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Generally how is acid-base balance maintained in the body?

maintained by controlling the H+ concentration of body fluids, especially extracellular fluid.


Why is [H+] essential for homeostasis?

  • Proteins (including enzymes) 3-D structure sensitive to pH changes
    • pH declines 1 unit = Sodium-potassium pump decreases by half
    • pH declines 0.1 unit = Phosphofructo-kinase activity decreases by 90%


diet high in proteins tends to acidify or alkanize the blood



what is normal pH in blood?

7.35 - 7.45



  1. Acidemia 
  2. Acidosis

  1. Acidemia- increase in acidity of blood
  2. Acidosis- increase in acidity of tissues


  1. what pH is acidemia?
  2. alkalemia

  1. Acidemia = pH < 7.35
  2. Alkalemia = pH > 7.45



  1. Alkalemia
  2. Alkalosis

  1. Alkalemia- increase in basicity in blood
  2. Alkalosis- increase in basicity in tissues


what will happen in acidosis generally?

Acidosis- Principal effect is depression of the central nervous system through depression of synaptic transmission. -> Coma


what will happen in alkalosis generally?

Alkalosis- Overexcitability of the central nervous system through facilitation of synaptic transmission. -> Seizures


what are 3 major mechanisms to regulate pH and generally how much time for each

  1. Buffer systems- Seconds

  2. Exhalation of CO2 -Minutes to hours

  3. Kidney excretion of H+ - Days


  1. what are the 3 buffer systems?
  2. what do they generally do?

  1. Protein buffer system,
    • carbonic acid-bicarbonate buffer system,
    • phosphate buffer system
  2. Prevent rapid, drastic changes in pH


  1. what does the protein buffer system do?
  2. Where is the protein buffer system found?

  1. Change either strong acid or base into weaker one
  2. Abundant in intracellular fluids and in plasma


  1. What is a good protein buffer in RBCs?
  2. plasma?

  1. hemoglobin very good at buffering H+ in RBCs
  2. albumin is main plasma protein buffer


regarding the protein buffer system

Amino acids contains at least one carboxyl group (-COOH) and at least one amino group (-NH2)

  • what will each group do?


  • carboxyl group acts like an acid and releases H+
  • amino group acts like a base and combines with H+


Regarding the protein buffer system

  • What acts as a buffer in blood by picking up CO2 or H+



  1. what does the carbonic acid-bicarbonate buffer system do?



  1. Acts as extracellular & intracellular buffer system
    • bicarbonate ion (HCO3-) can act as a weak base
      • holds excess H+
    • carbonic acid (H2CO3) can act as weak acid
      • dissociates into H+ ions


Regarding the carbonic acid-bicarbonate buffer system

  1. At a pH of 7.4, bicarbonate ion concentration is about __ times that of carbonic acid
  2. What is a limitation of this buffer system


  1. 20 times
  2. Cannot protect against pH changes due to respiratory problems


  1. What does the phosphate buffer system do? (what 2 components)
  2. where is it located?

  1. Dihydrogen phosphate ion acts as a weak acid that can buffer a strong base
    • Monohydrogen phosphate acts a weak base by buffering the H+ released by a strong acid
  2. Most important intracellularly, but also acts to buffer acids in the urine




  1. CO2 is an acid or base?
  2. what is CO2 a result of?

  1. Volatile acid – CO2
  2. Result of carbohydrate and fat metabolism


  1. If PaCO2 is high what is the respiratory system currently doing
  2. low?


  1. high- Hypoventilation
  2. low- Hyperventilation


How does the animal compensate if pH is low = Acidemia?

  1. Exhalation of Carbon Dioxide and
  2. Renal Excretion of H+ and Reabsorption of HCO3


How does the animal's respiratory system compensate if pH is low (acidemia)

An increase in the rate and depth of breathing causes more carbon dioxide to be exhaled, thereby increasing pH.


What are the first 2 steps of figuring out an acid-base problem

  1. Note whether the pH is increased or decreased relative to the normal pH range.
  2. Decide which value of PCO2 or HCO3- was the primary cause of the pH change. (increased or decreased)


  1. Respiratory acidosis and alkalosis are disorders involving changes in 
  2. Metabolic acidosis and alkalosis are disorders due to changes in 

  1. PCO2 in blood
  2. HCO3- in blood


What are steps 3 and 4 for figuring out acid-base problems

3. Specify the primary problem as respiratory or metabolic.

4. Look at the non-causative (compensatory/secondary) value and determine if it is compensating for the primary problem.


  • Respiratory System
  • Urinary System


  1. PCO2 > 45 mm Hg = ?
  2. PCO2 < 35 mm Hg = ?

  1. PCO2 > 45 mm Hg = Respiratory Acidosis (increased PCO2)
  2. PCO2 < 35 mm Hg = Respiratory Alkalosis (decreased PCO2)


  1. HCO3- < 22mEQ/L = ?
  2. HCO3- > 26mEQ/L = ?

  1. HCO3- < 22mEQ/L = Metabolic Acidosis
  2. HCO3- > 26mEQ/L = Metabolic Alkalosis


Primary causes of hypoventilation: (4)

  1. Anesthesia, opioids
  2. Cervical cord trauma
  3. Airway obstruction
  4. Injury to the brainstem and respiratory centers


FYI, treatments of respiratory acidosis


  • Correct primary problem
  • IV administration of bicarbonate (HCO3-)
  • Ventilation therapy to increase exhalation of CO2