1. 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.

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

3. 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-

4. Body Fluid Compartments

5. 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

6. 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

7. Hormonal Regulation of Blood Osmolality

8. 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)

9. Increase in Blood Volume

10. Decrease in Blood Volume

11. Regulation of ECF Volume

12. 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

13. Regulation of ICF and ECF

17. 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

18. Potassium Ion Regulation in ECF

20. 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

21. Regulation of Calcium Ions

23. Regulation of Blood Magnesium

25. 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)

26. Regulation of Blood Phosphate

28. 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

29. Comparison of Strong and Weak Acids

30. 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

32. Increase in Blood pH

33. Decrease in Blood pH

34. 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

35. Respiratory Regulation of Acid-Base Balance

36. 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

37. Kidney Regulation of Acid-Base Balance

38. Hydrogen Ion Buffering

39. 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