BIO 142 lecture: Acid-base balance

3. Explain the process of intracellular and extracellular buffering mechanisms.

(1) Amino acids of proteins can accept and donate H+, so proteins can help maintain pH balance if the pH increases or decreases. (2) Proteins in the intracellular fluid, the plasma, and interstitial fluid can function as buffers. (3) Hemoglobin buffering system: RBCs uptake CO2 from the plasma. The CO2 then combines with water to produce carbonic acid, which is facilitated by carbonic anhydrase. Ultimately, the carbonic acid dissociates into H+ and HCO3-. The H+ is then buffered by hemoglobin.

9. State three causes of metabolic acidosis resulting from an alteration of H+ levels.

(1) increased lactic acid production (2) ketoacidosis (starvation and diabetes mellitus) (3) Impaired ability of the kidney to excrete H+ (glomerulonephritis)

2. List the ways the body attempts to maintain a normal blood pH range.

-Buffers -Respiratory center -Adjustments in acid excretion by the kidney

6. Explain the role of the carbonic acid-bicarbonate buffering system when body fluids are alkaline.

-Increase in alkalinity (rare) = CO2 combines with H2O to ultimately produce H+ ions

5. Explain the role of the carbonic acid-bicarbonate buffering system when body fluids are acidic.

-The carbonic acid-bicarbonate system prevents changes in pH caused by organic acids and fixed acids in the ECF.

14. Explain the physiological mechanisms (buffers, respiration, renal) that attempt to compensate for metabolic alkalosis.

-The increase in pH inhibits the respiratory center (respiratory compensation). -Renal reabsorption of HCO3- by the nephron is inhibited, which results in increased excretion of HCO3-

7. Explain the role of the respiratory system in maintaining blood pH within a normal range.

1. The lungs are the second line of defense against acid-base disorders. 2. increased PCO2 = blood becomes acidic (decreased pH) 3. decreased PCO2= blood becomes basic (increased pH) 4. Rate of pulmonary ventilation is the main determinate of PCO2 5. Remember that central chemoreceptors and peripheral chemoreceptors can detect changes in plasma PCO2 and H+ concentration and influence the respiratory center accordingly. a) During metabolic acidosis (increase H+, decreased pH), pulmonary ventilation rate increases b) During metabolic alkalosis (decreased H+, increased pH), pulmonary ventilation rate decreases.

8. Explain the role of kidney physiology in maintaining blood pH within a normal range.

1. The third line of defense is the kidneys. 2. Acidosis (increase H+ or PCO2) a) The nephron secretes H+ b) The entire amount of filtered HCO3- is reabsorbed from the lumen of the renal tubule back into the blood. 3. Alkalosis (decrease H+ or PCO2) a) Secretion of H+ by the nephron is inhibited b) HCO3- reabsorption is reduced causing more HCO3- to remain in the lumen of the renal and ultimately be excreted as a component of the urine.

22. State the normal ranges of blood pH, CO2, and HCO3-.

1. pH: The ideal pH for blood is 7.4, but the acceptable range is 7.357.45 2. CO2: 35-45 mm/Hg 3. PO2: 80-100 mm/Hg 4. O2 saturation: 95-100% 5. HCO3-: 22-26 mEq/L

17. Contrast acute respiratory acidosis with chronic respiratory acidosis.

3. Acute respiratory acidosis a) If the respiratory center is incapable of normal function, CO2 will build up rapidly in the plasma causing the plasma to become acidic. b) In acute respiratory acidosis the there is little time for the kidney to compensate, so this is a life-threatening situation. 4. Chronic respiratory acidosis a) Intracellular buffers absorb H+ b) Kidneys increase the secretion of H+ c) Kidneys increase reabsorption HCO3-

21. Explain the physiological mechanisms (buffers, respiratory, renal) that attempt to compensate for respiratory alkalosis.

3. Buffering is primarily intracellular 4. HCO3- reabsorption is inhibited 5. H+ secretion is decreased a) substances that prevent significant changes in pH and are important for many small adjustments in H+ ion concentration b) If H+ ion concentration is too high the buffer combines with H+ ions to bring the ph back to normal. c) If H+ ion concentration is too low the buffer releases H+ ions to lower the pH. d) Important blood buffer system (1) Rise in pH: H2CO3 HCO3- + H+ (2) Low pH: H+ HCO3- H2CO3

1. State the normal pH range of blood.

7.35-7.45

23. Interpret arterial blood gas data and determine if the patient from which the sample was taken has metabolic acidosis (compensated or uncompensated), metabolic alkalosis (compensated or uncompensated), respiratory acidosis (compensated or uncompensated), respiratory alkalosis (compensated or uncompensated), or is normal.

Basics of interpretation 1. Determine if the pH is acidic or alkaline. 2. Determine CO2 is normal, elevated (acidic), or decreased (alkaline). 3. Determine if the HCO3- is normal, elevated (alkaline), or decreased (acidic). 4. Determine the relationship between pH and CO2 and HCO3-. An easy way to remember the relationship is: Respiratory Opposite Metabolic Equal (ROME). a) If pH is acidic (decreased) and CO2 is acidic (increased), then the condition is respiratory acidosis (respiratory opposite). (1) Respiratory acidosis results from the inability of the body to expel CO2. (2) Compensation results from the kidney secreting H+ and conserving HCO3-. If compensation has occurred, then the pH will be between 7.35 and .39 and HCO3- levels will be increased. b) If pH is acidic (decreased) and HCO3- is acidic (decreased), then the condition is metabolic acidosis (metabolic equal). (1) Metabolic acidosis results from increased production of H+, impaired loss of H+ by kidney, or loss of HCO3-. (2) Compensation results from the respiratory system increasing pulmonary ventilation. If compensation has occurred, then the pH will be between 7.35 and 7.39 and CO2 levels will be decreased. c) If pH is alkaline (increased) and CO2 is alkaline (decreased), then the condition is respiratory alkalosis (respiratory opposite). (1) Respiratory alkalosis results from increased pulmonary ventilation. (2) Compensation by the kidney attempts to retain H+ and secrete HCO3-. If compensation has occurred, then the pH will be between 7.41 and 7.45 and the HCO3- levels will be decreased. d) If the pH is alkaline (increased) and HCO3- is also alkaline (increased), then the condition is metabolic alkalosis. (1) Metabolic acidosis results in the increased production and release of HCO3- by the body (parietal cells of stomach). (2) Compensation by the respiratory system results in decreased pulmonary ventilation. If compensation has occurred, then the pH will be between 7.41 and 7.45 and CO2levels will be increased. The kidneys will also excrete HCO3- and retain H+.

4. Write the carbonic acid-bicarbonate reaction.

CO2 + H2O H2CO3 H+ + HCO3-

16. Explain the relationship between ventilation, gas diffusion, and pulmonary blood flow in the development of respiratory acidosis.

Decreased gas exchange across the respiratory membrane leads to respiratory acidosis. a) Inadequate ventilation (hypoventilation) results in hypercapnia (CNS injury or drug induced depression of the respiratory center) b) Impaired gas diffusion or inadequate blood flow to the lungs (pulmonary edema, pneumonia, CHF)

12. Explain the role of HCO3- in the development of metabolic alkalosis.

HCO3- concentration increases, which causes the pH to increase.

20. Explain the relationship between an increased respiratory rate and respiratory alkalosis.

It results from increased gas exchange across the respiratory membrane in the lungs. a) Increased ventilation from stimulation of respiratory centers (Drugs or CNS disorders) b) Hyperventilation due to fear of anxiety

10. State one cause of metabolic acidosis resulting from an alteration of HCO3- levels.

Metabolic acidosis results from an increased H+ concentration and a low plasma HCO3- concentration, which lowers the pH -A low HCO3- concentration can result from excessive diarrhea, which lowers the pH. (1) increased lactic acid production (2) ketoacidosis (starvation and diabetes mellitus) (3) Impaired ability of the kidney to excrete H+ (glomerulonephritis

15. Explain the role of CO2 in the development of respiratory acidosis.

Respiratory acidosis results from an elevated PCO2, which lowers the plasma pH.

19. Explain the role of CO2 in the development of respiratory alkalosis.

Respiratory acidosis results from decreased plasma CO2 (hypocapnia), which increases plasma pH.

18. Explain the physiological mechanisms (buffers, respiratory, renal) that attempt to compensate for respiratory acidosis.

a) Intracellular buffers absorb H+ b) Kidneys increase the secretion of H+ c) Kidneys increase reabsorption HCO3-

13. State two causes of metabolic alkalosis

a) administration of excessive antacids b) excessive vomiting

11. Explain the physiological mechanisms (buffers, respiration, renal) that attempt to compensate for metabolic acidosis.

a) buffering of H+ will occur in both extracellular fluid and intracellular fluid b) decrease in pH stimulates the respiratory center to increase pulmonary ventilation (respiratory compensation) c) renal excretion of H+ is increased (renal compensation)