Regulation of Fluid and Electrolyte Balance

1. Regulation of Fluid and Electrolyte Balance Prof. K. Sivapalan

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. 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. 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 Regulation of fluid and electrolytes

5. Effects of Drinking Water 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. 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. 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. 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. 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. 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] Regulation of fluid and electrolytes

12. Increased Tissue Fluid • Increased capillary filtration coefficient [capillary permiability]. • Increased capillary hydrostatic pressure. • Decreased plasma colloid osmotic pressure. 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 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 malnutrition Regulation of fluid and electrolytes

15. Increased capillary permeability • Immune reactions that cause release of histamine and other immune products • Toxins • Bacterial infections • Vitamindeficiency, especiallyvitamin C • Prolonged ischemia • Burns Regulation of fluid and electrolytes

16. Blockage of lymph return • Cancer • Infections (e.g., filaria nematodes) • Surgery • Congenital absence or abnormality of lymphatic vessels Regulation of fluid and electrolytes

17. Dehydration • Filtration pressure decreased • Tissue fluid formation reduced • Tissue nutrition impaired • Metabolites accumulate • If prolonged, tissue damage 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 Mellitus Regulation of fluid and electrolytes