Chapter 27 Lecture Outline* Rod R. Seeley Idaho State University Trent D. Stephens Idaho State University Philip Tate Phoenix College *See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Water, Electrolytes, and Chapter 27 Water, Electrolytes, and Acid-Base Balance

Body Fluids Intracellular fluid compartment All fluids inside cells of body About 40% of total body weight Extracellular fluid compartment All fluids outside cells About 20% of total body weight Subcompartments Interstitial fluid and plasma; lymph, CSF, synovial fluid Primary intracellular ions, interstitial fluid ions, and plasma ions Intracellular cation = K+ Interstitial fluid cation = Na+ Plasma cation = Na+ Intracellular anion = Phosphate Interstitial fluid = Cl- Plasma anion = Cl-

Body Fluid Compartments

Regulation of Water Content 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 are primary regulators of water excretion Regulation processes Osmosis Osmolality Baroreceptors Learned behavior

Extracellular Fluid Osmolality Measure of water vs. solute concentration; the higher the solute concentration, the higher the osmolality Adding or removing water from a solution changes osmolality Increased osmolality: triggers thirst and ADH secretion Decreased osmolality: inhibits thirst and ADH secretion

Hormonal Regulation of Blood Osmolality

Regulation of ECF Volume ECF can increase or decrease even if osmolality of extracellular fluid is maintained Carotid sinus and aortic arch baroreceptors monitor blood pressure, juxtaglomerular apparatuses monitor pressure changes, receptors in walls of atria and large vessels respond to small changes in BP These receptors activate these mechanisms Neural: increase in BP recognized by baroreceptors. Decreased sympathetic stimulation of afferent arteriole leads to increased pressure in glomerulus leading to increased filtration and increased urine output. Renin-angiotensin-aldosterone Atrial natriuretic hormone (ANH) Antidiuretic hormone (ADH)

Increase in Blood Volume

Decrease in Blood Volume

Regulation of ECF Volume

Regulation of Electrolytes in ECF Regulation of Na+ ions Kidneys major route of excretion Small quantities lost in sweat {sweat = (in decreasing amounts) water, Na+, urea, Cl-K+, NH3}. Insensible perspiration is water evaporating from skin. Sensible perspiration is secreted by the sweat glands. Contains solutes Terms Hypernatremia: elevated plasma Na+ Hyponatremia: decreased Na+ Electrolytes Molecules or ions with an electrical charge 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 ICF and ECF

Regulation of Chloride, Potassium, Magnesium Ions Potassium ions Maintained in narrow range Affect resting membrane potentials Aldosterone increases amount secreted Terms Hyperkalemia: abnormally high levels of potassium in extracellular fluid Hypokalemia: abnormally low levels of potassium in extracellular fluid. 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

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 Blood Magnesium

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 Hypophosphatemia: reduced absorption from intestine due to vitamin D deficiency or alcohol abuse. Hyperphosphatemia: renal failure, chemotherapy, hyperparathyroidism (secondary to elevated plasma calcium levels)

Regulation of Blood Phosphate

Acids and Bases and Buffers Buffers: Resist changes in pH When H+ added, buffer removes it When H+ removed, buffer replaces it 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

Comparison of Strong and Weak Acids

Regulation of Acid/Base Balance Buffers: if pH rises, buffers bind H+; if pH falls, buffers release H+ Protein buffer: Intracellular and plasma proteins absorb H+. Provide ¾ of buffering in body. E.g., hemoglobin. Bicarbonate buffering system: Important in plasma Phosphate buffer system: important as an intracellular buffer Respiratory center: if pH rises, respiratory rate decreases; if pH falls, respiratory rate increases Kidneys: if pH rises, distal tubule decreases H+ secretion into the urine and decreases HCO3- absorption into the blood (more H2CO3 will dissociate into H+ and HCO3-); if pH falls, distal tubule increases H+ secretion into the urine and increases HCO3- absorption into the blood

Increase in Blood pH

Decrease in Blood pH

Respiratory Regulation of Acid-Base Balance 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- reduced elimination of CO2, asthma, damage to respiratory center in brain, emphysema. Metabolic: Results from all conditions other than respiratory that decrease pH- diarrhea, vomiting, ingesting overdose of aspirin, untreated diabetes mellitus, anaerobic respiration Alkalosis: pH body fluids above 7.45 Respiratory: Caused by hyperventilation, high altitude (reduced partial pressure of O2 Metabolic: Results from all conditions other than respiratory that increase pH- severe vomiting, too much aldosterone, ingestion of substances like bicarbonate of soda. Compensatory mechanisms