Changes

==Why is it Important?==

==Why is it Important?==

Water has multiple functions: it is the solvent in which the majority of intra- and extracellular processes occur, it facilitates the transport of oxygen and nutrients in blood, it is needed for normal digestive function, [[Thermoregulation - Anatomy & Physiology|thermoregulation]] and the excretion of waste products. It is the major component of most body tissues accounting for approximately 60% of the total body weight in adult mammals with 2/3 in the Intracellular and 1/3 in the Extracellular compartment. Extracellular water is further dispersed between the interstitium (3/4) and plasma volume (1/4)<ref name="Wellman">Wellman ML, et al. Applied Physiology of Body Fluid in Dogs and Cats. In Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 2012 4th Ed. St. Louis: Elsevier Saunders  p.2-22.</ref>.

Water has multiple functions: it is the solvent in which the majority of intra- and extracellular processes occur, it facilitates the transport of oxygen and nutrients in blood, it is needed for normal digestive function, [[Thermoregulation - Anatomy & Physiology|thermoregulation]] and the excretion of waste products. It is the major component of most body tissues accounting for approximately 60% of the total body weight in adult mammals with 2/3 in the Intracellular and 1/3 in the Extracellular compartment. Extracellular water is further dispersed between the interstitium (3/4) and plasma volume (1/4)<ref name="Wellman">Wellman ML, et al. Applied Physiology of Body Fluid in Dogs and Cats. In Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 2012 4th Ed. St. Louis: Elsevier Saunders  p.2-22.</ref>.

Water balance is regulated by [[Pituitary Gland - Anatomy & Physiology#Antidiuretic Hormone|antidiuretic hormone]] (ADH) produced in the [[Hypothalamus - Anatomy & Physiology|hypothalamus]] and released in response to decrease in blood volume or increases in plasma osmolarity (determined mainly by plasma Na concentrations). Mild dehydration resulting in a loss of 0.5% fluid volume or an increase in [[Nutrition Glossary#Osmolality|osmolality]] of 1-3% stimulates production of ADH resulting in water reabsorption in the [[Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]] and activation of the [[Renin Angiotensin Aldosterone System|renin-angiotensin system]] with angiotensin II stimulating the thirst response<ref name="Robinson">Robinson EA and Adolph EF. Pattern of normal drinking in dogs. Am J Physiol 1943;139:39-44.</ref><ref name="Anderson">Anderson RS.Water balance in the dog and cat. J Small Animal Practice 1982;23:588-598.</ref><ref name="O'Connon">O’Connon WJ and Potts DJ. The external water exchange of normal laboratory dogs. Q J Exp Physiol  Cogn Med Sci 1969;54:244-265.</ref>.  

Water balance is regulated by [[Pituitary Gland - Anatomy & Physiology#Antidiuretic Hormone|antidiuretic hormone]] (ADH) produced in the [[Hypothalamus - Anatomy & Physiology|hypothalamus]] and released in response to decrease in blood volume or increases in plasma [[Nutrition Glossary#Osmolarity|osmolarity]] (determined mainly by plasma [[Sodium - Nutrition|Na]] concentrations). Mild dehydration resulting in a loss of 0.5% fluid volume or an increase in [[Nutrition Glossary#Osmolality|osmolality]] of 1-3% stimulates production of ADH resulting in water reabsorption in the [[Nephron Microscopic Anatomy#Proximal Tubule|renal tubules]] and activation of the [[Renin Angiotensin Aldosterone System|renin-angiotensin system]] with angiotensin II stimulating the thirst response<ref name="Robinson">Robinson EA and Adolph EF. Pattern of normal drinking in dogs. Am J Physiol 1943;139:39-44.</ref><ref name="Anderson">Anderson RS.Water balance in the dog and cat. J Small Animal Practice 1982;23:588-598.</ref><ref name="O'Connon">O’Connon WJ and Potts DJ. The external water exchange of normal laboratory dogs. Q J Exp Physiol  Cogn Med Sci 1969;54:244-265.</ref>.

==Regulation of Water Balance==

==Regulation of Water Balance==

====Water Losses:====

====Water Losses:====

#'''Urine''': Obligatory water loss is the minimal urine output required to eliminate metabolic waste products (including urea and minerals). Diets that provide protein and mineral intake in excess of daily requirements will cause an increase in urine output<ref name="Cizek">Cizek LT. Long-term observations on relationship between food and water ingestion in the dog. Am J Physiol 1959;197:324-326.</ref>. In contrast to obligatory water loss, free water does not contain additional solutes. Free water loss through urine is regulated by ADH at the level of the renal tubule and the amount of free water lost each day will depend on water intake, total body water needs, and health status.  

#'''Urine''': Obligatory water loss is the minimal urine output required to eliminate metabolic waste products (including [[urea]] and minerals). Diets that provide [[Protein - Nutrition|protein]] and [[Minerals - Nutrition|mineral]] intake in excess of daily requirements will cause an increase in urine output<ref name="Cizek">Cizek LT. Long-term observations on relationship between food and water ingestion in the dog. Am J Physiol 1959;197:324-326.</ref>. In contrast to obligatory water loss, free water does not contain additional solutes. Free water loss through urine is regulated by ADH at the level of the renal tubule and the amount of free water lost each day will depend on water intake, total body water needs, and health status.  

#'''Faeces''': Water that enters the gastrointestinal tract (either through diet, voluntary intake, or endogenous secretions) is effectively reabsorbed through both the [[Small Intestine Overview - Anatomy & Physiology|small]] and [[Large Intestine Overview - Anatomy & Physiology|large intestines]]. Compromised function ([[vomiting]], [[diarrhoea]]) can result in excess water loss.

#'''Faeces''': Water that enters the gastrointestinal tract (either through diet, voluntary intake, or endogenous secretions) is effectively reabsorbed through both the [[Small Intestine Overview - Anatomy & Physiology|small]] and [[Large Intestine Overview - Anatomy & Physiology|large intestines]]. Compromised function ([[vomiting]], [[diarrhoea]]) can result in excess water loss.

#'''Respiratory Epithelium''': Respiratory water loss will fluctuate depending on ambient temperature, humidity, and activity. At higher temperatures dogs will increase respiratory rate by 12-20 times and cats by 4.5 times<ref name="Wellman"/> to facilitate cooling, which correlates with an average loss of 469 ml/day for a panting dog versus 41 ml/day for an average cat. Dogs at rest in a thermoneutral environment will have an evaporative loss of <1 ml/kg/hr, while during periods of activity losses can reach up to 7 ml/kg/hr<ref name="Caldwell">Caldwell GT. Studies in water metabolism of the cat. Physiol Zool 1931;4:324-359.</ref>.

#'''Respiratory Epithelium''': Respiratory water loss will fluctuate depending on ambient temperature, humidity, and activity. At higher temperatures dogs will increase respiratory rate by 12-20 times and cats by 4.5 times<ref name="Wellman"/> to facilitate cooling, which correlates with an average loss of 469 ml/day for a panting dog versus 41 ml/day for an average cat. Dogs at rest in a thermoneutral environment will have an evaporative loss of <1 ml/kg/hr, while during periods of activity, losses can reach up to 7 ml/kg/hr<ref name="Caldwell">Caldwell GT. Studies in water metabolism of the cat. Physiol Zool 1931;4:324-359.</ref>.

#'''Cutaneous Evaporation''': Cutaneous evaporation is not considered a significant source of water loss in dogs and cats as sweat glands are limited to the foot pads.

#'''Cutaneous Evaporation''': Cutaneous evaporation is not considered a significant source of water loss in dogs and cats as sweat glands are limited to the foot pads.

==Roles in the Body==

==Roles in the Body==

Water maintains circulating volume; contributes to thermoregulation by evaporation; is necessary for elimination of waste products through the renal tubules; aids in digestion through secretions of body fluids within the gastrointestinal tract (e.g., saliva, bile fluid, pancreatic fluid), allows for interaction of food constituents and enzymes; forms an aqueous environment for metabolic processes and chemical reactions (e.g., hydrolysis); and is a major component of other body fluids such as joint fluid and [[Cerebral Spinal Fluid - Anatomy & Physiology|cerebrospinal fluid]]<ref name="Case"/>. Increased water intake can also be used as a preventative or therapeutic treatment for cats and dog with [[Cystitis|lower urinary tract disease]].

Water maintains circulating volume; contributes to thermoregulation by evaporation; is necessary for elimination of waste products through the renal tubules; aids in digestion through secretions of body fluids within the gastrointestinal tract (e.g. saliva, bile fluid, pancreatic fluid), allows for interaction of food constituents and enzymes; forms an aqueous environment for metabolic processes and chemical reactions (e.g. hydrolysis); and is a major component of other body fluids such as joint fluid and [[Cerebral Spinal Fluid - Anatomy & Physiology|cerebrospinal fluid]]<ref name="Case"/>. Increased water intake can also be used as a preventative or therapeutic treatment for cats and dog with [[:Category:Lower Urinary Tract - Pathology|lower urinary tract disease]].

==Consequence of Water Deficiency (Dehydration)==

==Consequence of Water Deficiency (Dehydration)==

Recognised syndromes influenced by subclinical dehydration in cats include:  

Recognised syndromes influenced by subclinical dehydration in cats include:  

#'''Crystalluria and [[Urolithiasis]]''': Chronic mild dehydration results in more concentrated urine production. Increased urine concentration with excess intake of crystal precursors may lead to an increased risk of crystalluria and subsequent urolithiasis. Crystals commonly encountered include [[Urolithiasis#Struvite|struvite]], but [[Urolithiasis#Calcium oxalate|calcium oxalate]] and [[Urolithiasis#Urate|urate]] crystals can also be seen in otherwise healthy adult cats.  

#'''Crystalluria and [[Urolithiasis]]''': Chronic mild dehydration results in more concentrated urine production. Increased urine concentration with excess intake of crystal precursors may lead to an increased risk of crystalluria and subsequent urolithiasis. Crystals commonly encountered include [[Urolithiasis#Struvite|struvite]], but [[Urolithiasis#Calcium oxalate|calcium oxalate]] and [[Urolithiasis#Urate|urate]] crystals can also be seen in otherwise healthy adult cats.  

#'''[[Cystitis|Feline urologic syndrome (FUS)]]''': Also called feline lower urinary tract disease (FLUTD) is believed to be highly influenced by the concentration of urine. High urine concentrations can exacerbate clinical signs of FUS. Increased risk of FUS has been associated with eating dry diets<ref name="Buffington">Buffington CA, et al. Clinical evaluation of cats with non-obstructive urinary tract disease. JAVMA 1997;210(1):46-50.</ref>. Therefore, feeding higher moisture diets (e.g., wet foods) is often recommended to reduce the risk of FUS and improve clinical signs of [[Category:Lower Urinary Tract - Anatomy & Physiology|lower urinary tract]] health in cats<ref name="Markwell">Markwell PJ, et al. Clinical evaluation of commercially available urinary acidifying diets in the management of idiopathic cystitis. JAVMA 1999;214(3):361-365.</ref>.

#'''[[Cystitis|Feline urologic syndrome (FUS)]]''': Also called feline lower urinary tract disease (FLUTD) is believed to be highly influenced by the concentration of urine. High urine concentrations can exacerbate clinical signs of FUS. Increased risk of FUS has been associated with eating dry diets<ref name="Buffington">Buffington CA, et al. Clinical evaluation of cats with non-obstructive urinary tract disease. JAVMA 1997;210(1):46-50.</ref>. Therefore, feeding higher moisture diets (e.g. wet foods) is often recommended to reduce the risk of FUS and improve clinical signs of [[:Category:Lower Urinary Tract - Anatomy & Physiology|lower urinary tract]] health in cats<ref name="Markwell">Markwell PJ, et al. Clinical evaluation of commercially available urinary acidifying diets in the management of idiopathic cystitis. JAVMA 1999;214(3):361-365.</ref>.

==Toxicity==

==Toxicity==

Water toxicity is rare in dogs and cats. Water intake in excess of need is excreted as free water through the renal tubules. Over-consumption can be induced in animals that are offered water ad libitum following prolonged [[dehydration]], exercise, or prolonged heat exposure<ref name="NRC"/>. Clinical sings of water toxicity include seizures, ataxia, and coma.

Water toxicity is rare in dogs and cats. Water intake in excess of need is excreted as free water through the renal tubules. Over-consumption can be induced in animals that are offered water ad libitum following prolonged [[dehydration]], exercise, or prolonged heat exposure<ref name="NRC"/>. Clinical sings of water toxicity include [[seizures]], ataxia, and coma.

==Sources of Water==

==Sources of Water==

#'''Dietary moisture''' content can range from 7% as fed in a dry commercial diet to greater than 80% as fed in a wet diet.  

#'''Dietary moisture''' content can range from 7% as fed in a dry commercial diet to greater than 80% as fed in a wet diet.  

#'''Voluntary intake (drinking)''' is influenced by ambient temperature, the diet type and amount fed, exercise demands, physiologic state, and health status.  

#'''Voluntary intake (drinking)''' is influenced by ambient temperature, the diet type and amount fed, exercise demands, physiologic state, and health status.  

#'''Metabolic water production''' occurs during oxidation of energy containing [[Nutrition Glossary#Macronutrient|macronutrients]] (i.e. protein, fat, and carbohydrates) and constitutes the smallest contribution to the total water intake (10-15%) of an animal<ref name="Anderson"/>. The volume of metabolic water produced will also vary with the macronutrient composition of the food; fat oxidation produces the largest water volume (107 ml/100 g), compared to protein (55 ml/100 g) and carbohydrates (41 ml/100 g)<ref name="Case"/>.

#'''Metabolic water production''' occurs during oxidation of energy containing [[Nutrition Glossary#Macronutrient|macronutrients]] (i.e. protein, fat, and carbohydrates) and constitutes the smallest contribution to the total water intake (10-15%) of an animal<ref name="Anderson"/>. The volume of metabolic water produced will also vary with the macronutrient composition of the food; [[Fat Overview - Nutrition|fat]] oxidation produces the largest water volume (107 ml/100 g), compared to [[Protein - Nutrition|protein]] (55 ml/100 g) and [[Carbohydrates Overview - Nutrition|carbohydrates]] (41 ml/100 g)<ref name="Case"/>.

==Diagnosis of [[Dehydration]]==

==Diagnosis of [[Dehydration]]==

==References==

==References==

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[[Category:Nutrients]]

[[Category:Nutrients]]