given in the caudal half of the body most of the drug will be potentially lost in the urine before it has time to act it may also be toxic to the kidney as it has not been metabolised by the liver
====Other Roles of the Avian Kidney====
====Other Roles of the Avian Kidney====
====Uric Acid Secretion in Reptiles====
====Uric Acid Secretion in Reptiles====
Uric acid is secreted into the proximal tubules actively using potassium and into the bladder (where present) is response to H<sup+</sup> secretion. The secretion of urate increases in response to a decrease in blood pH.
Uric acid is secreted into the proximal tubules actively using potassium and into the bladder (where present) is response to H<sup>+</sup> secretion. The secretion of urate increases in response to a decrease in blood pH.
*** Response to stress
*** Response to stress
*** Blood bypasses kidney
*** Blood bypasses kidney
=====Significance=====
*This means if the animal is stressed and is injected in the caudal half of the body the drug will have greater effects as it will not be filtered
*If the animal is not stressed most of the drug will be potentially lost in the urine before it has time to act it may also be toxic to the kidney as it has not been metabolised by the liver
*This is why it is best to inject them in the cranial half of the body
====Reptilian Salt Glands====
====Reptilian Salt Glands====
* Sea turtles have modified tear glands which allow them to secrete salt from their eyes
* Sea turtles have modified tear glands which allow them to secrete salt from their eyes
====Other Roles of the Reptilian Kidney====
==== Other Roles of the Reptilian Kidney ====
*Activates vitamin D
*Synthesises Vitamin C
[[Category:Urinary_System_-_Anatomy_&_Physiology]] [[Category:Birds - Urinary System]]
[[Category:Bullet Points]]