Water, Electrolytes, and Acid-Base Balance

Body Fluids Intracellular Extracellular 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

Body Fluid Compartments

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

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

Hormonal Regulation of Blood Osmolality

Regulation of ECF Volume 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 Mechanisms Neural Renin-angiotensin-aldosterone Atrial natriuretic hormone (ANH) Antidiuretic hormone (ADH)

Hormonal Regulation of Blood Volume

Hormonal Regulation of Blood Volume

Regulation of ECF Volume

Regulation of ICF and ECF

Regulation of Electrolytes in ECF 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 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

Mechanisms Regulating Blood Sodium

Mechanisms Regulating Blood Sodium

Abnormal Plasma Levels of Sodium Ions

Regulation of Chloride, Potassium, Magnesium Ions Potassium ions Maintained in narrow range Affect resting membrane potentials Aldosterone increases amount secreted Terms Hyperkalemia Hypokalemia 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 Ion Regulation in ECF

Abnormal Concentration of Potassium Ions

Abnormal Plasma Levels of Magnesium Ions

Regulation of Blood Magnesium

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

Regulation of Calcium Ions

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

Regulation of Blood Phosphate

Acids and Bases and Buffers 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 Release H+ into solution Bases Remove H+ from solution Acids and bases Grouped as strong or weak

Regulation of Acid-Base Balance

Regulation of Acid-Base Balance

Buffer Systems

Respiratory Regulation of Acid-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

Respiratory Regulation of Acid-Base Balance

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

Kidney Regulation of Acid-Base Balance

Hydrogen Ion Buffering

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

Acidosis and Alkalosis