1. Water, Electrolytes, and
Acid-Base Balance

2. 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

3. Body Fluid Compartments

4. 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

5. 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

6. Hormonal Regulation of Blood Osmolality

7. 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)

8. Hormonal Regulation of Blood Volume

9. Hormonal Regulation of Blood Volume

10. Regulation of ECF Volume

11. Regulation of ICF and ECF

12. 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

13. Mechanisms Regulating Blood Sodium

14. Mechanisms Regulating Blood Sodium

15. Abnormal Plasma Levels of Sodium Ions

16. 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

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. 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

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 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

26. Regulation of Acid-Base Balance

27. Regulation of Acid-Base Balance

28. Buffer Systems

29. 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

30. Respiratory Regulation of Acid-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