Chapter 27

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

2. 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 Sources of water Ingestion Cellular metabolism Routes of water loss Urine Evaporation Perspiration Respiratory passages Feces Regulation of Water Content

3. Extracellular Fluid Osmolality • 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

4. Hormonal Regulation of Blood Osmolality

5. 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 leads to increased pressure in glomerulus leading to increased filtration and increased urine output. • Renin-angiotensin-aldosterone • Atrial natriuretic hormone (ANH) • Antidiuretic hormone (ADH)

6. Increase in Blood Volume

7. Decrease in Blood Volume

8. Regulation of ECF Volume

9. Electrolytes Molecules or ions with an electrical charge Ingestion adds electrolytes to body Kidneys, liver, skin, 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 {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+ Regulation of Electrolytes in ECF

10. 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: abnormally high levels of potassium in extracellular fluid Hypokalemia: abnormally low levels of potassium in extracellular fluid. Regulation of Chloride, Potassium, Magnesium Ions

11. Potassium Ion Regulation in ECF

12. 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

13. Regulation of Calcium Ions

14. Regulation of Blood Magnesium

15. 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 it When H+ removed, buffer replaces it Types of buffer systems Carbonic acid/bicarbonate Protein Phosphate Acids and Basesand Buffers

16. Comparison of Strong and Weak Acids

17. 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; if pH falls, distal tubule increases H+ secretion into the urine

18. Increase in Blood pH

19. Decrease in Blood pH

20. Respiratory Regulation ofAcid-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

21. Respiratory Regulation ofAcid-Base Balance

22. Kidney Regulation of Acid-Base Balance

23. 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.