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New page: {{review}} {{toplink |linkpage =General Pathology |linktext =General Pathology |maplink = General Pathology (Content Map) |pagetype =Pathology |sublink1=Circulatory Disorders - Pathology...
{{review}}
{{toplink
|linkpage =General Pathology
|linktext =General Pathology
|maplink = General Pathology (Content Map)
|pagetype =Pathology
|sublink1=Circulatory Disorders - Pathology
|subtext1=CIRCULATORY DISORDERS
}}
<br>
==Introduction==
* Body fluid is composed of body water and the solutes dissolved within it.
** Forms the bulk of the cell protoplasm.
** Acts as the transport medium for metabolites.
** Transports waste products to the exterior of the body.
* The electrolytes dissolved in body water are important.
** Potassium, calcium and magnesium are required for normal cell function.
** Sodium and chloride are important for the maintenance of extracellular osmotic pressure.
** Bicarbonate contributed to regulation of the extracellular pH.
* 60 - 70% of the lean body weight is made up by body water.
** This is about 5% less in females.
===Distribution of body water===
* Body fluid is comprised of aroung '''60% intracellular''' fluid, and '''40% extracelluar''' fluid.
** Fluid is able to move between these states.
* Extracellular fluid can be further divided to:
** '''Intravascular plasma''' (8%)
** '''Transcellular fluid'''
*** Cerebo-spinal fluid
*** Occular humours
*** Serous fluid
*** Synovial fluid
*** Digestive juice
** '''Interstitial fluid'''
*** Tissue fluid around cells.
* Transcelllar and interstitial fluid combined make up the other 32% of the 40% extracellular fluid.
==Whole Body Fluid Exchange==
* There is a balance between the interstitial fluid compartment and plasma.
** This results in a controlled environment for the body cells.
===Mechanisms of Fluid Balance===
* There are three main mechanisms that regulate fluid balance between the body and the external environment.
*# '''Mechanisms regulating renal water output'''
*#* e.g. anti-diuretic hormone (ADH).
*# '''Mechanisms regulating renal sodium and water balance''', e.g.
*#* Glomerular filtration rate.
*#* The angiotension - aldosterone loop.
*# '''Mechanism of thirst'''
*#* Controlled by the central nervous centre and the baroreceptors (vascular pressure receptors).
* It is likely that the effect of natriuretic hormone on blood levels of sodium also plays a role.
* There is also a certain amount of internal fluid turnover, in the
** '''Gut'''
*** Fluid leaves the blood to the digestive glands and organs. It is secreted to the gut lumen before reabsorption to the blood.
** '''Kidneys'''
*** Fluid leaves the blood, passes through the glomerulus and tubules and rejoins the blood.
** ''' CNS'''
*** Fluid from the blood passes to the choroid plexus to the CSF, before later rejoining the blood.
** '''Capillaries'''
*** Fluid from the blood joins the interstitial fluid before rejoining the blood via the lymphatics
==Tissue Fluid Exchange==
* Capillaries are a relatively closed system of vessels.
** Metabolites diffuse through the endothelium into the tissue fluid .
* Metabolite diffusion and water exchange depends on:
*# Hydrostatic pressure at the arteriolar end of the vascular network.
*# Osmotic pressure of the plasma proteins relative to interstitial proteins, at the venous end of the vascular network.
*# Osmolality of plasma compared to interstitial fluid as a result of changes in distribution of sodium, chloride and other ions.
===Tissue Fluid Exchange At Rest===
* At rest, fluid and solutes are forced out of the arteriolar end into the tissue spaces by hydrostatic pressure.
* The osmotic pressure of plasma proteins at the venous end exceeds venous hydrostatic pressure.
** Fluid is reabsorbed.
** The main plasma protein is albumin.
* Approximately equal volumes of fluids are exchanged.
** A small surplus of fluid is supplied to the tissues.
*** This is absorbed by the lymphatic system.
===Tissue Fluid Exchange in Activity States===
* For example, in muscle action of glandular secretion.
* There is enhanced temporary formation of tissue fluid.
* This formation of tissue fluid results from:
*# '''Vascular Events'''
*#* Blood flow is increased as a result of:
*#** Increases arteriolar pressure and cardiac output.
*#** Capillary dilatation.
*# ''' Production of metabolic wastes'''
*#* Osmotically active molecules are produced.
*#** For example, lactic acid and urea.
* At the end of activity, the excess fluid may be:
** Secreted (if glandular).
** Metabolised/ voided.
** Retained temporarily in tissues and slowly reabsorbed
** Absorbed by lymphatics.
==Abnormal States of Sodium and Water Balance==
* Water and sodium are intimately related.
** Imbalance of one tends to lead to upset in the other.
** Cellular function is disrupted by imbalance.
===Water Deficiency===
====Causes====
* '''Decreased intake'''.
** The animal is disinclined or unabled to drink.
** May be due to general debility or because of obstruction to the mouth/throuat by disease lesions.
* '''Deprivation of water'''.
** Animal loses access to its water supply.
* '''Increased uncontrolled physiological loss'''
** For example, due to hyperventilation, excessive sweating, or polyuria due to renal disease.
====Effects====
* Electrolytes are not depleted, although water is.
** There is therefore an increase in osmolality of the extracellular fluid.
*** Intracellular water is transferred to ECF, resulting in cellular dehydration results.
**** Causes cell death.
* Cellular dehydration particularly affects the CNS and heart.
===Deficiency of Both Sodium and Water===
* Known as "salt depletion".
* The effects of the sodium (and therefore chloride) loss predominate.
** There is clinically detectable dehydration.
====Causes====
* '''Gastro-intestinal disorders'''.
** [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|Vomiting]] and [[Intestine Diarrhoea - Pathology|diarrhoea]].
* '''Gut crises'''.
** [[Intestine Physical Disturbances - Pathology#Obstruction|Intestinal obstruction]].
** [[Intestine Physical Disturbances - Pathology#Positional Changes/ Displacements|Torsions]].
** Ruminal/ abomasal impaction.
* '''Excessive and prolonged sweating'''.
** Heat exhaustion.
* '''Renal disease'''.
** Nephritis.
** May also be associated with diabetes mellitus toxicity.
* '''Severe haemorrhage or burns'''.
** Result in severe plasma losses.
====Effects====
* Loss of sodium and chloride reduces the osmolality of extracellular fluid.
** There is a simultaneous loss of water.
* Water is transferred from the ECF to cells.
** Cells over-hydrate and may rupture.
* ECF volume falls.
** Resultis in haemoconcentration and peripheral circulatory failure.
* Renal involvement may become significant.
===Water Excess===
* Known as "water intoxication".
====Causes====
* Results from induced hypo-osmolality, e.g.
** Excessive administration of water to previously deprived animals.
** Administration of large volumes of water to animals with acute renal failure.
====Effects====
* The ECF osmolality is reduced.
* Water is transferred to the cells and they become "water-logged".
** Intracellular oedema in the CNS results in convulsions and death.
===Excess of Both Sodium and Water===
* Uncommon.
* When it does occur, it is an iatrogenic condition.
** For example, administering excess saline solutions in animals with impaired renal function.
===Sodium Excess===
* Known as "salt poisoning".
* Occurs sporadically in the U.K. as a group or herd problem in intensive systems.
* Mainly affects pigs and poultry.
* Caused by:
** Accidental ingestion of excess salt
*** Either by dietary contamination, or error.
** Deprivation of water on relatively high salt diets.
*** This is the more likely scenario.
* Salt poisioning may be
** Peracute/ acute
** Subacute/ chronic
====Peracute / acute====
* Peracute cases are often found dead.
** Only shock haemorrhages are seen at autopsy.
* Acute cases present as abdominal pain, diarrhoea and vomiting.
** Death occurs in 24 - 48 hours.
** At autosy, may see:
*** Shock haemorrhages.
*** Gut congestion.
*** Fluid accumulations in body cavities.
====Subacute / chronic====
* These cases show nervous signs.
** Convulsions
** Blindness
** Ataxia
* Show excessive salivation.
* May be polyuric.
* Fluid may accumulate subcutaneouslt and in the abdomen.
* Macroscopic findings are inconclusive.
====Diagnosis====
* For definitave diagnosis, histological examination is required.
* On histological examination, the following may be seen:
** Perineuronal vasculation and cerebral neuronal necrosis.
*** '''Polio-encephalomalacia'''.
** Eosinophilic meningoencephalitis.
** Perivascular oedema in the brain.
==Abnormal States of Potassium, Magnesium and Calcium Balance==
===Hypomagnesaemia===
* Magnesium is important for muscular and nervous conduction.
*Low Mg <sup>++</sup> diets may induce acute hypo-magnesaemia in lactating cows.
** Seen as tremors and convulsions (tetany).
** For example, poor quality silage.
* High K<sup>+</sup> diets induce a relative Mg<sup>++</sup> imbalance.
** For example, lush pasture.
** Known as "grass staggers".
** Produces tetany and ataxia, and sometimes cardiac arrest.
** Only shock haemorrhages can be seen at autopsy; i.e. non-specific findings.
===Hypokalaemia===
* Potasstium is important for nervous and muscle conduction, especially in cardiac muscle.
* The hypokalaemia is associated with diarrhoea and dehydration in calves.
** Animals die from cardiac arrest following ventricular dissociation.
===Calcium===
* '''Hypocalcaemia''' is most significant.
** "Milk fever" in lactating cattle.
** Eclampsia (parturient tetany) in bitches.
* '''Hypercalcaemia''' is less common.
** Usually the result of dietary imbalance.
** Produces metastatic vascular calcification.
{{toplink
|linkpage =General Pathology
|linktext =General Pathology
|maplink = General Pathology (Content Map)
|pagetype =Pathology
|sublink1=Circulatory Disorders - Pathology
|subtext1=CIRCULATORY DISORDERS
}}
<br>
==Introduction==
* Body fluid is composed of body water and the solutes dissolved within it.
** Forms the bulk of the cell protoplasm.
** Acts as the transport medium for metabolites.
** Transports waste products to the exterior of the body.
* The electrolytes dissolved in body water are important.
** Potassium, calcium and magnesium are required for normal cell function.
** Sodium and chloride are important for the maintenance of extracellular osmotic pressure.
** Bicarbonate contributed to regulation of the extracellular pH.
* 60 - 70% of the lean body weight is made up by body water.
** This is about 5% less in females.
===Distribution of body water===
* Body fluid is comprised of aroung '''60% intracellular''' fluid, and '''40% extracelluar''' fluid.
** Fluid is able to move between these states.
* Extracellular fluid can be further divided to:
** '''Intravascular plasma''' (8%)
** '''Transcellular fluid'''
*** Cerebo-spinal fluid
*** Occular humours
*** Serous fluid
*** Synovial fluid
*** Digestive juice
** '''Interstitial fluid'''
*** Tissue fluid around cells.
* Transcelllar and interstitial fluid combined make up the other 32% of the 40% extracellular fluid.
==Whole Body Fluid Exchange==
* There is a balance between the interstitial fluid compartment and plasma.
** This results in a controlled environment for the body cells.
===Mechanisms of Fluid Balance===
* There are three main mechanisms that regulate fluid balance between the body and the external environment.
*# '''Mechanisms regulating renal water output'''
*#* e.g. anti-diuretic hormone (ADH).
*# '''Mechanisms regulating renal sodium and water balance''', e.g.
*#* Glomerular filtration rate.
*#* The angiotension - aldosterone loop.
*# '''Mechanism of thirst'''
*#* Controlled by the central nervous centre and the baroreceptors (vascular pressure receptors).
* It is likely that the effect of natriuretic hormone on blood levels of sodium also plays a role.
* There is also a certain amount of internal fluid turnover, in the
** '''Gut'''
*** Fluid leaves the blood to the digestive glands and organs. It is secreted to the gut lumen before reabsorption to the blood.
** '''Kidneys'''
*** Fluid leaves the blood, passes through the glomerulus and tubules and rejoins the blood.
** ''' CNS'''
*** Fluid from the blood passes to the choroid plexus to the CSF, before later rejoining the blood.
** '''Capillaries'''
*** Fluid from the blood joins the interstitial fluid before rejoining the blood via the lymphatics
==Tissue Fluid Exchange==
* Capillaries are a relatively closed system of vessels.
** Metabolites diffuse through the endothelium into the tissue fluid .
* Metabolite diffusion and water exchange depends on:
*# Hydrostatic pressure at the arteriolar end of the vascular network.
*# Osmotic pressure of the plasma proteins relative to interstitial proteins, at the venous end of the vascular network.
*# Osmolality of plasma compared to interstitial fluid as a result of changes in distribution of sodium, chloride and other ions.
===Tissue Fluid Exchange At Rest===
* At rest, fluid and solutes are forced out of the arteriolar end into the tissue spaces by hydrostatic pressure.
* The osmotic pressure of plasma proteins at the venous end exceeds venous hydrostatic pressure.
** Fluid is reabsorbed.
** The main plasma protein is albumin.
* Approximately equal volumes of fluids are exchanged.
** A small surplus of fluid is supplied to the tissues.
*** This is absorbed by the lymphatic system.
===Tissue Fluid Exchange in Activity States===
* For example, in muscle action of glandular secretion.
* There is enhanced temporary formation of tissue fluid.
* This formation of tissue fluid results from:
*# '''Vascular Events'''
*#* Blood flow is increased as a result of:
*#** Increases arteriolar pressure and cardiac output.
*#** Capillary dilatation.
*# ''' Production of metabolic wastes'''
*#* Osmotically active molecules are produced.
*#** For example, lactic acid and urea.
* At the end of activity, the excess fluid may be:
** Secreted (if glandular).
** Metabolised/ voided.
** Retained temporarily in tissues and slowly reabsorbed
** Absorbed by lymphatics.
==Abnormal States of Sodium and Water Balance==
* Water and sodium are intimately related.
** Imbalance of one tends to lead to upset in the other.
** Cellular function is disrupted by imbalance.
===Water Deficiency===
====Causes====
* '''Decreased intake'''.
** The animal is disinclined or unabled to drink.
** May be due to general debility or because of obstruction to the mouth/throuat by disease lesions.
* '''Deprivation of water'''.
** Animal loses access to its water supply.
* '''Increased uncontrolled physiological loss'''
** For example, due to hyperventilation, excessive sweating, or polyuria due to renal disease.
====Effects====
* Electrolytes are not depleted, although water is.
** There is therefore an increase in osmolality of the extracellular fluid.
*** Intracellular water is transferred to ECF, resulting in cellular dehydration results.
**** Causes cell death.
* Cellular dehydration particularly affects the CNS and heart.
===Deficiency of Both Sodium and Water===
* Known as "salt depletion".
* The effects of the sodium (and therefore chloride) loss predominate.
** There is clinically detectable dehydration.
====Causes====
* '''Gastro-intestinal disorders'''.
** [[Control of Feeding - Anatomy & Physiology#The Vomit Reflex|Vomiting]] and [[Intestine Diarrhoea - Pathology|diarrhoea]].
* '''Gut crises'''.
** [[Intestine Physical Disturbances - Pathology#Obstruction|Intestinal obstruction]].
** [[Intestine Physical Disturbances - Pathology#Positional Changes/ Displacements|Torsions]].
** Ruminal/ abomasal impaction.
* '''Excessive and prolonged sweating'''.
** Heat exhaustion.
* '''Renal disease'''.
** Nephritis.
** May also be associated with diabetes mellitus toxicity.
* '''Severe haemorrhage or burns'''.
** Result in severe plasma losses.
====Effects====
* Loss of sodium and chloride reduces the osmolality of extracellular fluid.
** There is a simultaneous loss of water.
* Water is transferred from the ECF to cells.
** Cells over-hydrate and may rupture.
* ECF volume falls.
** Resultis in haemoconcentration and peripheral circulatory failure.
* Renal involvement may become significant.
===Water Excess===
* Known as "water intoxication".
====Causes====
* Results from induced hypo-osmolality, e.g.
** Excessive administration of water to previously deprived animals.
** Administration of large volumes of water to animals with acute renal failure.
====Effects====
* The ECF osmolality is reduced.
* Water is transferred to the cells and they become "water-logged".
** Intracellular oedema in the CNS results in convulsions and death.
===Excess of Both Sodium and Water===
* Uncommon.
* When it does occur, it is an iatrogenic condition.
** For example, administering excess saline solutions in animals with impaired renal function.
===Sodium Excess===
* Known as "salt poisoning".
* Occurs sporadically in the U.K. as a group or herd problem in intensive systems.
* Mainly affects pigs and poultry.
* Caused by:
** Accidental ingestion of excess salt
*** Either by dietary contamination, or error.
** Deprivation of water on relatively high salt diets.
*** This is the more likely scenario.
* Salt poisioning may be
** Peracute/ acute
** Subacute/ chronic
====Peracute / acute====
* Peracute cases are often found dead.
** Only shock haemorrhages are seen at autopsy.
* Acute cases present as abdominal pain, diarrhoea and vomiting.
** Death occurs in 24 - 48 hours.
** At autosy, may see:
*** Shock haemorrhages.
*** Gut congestion.
*** Fluid accumulations in body cavities.
====Subacute / chronic====
* These cases show nervous signs.
** Convulsions
** Blindness
** Ataxia
* Show excessive salivation.
* May be polyuric.
* Fluid may accumulate subcutaneouslt and in the abdomen.
* Macroscopic findings are inconclusive.
====Diagnosis====
* For definitave diagnosis, histological examination is required.
* On histological examination, the following may be seen:
** Perineuronal vasculation and cerebral neuronal necrosis.
*** '''Polio-encephalomalacia'''.
** Eosinophilic meningoencephalitis.
** Perivascular oedema in the brain.
==Abnormal States of Potassium, Magnesium and Calcium Balance==
===Hypomagnesaemia===
* Magnesium is important for muscular and nervous conduction.
*Low Mg <sup>++</sup> diets may induce acute hypo-magnesaemia in lactating cows.
** Seen as tremors and convulsions (tetany).
** For example, poor quality silage.
* High K<sup>+</sup> diets induce a relative Mg<sup>++</sup> imbalance.
** For example, lush pasture.
** Known as "grass staggers".
** Produces tetany and ataxia, and sometimes cardiac arrest.
** Only shock haemorrhages can be seen at autopsy; i.e. non-specific findings.
===Hypokalaemia===
* Potasstium is important for nervous and muscle conduction, especially in cardiac muscle.
* The hypokalaemia is associated with diarrhoea and dehydration in calves.
** Animals die from cardiac arrest following ventricular dissociation.
===Calcium===
* '''Hypocalcaemia''' is most significant.
** "Milk fever" in lactating cattle.
** Eclampsia (parturient tetany) in bitches.
* '''Hypercalcaemia''' is less common.
** Usually the result of dietary imbalance.
** Produces metastatic vascular calcification.