Physio L36- Acid-Base Balance

  1. Acids
    • pH 0-6
    • Acids are AH- acids dissociate into A- and H+
    • AH <-> A-+H+
    • Strong Acids, like HCl in the stomach, completely dissociate
    • Weak acids, like H2CO3 carbonic acid, partially dissociate
    • H++HCO3- -> H2CO3
    • Free H++Free anion
    • H+ increases...more acidic
    • H+ decreases...less acidic
  2. Bases
    • pH 8-14
    • Bases, B, can bind H+ to become BH+
    • The only significant physiological base is ammonia, NH3 becomes NH4
    • Ammonia, buffers renal filtrate, allowing more H+ excretion
    • H2O-> OH-+H+
  3. pH
    • Measure of H+ in a solution
    • pH=-log[H+], increases in H+ cause decreases in pH
    • The average blood pH is 7.40, average cell pH is about 7.0
    • Blood pH below 7.35 is acidosis, blood pH about 7.45 is alkalosis
    • Acidosis is far more common than alkalosis
    • cells will have bigger pH shifts than blood
  4. Acidosis Effects
    • Depresses the neurons, especially in the CNS
    • Alkalosis makes neurons hyper-excitable
    • In general decreases enzyme activity, but a few increase
    • Causes increased H+ excretion, and therefore decreased K+ excretion: Increased K+ causes cardiac and neural problems
  5. Sources of H+
    • Small amounts in food, such as citric acid
    • Most generated in the body: carbonic acid from CO2, sulfur and phosphoric acids from proteins, metabolic acids such as lactic acids
  6. Control of H+
    • H+ is controlled in 3 ways:
    • Chemical Buffering
    • Respiratory Control of CO2
    • Renal Control of H+ Excretion
    • Buffers----(addition of 3 HCl to unbuffered solution)---> 3 free H+ present
  7. Buffers
    • Different buffers work in different places
    • Buffers work by binding H+ from the solution and from pH
    • First line of H+ defense
  8. Extracellular Buffering
    • Bicarbonate is the most important ECF buffer
    • HCO3- bind H+ to form H2CO3, which dissociates to CO2+H2O
    • Hemoglobin in RBCs buffers H+ produced by CO2 increases in venous blood
  9. Intracellular Buffering
    • Proteins in cells bind H+ in ICF
    • In some cells, especially muscle cells, phosphate helps buffer ICF
  10. Urine buffering
    • Phosphate and bicarbonate are dissociated acids that buffer renal filtrate
    • Ammonia is a base that also buffers renal filtrate
  11. Respiratory Control of H+
    • Second line of H+ defense. Works with non-respiratory sources of H+
    • Increased H+ or increased CO2, increases depth and frequency of respiration- this reduces CO2 in blood, reducing H+ back toward normal
  12. Kidney Control of H+
    • Third line of H+ defense
    • Removes H+ from any non-renal sources in the body
  13. H+ Excretion
    • H+ ion pumps in the renal tubules secrete H+ into the filtrate
    • Urine pH is normally 6.0 but can also be lower
  14. Acid-Base Imbalances
    • Pathological changes in the control of H+ results in pH changes
    • These can be compensated by the respiratory and renal systems, if not of respiratory or renal origin
    • A system cannot compensate for its own problems: renal problems require respiratory compensation; respiratory problems require renal compensation
  15. Respiratory Acidosis
    Abnormal CO2 retention from hypoventilation
  16. Respiratory Alkalosis
    • Decreased CO2 by hyperventilation
    • Fear/ anxiety, aspirin poisoning, conscious breathing
    • Decreased H+ secretion removal condition
  17. Metabolic Acidosis
    • *cancer with tumors (more energy)
    • Most common acid base disorder
    • Severe diarrhea, loss of bicarbonate
    • Excess H+ production during fat use in diabetics
    • Exercise leading to lactate and H+ production (bad breath)
    • Kidney failure, cannot excrete H+ or conserve HCO3-
  18. Metabolic Alkalosis
    • Decrease in H+ for non-respiratory reasons
    • Vomiting loses H+ in vomitus
    • Excess bicarbonate ingestion
    • Decrease respiratory rate and retain H+ in kidneys in compensate
    • H+ retention increases K+ loss
Card Set
Physio L36- Acid-Base Balance
MSU Physio