Biochemistry
The hydrogen ion concentration needs to be within tight limits to allow cellular processes to happen efficiently therefore making acid-base balance important.
- The equation above shows that Carbon dioxide and water bind to produce carbonic acid in the blood which then dissociates to release hydrogen ion and bicarbonate.
- pH depends on the ratio of carbon dioxide to bicarbonate.
- When a patient is retaining carbon dioxide the equation shifts to the right and the blood becomes acidic.
- When a patient is blowing off carbon dioxide quickly then the equation shifts to the left and the blood becomes alkalotic.
The lungs remove carbon dioxide through ventilation. PaCO2 is maintained in normal limits by adjusting ventilation in response to CO2 production changes.
The kidneys excrete metabolic acids. They secrete hydrogen ions into urine and the bicarbonate is filtered and returned to the plasma. They try to maintain acid-base balance as well as maintaining stable electrolyte concentrations.
- Respiration controls the CO2 and renal excretion controls HCO3 and therefore when one system is overwhelmed and pH goes out of normal limits, the other system adjusts to compensate and limit the disturbance.
- Respiratory compensation happens quickly within minutes to hours whereas renal compensation takes longer and happens over days.
