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Water, Electrolytes, and Acid-Base Balance

This comprehensive guide covers the intricate balance of water, electrolytes, and acid-base levels within the body's fluid compartments. Learn about intracellular and extracellular fluids, regulatory mechanisms, hormonal influences, and the role of key electrolytes like sodium, potassium, and calcium. Explore the processes of osmosis, hormonal regulation, and buffering systems that maintain homeostasis. Discover how the kidneys, lungs, and other organs work synergistically to manage fluid volume and electrolyte concentrations while regulating acid-base balance.

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Water, Electrolytes, and Acid-Base Balance

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  1. Water, Electrolytes, and Acid-Base Balance

  2. Body Fluids • Intracellular • All fluids inside cells of body • About 40% of total body weight • Extracellular • All fluids outside cells • About 20% of total body weight • Subcompartments • Interstitial fluid and plasma; lymph, CSF, synovial fluid

  3. Body Fluid Compartments

  4. Content regulated so total volume of water in body remains constant Kidneys primary regulator of water excretion Regulation processes Osmosis Osmolality Baroreceptors Learned behavior Sources of water Ingestion Cellular metabolism Routes of water loss Urine Evaporation Perspiration Respiratory passages Feces Water Content Regulation

  5. Osmolality Adding or removing water from a solution changes this Increased osmolality Triggers thirst and ADH secretion Decreased osmolality Inhibits thirst and ADH secretion Extracellular Fluid Osmolality

  6. Hormonal Regulation of Blood Osmolality

  7. Mechanisms Neural Renin-angiotensin-aldosterone Atrial natriuretic hormone (ANH) Antidiuretic hormone (ADH) Increased ECF results in Decreased aldosterone secretion Increased ANH secretion Decreased ADH secretion Decreased sympathetic stimulation Decreased ECF results in Increased aldosterone secretion Decreased ANH secretion Increased ADH secretion Increased sympathetic stimulation Regulation of ECF Volume

  8. Hormonal Regulation of Blood Volume

  9. Hormonal Regulation of Blood Volume

  10. Regulation of ECF Volume

  11. Regulation of ICF and ECF

  12. Electrolytes Molecules or ions with an electrical charge Water ingestion adds electrolytes to body Kidneys, liver, skin, lungs remove from body Concentration changes only when growing, gaining or losing weight Na+ Ions Dominant ECF cations Responsible for 90-95% of osmotic pressure Regulation of Na+ ions Kidneys major route of excretion Small quantities lost in sweat Terms Hypernatremia Hyponatremia Regulation of Electrolytes in ECF

  13. Mechanisms Regulating Blood Sodium

  14. Mechanisms Regulating Blood Sodium

  15. Abnormal Plasma Levels of Sodium Ions

  16. Chloride ions Predominant anions in ECF Magnesium ions Capacity of kidney to reabsorb is limited Excess lost in urine Decreased extracellular magnesium results in greater degree of reabsorption Potassium ions Maintained in narrow range Affect resting membrane potentials Aldosterone increases amount secreted Terms Hyperkalemia Hypokalemia Regulation of Chloride, Potassium, Magnesium Ions

  17. Potassium Ion Regulation in ECF

  18. Abnormal Concentration of Potassium Ions

  19. Abnormal Plasma Levels of Magnesium Ions

  20. Regulation of Blood Magnesium

  21. Regulated within narrow range Elevated extracellular levels prevent membrane depolarization Decreased levels lead to spontaneous action potential generation Terms Hypocalcemia Hypercalcemia PTH increases Ca2+ extracellular levels and decreases extracellular phosphate levels Vitamin D stimulates Ca2+ uptake in intestines Calcitonin decreases extracellular Ca2+ levels Regulation of Calcium Ions

  22. Regulation of Calcium Ions

  23. Regulation of Phosphate Ions • Under normal conditions, reabsorption of phosphate occurs at maximum rate in the nephron • An increase in plasma phosphate increases amount of phosphate in nephron beyond that which can be reabsorbed; excess is lost in urine

  24. Regulation of Blood Phosphate

  25. Acids Release H+ into solution Bases Remove H+ from solution Acids and bases Grouped as strong or weak Buffers: Resist changes in pH When H+ added, buffer removes When H+ removed, buffer replaces Types of buffer systems Carbonic acid/bicarbonate Protein Phosphate Acids and Basesand Buffers

  26. Regulation of Acid-Base Balance

  27. Regulation of Acid-Base Balance

  28. Buffer Systems

  29. Respiratory Regulation ofAcid-Base Balance • Respiratory regulation of pH is achieved through carbonic acid/bicarbonate buffer system • As carbon dioxide levels increase, pH decreases • As carbon dioxide levels decrease, pH increases • Carbon dioxide levels and pH affect respiratory centers • Hypoventilation increases blood carbon dioxide levels • Hyperventilation decreases blood carbon dioxide levels

  30. Respiratory Regulation ofAcid-Base Balance

  31. Renal Regulation of Acid-Base Balance • Secretion of H+ into filtrate and reabsorption of HCO3- into ECF cause extracellular pH to increase • HCO3- in filtrate reabsorbed • Rate of H+ secretion increases as body fluid pH decreases or as aldosterone levels increase • Secretion of H+ inhibited when urine pH falls below 4.5

  32. Kidney Regulation of Acid-Base Balance

  33. Hydrogen Ion Buffering

  34. Acidosis and Alkalosis • Acidosis: pH body fluids below 7.35 • Respiratory: Caused by inadequate ventilation • Metabolic: Results from all conditions other than respiratory that decrease pH • Alkalosis: pH body fluids above 7.45 • Respiratory: Caused by hyperventilation • Metabolic: Results from all conditions other than respiratory that increase pH • Compensatory mechanisms

  35. Acidosis and Alkalosis

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