Respiration Lecture 11: Resp. Acid-Base Balance Flashcards
Base
ion or molecule that can accept a H+ atom. A- in HH equation
Acid
molecules containing H+ atoms that can be released into solutions. HA in HH equation.
When is buffer system most resistant to changes in H+?
When pH = pK
Normal extracellular pH range
7.35-7.45
3 main mechanisms to keep pH within normal limits
1) extracellular buffering (don’t actually remove H+ from system)
2) adjustments to blood PCO2 by altering the ventilatory capacity of the lungs (<—THE MAIN METHOD…KNOW!)
3) adjustments to renal acid excretion or base reabsorption
Acidemia
acidic blood (high H+ conc.)
Alkalemia
alkaline blood (low H+ conc.)
where is H ion state measured?
receptors in CSF
weak acid or base
acid or base that incompletely dissociates. (pK is such that it doesn’t completely dissociate)
buffer
reduces changes in pH resulting from the addition of strong acids or bases
What is greatest source of H+?
CO2 (via oxidation of glucose and fatty acids during metabolism)
CO2 is an example of what type of acid?
volatile acid
Non-volatile acids that are sources of H+ in metabolism
sulfuric, phosphoric, hydrochloric, and lactic acids
The #1 blood buffer
Bicarbonate ***** Most important because the buffered H+ ion it can carry can be removed by both the renal and respiratory systems
Other blood buffers besides bicarbonate
phosphate, proteins
Henderson-Hasselbalch Equation
HA H+ + A- and pH = pKa + log [A-]/[HA] DNK
how many pH units around pK can buffer act?
+/- 1 pH unit
Buffer strength is directly proportional to ?
concentration of paired buffer components
Non-bicarbonate buffer systems
Phosphate buffer system
Protein buffer system
Bicarbonate buffer system **
utilizes carbonic anhydrase reaction to maintain blood pH. carbon dioxide (CO2) combines with water to form carbonic acid (H2CO3), which in turn rapidly dissociates to form hydrogen ions and bicarbonate (HCO3- ) as shown in the reactions below. The carbon dioxide - carbonic acid equilibrium is catalyzed by the enzyme carbonic anhydrase; the carbonic acid - bicarbonate equilibrium is simple proton dissociation/association and needs no catalyst. An OPEN SYSTEM via elimination of CO2 and H+ to the environment
Carbonic anhydrase reaction
CO2 + H2O H2CO3 H+ + HCO3-
CO2 = acid (proton donor) HCO3 = base (proton acceptor) H+ = free proton responsible for setting pH
If alveolar pressure decreases due to hypoventilation, what happens to pH?****
increase in PCO2, so pH decreases (increase in H+)
Phosphate buffer system reaction
H2PO4 H+ + HPO4
What happens to acidity of Hb as O2 leaves?
Decreases
deoxyhemoglobin
Hb that is desaturated of O2
Hb protein buffer system
Hb becomes more acidic when it binds O2, allowing less CO2 to be transferred as bicarbonate and vice versa.
Which two organs regulate the bicarbonate buffer system?
lungs and kidneys
Only way to ELIMINATE H+ ?
via blown off CO2 or renal excretion
most important blood borne protein buffer
Hb
protein with highest conc. in blood
Hb
Is Hb classified as extracellular or intracellular?
extracellular
Where is phosphate buffer system strongest and why?
kidney. Env. is more acidic and phosphate is higher
How does bicarbonate buffer system compensate for its low pK?
By being an open system
organ that releases the largest amount of acid
resp. system
primary body systems that regulate H+
respiratory, renal, and gastrointestinal
How does removal of CO2 also remove H+?
For every molecule of CO2 eliminated, an H+ is bound to H2O removing it from solution
2nd most important buffer in the body
proteins (ex: Hb, myoglobin)
Increasing V’A –> PaCO2?
decrease
Respiratory acidemia
low pH due to change of breathing. A retention of CO2 generally caused by respiratory problems such as hypoventilation
Respiratory alkalemia
high pH due to change of breathing. Excessive loss of CO2 generally caused by hyperventilation
Metabolic acidemia
low pH due to change in body metabolism
Metabolic alkalemia
high pH due to change in body metabolism
How does bicarb. buffer system react to increased acid?
driving force to L. More CO2 will be released by lungs via increased ventilation (i.e. “ketone breathe”)
How does bicarb. buffer system react to increased CO2?
driving force to R. More HCO3- removed by kidneys
low pH, high PaCO2 indicates:
respiratory acidemia
high pH, low PaCO2 indicates:
respiratory alkalemia
low pH, low PaCO2 indicates:
metabolic acidemia
high pH, high PaCO2 indicates:
metabolic alkalemia
High PaCO2 –> HCO3- concentration?
also high.
blood buffer line on Davenport diagram represents:
buffering capacity of blood
4 types of acid-base disturbances
respiratory acidemia
respiratory alkalemia
metabolic acidemia
metabolic alkalemia
How is respiratory acidemia compensated?
metabolically (i.e. kidney retain base HCO3-)
How is respiratory alkalemia compensated?
metabolically (i.e. kidney loses net base HCO3-)
FIRST priority in compensating for an acid-base disturbance
Restore pH
possible causes of metabolic acidemia
diabetes, heart failure, renal failure, diarrhea. Addition/retention of non-volatile acid, or loss of base.
possible causes of metabolic alkalosis
loss of non-volatile acid, intake of base. I.e. - vomiting
Compensation for metabolic acidemia
respiratory compensation. Lungs excrete more CO2 via hyperventilation
Compensation for metabolic alkalosis
respiratory compensation. Lungs excrete less CO2 via hypoventilation
Review Davenport Diagram in notes
:)
Possible causes of respiratory acidosis
insufficient ventilation, CNS depression, obesity, etc.
Possible causes of respiratory alkalosis
CNS mediated hyperventilation, peripheral stimulation of ventilation, hypoxemia, pregnancy, etc.
pH =
-log[H+]. Also, pH = constant + Kidneys/Lungs
