Regulation of Fluid and Electrolyte Balance Prof. K. Sivapalan.
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Transcript of Regulation of Fluid and Electrolyte Balance Prof. K. Sivapalan.
Regulation of Fluid and Electrolyte Balance
Prof. K. Sivapalan
Regulation of fluid and electrolytes 2
Regulation of Fluid and Electrolyte Balance
• Consumption of water can increase volume but reduce the osmolality of the fluids.
• Consumption of salt and other substances alter the osmolality and through that the volume of fluid compartments.
• The constancy of the composition and volume of the fluid compartments is maintained by many inter-related physiological mechanisms.
June 2013
Regulation of fluid and electrolytes 3
Regulation of Osmolality
• Osmoreceptors are located in anterior Hypothalamus.
• Stimulated by increase in osmolality of plasma and stimulate thirst- drinking water [?amount to balance osmolality].
• Anti diuretic Hormone secreation by posterior piotuitary is increased
• ADH acts in Kidney to reduce water excretion in urine.
June 2013
Regulation of fluid and electrolytes 4
Renal Excretion of Water and Electrolytes
• About 180 liters are flitered.
• About 7/8 reabsorbed in PCT
• Rest in the other portions of the tubule.
• About 18 liters of water absorbed in collecting dut under ADH
June 2013
Regulation of fluid and electrolytes 5
Effects of Drinking Water
June 2013
Drinking water dilutes plasma.
But due to inhibition of ADH secretion urine flow increases within 30 minutes without increase in solute excretion.
In about 2-2.5 hours excess water is eliminated.
Reverse occurs in dehydration
Regulation of fluid and electrolytes 6
Thirst Mechanism
• Increase in plasma osmolarity [even small- 2 mOsm of NaCl] provokes thirst and drinking.
• Salt appetite is increased consumption of salt in salt depletion.
June 2013
Regulation of fluid and electrolytes 7
Regulation of Volume
• Body fluid volume reflects on blood volume.
• Large veins and right atrium contain “volume receptors” in their walls.
• Distention increases and collapse reduces impulses sent to Hypothalamus to regulate ADH secretion.
• After reduction of 10 % of the blood.
June 2013
Regulation of fluid and electrolytes 8
Control of Sodium Balance
• Sodium is the main osmotic substance in plasma.
• Sodium balance [and the osmolarity of the plasma] is controlled by renin- angeotensin- aldesteron mechanism.
• Renin converts Angeotensinogen to Angeotensin I. In lung paranchyma, it is converted to Angeotensin II.
June 2013
Regulation of fluid and electrolytes 9
Aldosterone
• Angeotensin II stimulates secretion of aldosterone from Adrenal Cortex.
• Aldosterone increases sodium absorption in renal tubules, preventing excretion.
June 2013
Regulation of fluid and electrolytes 10
Over Hydration- Oedema
• Oedema is a condition seen as swelling
• Occurs when interstitial fluid is more than usual- increased filtration or reduced re-absorption.
• The cells are far apart and tissue pressure increases depending on the tension of the covering- skin, fascia or bone (brain).
• Reduced re-absorption will affect the tissues by not providing the nutrients.
• Increased tissue pressure can damage the cells.
June 2013
Regulation of fluid and electrolytes 11
Causes of Oedema
• Intracellular:-
– Depression of Metabolism or lack of nutrients resulting in failure of sodium pump.
– Inflammation resulting from increased cell membrane permeability
• Extracellular: increased capillary filtration [pitting] or lymphatic failure [non pitting]
June 2013
Regulation of fluid and electrolytes 12
Increased Tissue Fluid
• Increased capillary filtration coefficient [capillary permiability].
• Increased capillary hydrostatic pressure.
• Decreased plasma colloid osmotic pressure.
June 2013
Regulation of fluid and electrolytes 13
Increased capillary pressure• Excessive kidney retention of salt and water
– Acute or chronic kidney failure, Mineralocorticoid excess
• High venous pressure and venous constriction
– Heart failure, Venous obstruction, Failure of venous pumps
• Paralysis of muscles
– Immobilization of parts of the body, Failure of venous valves
• Decreased arteriolar resistance
– Excessive body heat, Insufficiency of sympathetic nervous system
June 2013
Regulation of fluid and electrolytes 14
Decreased plasma proteins
• Loss of proteins in urine (nephrotic syndrome)
• Loss of protein from denuded skin areas
– Burns
– Wounds
• Failure to produce proteins
– Liver disease (e.g., cirrhosis)
– Serious protein or caloric malnutritionJune 2013
Regulation of fluid and electrolytes 15
Increased capillary permeability
• Immune reactions that cause release of histamine and other immune products
• Toxins
• Bacterial infections
• Vitamin deficiency, especially vitamin C
• Prolonged ischemia
• Burns
June 2013
Regulation of fluid and electrolytes 16
Blockage of lymph return
• Cancer
• Infections (e.g., filaria nematodes)
• Surgery
• Congenital absence or abnormality of lymphatic vessels
June 2013
Regulation of fluid and electrolytes 17
Dehydration
• Filtration pressure decreased
• Tissue fluid formation reduced
• Tissue nutrition impaired
• Metabolites accumulate
• If prolonged, tissue damage
June 2013
Regulation of fluid and electrolytes 18
Causes of Dehydration
• Not drinking water- no drinking water or ? no time to drink
• Haemorrhage- loss of blood
• Burns- loss of plasma
• Excessive sweating- loss of hypotonic fluid
• Diarrhoea, vomiting- loss of sodium and potassium with water
• Excessive urine flow-
– Lack of ADH, Diabetes MellitusJune 2013