Acid produced from cellular metabolism is eliminated via the lungs in form of CO2, what is a product of the dissociation and what kind of acid is this?
- Carbonic acid
- Volatile acid
Acid produced from metabolism of protein and eliminated by the kidney is what kind of acid?
- Fixed acid
Calculation of pH
pH = log (1/H+)
What is the first line of defense against pH shift?
Chemical buffer system
1) HCO3- buffer
2) Phosphate buffer
3) Protein buffer
What is the second line of defense against pH shift?
1) Respiratory mechanism (CO2 excretion)
2) Renal mechanism (H+ secretion)
What is the biggest source of acid on a daily base?
Production of CO2 during aerobic respiration
CO2 from aerobic respiration combines with what molecules to form, and then dissociate into?
CO2 + H2O -->H2CO3 --> HCO3- + H+
What is the additional component of the bicarbonate buffer system, molecule involved, and where does it occur?
NaHCO3 in ECF
What does NaHCO3 ionize to?
Almost completely to HCO3- and NA+
What makes up the phosphate buffer system; when does each act?
- NaH2PO4 (acid) which donates H+ when the [H+] falls
- NaHPO4 (base) that can accept a free H+ when the [H+] rises
Where is phosphate significantly concentrated in the kidney?
The tubules, thereby increasing the buffering power of the phosphate system
What are the protein buffers in ICF and ECF?
ECF - albumin
ICF - hemoglobin
Which AA makes these proteins effective buffers, why?
Histidine - can bind or release H+
What is the role of hemoglobin as a buffer in the blood?
- Hb buffers the H+ generated from metabolically produced CO2 in transit between the tissues and the lungs.
- Venous blood is only slightly more acidic than arterial blood despite the large volumes of H+ generating CO2 carried in venous blood
What is the primary ECF buffer against noncarbonic acid charges?
H2CO3:HCO3- buffer system
What is the primary ICF buffer; that also buffers ECF?
Protein buffer system
We only measure the ECF pH clinically while managing patients, but is the ICF pH important; which is more efficient?
- Intracellular pH affects cell function
- Intracellular buffer system is more active and efficient in managing major pH changes
What is the most important buffer against carbonic acid changes and the most important urinary buffer?
Carbonic acid changes = Hemoglobin buffer
Urinary buffer = Phosphate buffer system
What is the calculation for pH when given HCO3- and PCO2?
pH = 6.1 + log ((HCO3-)/(0.03 x PCO2))
If asked to solved for [HCO3-], what is the rearranged equation?
[HCO3-] = 10^(pH-6.1) x 0.03 x PCO2
If asked to solve for PCO2, what is the rearranged equation?
PCO2 = ((HCO3-)/(10^(pH-6.1) x 0.03))
Why does faster, deeper breathing cause pH to rise?
More CO2 eliminated from lungs, which means less H2CO3 is formed, which means less H+ (higher pH)
Which physiologic buffer system responds quickest and which is needed for long term adjustments?
Respiratory = quickest (within minutes) by chemoreceptors sending pH
Renal system = long term adjustments (take 24 hour before kicking in)
How are the kidneys able to regulate pH?
Kindeys can produce HCO3- to replenish lost supplies
- When blood is acidic, kidneys reabsorb HCO3- and excrete H+
- When blood is alkaline, kidneys excrete HCO3- and retain H+
What is acidemia vs. alkalemia and what is the only value needed for measurement?
Acidemia indicated an acid pH (less than 7.35)
Alkalemia indicates an alkaline pH (greater than 7.45)
* Only refer to the pH of blood so this is the only value you need!
Respiratory acidosis; what values?
- Result of abnormal CO2 retention arising from hypoventilation
- pH <7.35 and a PaCO2 above 45 mmHg. HCO3- is normal
Respiratory alkalosis; what values?
- Lungs eliminating too much CO2
- pH > 7.45 and a PaCO2 below 35 mmHg. HCO3- is normal
Metabolic acidosis causes, values?
- Inability of the kidneys to excrete normal amounts of acid or a loss of base
- HCO3- <22 mEq/L and pH below 7.35, PCO2 is normal
Metabolic alkalosis causes, values?
- Loss of stomach acid, excess loss of Na+ or K+, renal loss of H+, or gain of base
- HCO3- >26 mEq/L and a pH >7.45, PaCO2 is normal
Normal range for pH, PaCO2, and HCO3- *KNOW THEM*
What is the mnemoic for determing the cause???
pH = 7.35 -7.45
PaCO2 = 35-45
HCO3- = 22-26
ROME = Respiratory Opposite Metabolic Equal