The Isohydric Principle
- Multiple Buffer Systems of the Body (Fig. 19)
- body fluids contain many buffer pairs, each of which competes for the
same H+ ions
- phosphate and protein buffer systems: closed systems within the body
- bicarbonate buffer system: open system in communication with the external
environment
- only one buffer pair needs to be closely examined to understand the [H+]
in the plasma space
- this is possible because all buffer systems are linked together through
H+ (isohydric principle)
- for biomedical purposes, the bicarbonate buffer system is of primary
importance
- the hemoglobin buffer is of secondary importance
- Accessing the Origin of Acid-Base Disturbances
- malfunctioning respiratory system
- insufficient CO2 removal (respiratory acidosis)
- excessive CO2 removal (respiratory alkalosis)
- malfunctioning metabolic systems
- renal (improper processing of H+ or HCO3-)
- extrarenal (excessive CO2 and H+ production)
- compensations
- the kidneys can compensate for dysfunctional lungs (renal system responds
after a couple of days: slow)
- the lung can compensate for dysfunctional kidneys (respiratory system
responds within minutes: fast)
- lungs and kidneys can both compensate for acid-base disturbances of
extra-renal origin
- the origin of acid-base disturbances and presence of compensations can be
determined
- measurement of bicarbonate buffer pair components and pH (quite simple)
- interpretation of plasma electrolytes concentrations (more complicated)