Acid base regulation :

Acids are substances that can release hydrogen ions (H+) Bases (alkalis) are substances that can accept hydrogen ions
Bases include bicarbonate (HCO3) ions

Balance is governed by the concentration of H ion concentration in body fluids
The number of H+ ions determines the acidity or alkalinity of body fluids . Hydrogen ion concentration and pH are inversely related
I.e., the higher the H+ ion concentration, the lower the pH
pH < 7.35 = acidic
pH > 7.45 = alkaline (base)
Take a note that p letter is small & H is capital

Mechanisms to maintain plasma pH
*Chemical Buffer Systems :
Chemical buffers are present in all body fluids (ICF & ECF), tissue, bone , Help maintain constant pH by continually accepting or releasing free H+ ions -->Act immediately. Effect limited.
mainly Is :- Carbonic acid-bicarb buffer system
- Phosphate buffer system
- Protein buffer system

*Respiratory Regulation :
H+ ions exert direct action on the respiratory center in the brain

Acidemia -->increases respiratory rate and depth
Alkalemia-->decreases respiratory rate and depth
The lungs control the CO2 (and thus carbonic acid H2CO3) content in the ECF
An acute rise in PaCO2 stimulates respirations (breaking down H2CO3 into CO2 and H2O)
When pH is alkaline, respirations will be depressed to retain CO2 & H2O to increase H2CO3 level
Occurs in response to metabolic disturbances
Respiratory response occurs within minutes BUT is only temporary or limited in effectiveness
Changes in respiratory status for any reason can lead to changes in pH

* Renal Regulation :
Most powerful regulator, BUT takes hours to days to become functional in controlling acid-base balance
Adjust reabsorption of bicarb and excretion of acids
Good for the long term!!!
_____________________________

Normal Blood Gas
pH 7.35 - 7.45 (7.4)
PaO2 80 - 100 (90)
PaCO2 35 - 45 (40)
HCO3 22-26 (24)
______________________________

Alterations in Acid Base Balance…..

Respiratory Acidosis
Excess of H2CO3 (carbonic acid) in the ECF
Normally…. As plasma H2CO3 increases, the lungs are stimulated to blow off more CO2 thru increased rate/depth of resps
The kidneys attempt to retain more bicarb and excrete H2 ions
*BEFORE COMPENSATION :
pH < 7.35
PaCO2 > 45 mmHg
HCO3 normal
To bring about balance, the body normally initiates
the chemical buffer system
kidneys conserve bicarb & excrete increased H+ ions
Lungs are of little/no use


Respiratory Alkalosis
Deficit of H2CO3 in the ECF
Always d/t hyperventilation which increases loss of CO2
Because CO2 is a resp stimulant, if CO2 is decreased, respiratory depression or cessation of breathing can occur
Kidneys attempt to alleviate the imbalance by increasing bicarb excretion and retention of more H+
Exhibits as:
pH > 7.45
PaCO2 < 38 mm Hg
HCO3 normal ---> beofre compensation

To bring about balance, the body normally initiates
the chemical buffer system
kidneys excrete HCO3 and retain H+ ions



Metabolic Acidosis
Deficit of bicarb (HCO3) as compared with an excess of metabolic acids (H+ ions)

*(before compensation)
pH < 7.35
HCO3 < 22 mEq/L
PaCO2 normal
As the pH decreases with rising levels of acids, the excess H+ ions stimulate chemoreceptors
The chemoreceptors stimulate the resp rate, causing resp compensation
Hyperventilation occurs to compensate & lower the CO2 levels, moving the ratio of CO2 & H2CO3 more toward normal


Metabolic Alkalosis
Increased loss of acid (most often from the stomach or kidneys)
Normally…
Chemical buffer system comes into play
Breathing becomes slower & more shallow so CO2 can be retained
Kidneys retain H+ ions and excreting HCO3
pH >7.45
HCO3 >26 mEq/L
PaCO2 Normal