Acid Base Physiology Flashcards
What are the 3 main components that regulate H+ in the body?
Buffers- bicarbonate, proteins, phosphates, etc
Respiratory compensation- alters CO2 leverls
Renal compensation-alters HCO3- levels
Can buffers correct pH?
No, they can “blunt” changes to pH
Which faster: respiratory compensation or metabolic compensation
Respiratory
What is the normal plasma concentration of H+
40nEq/L
4x10-8 moles
What is the normal blood pH range?
7.35-7.45
What is normal blood pH?
7.4
MUST memorize
What is “volatile” acid?
CO2 that is produced in the lungs.
THIS IS THE ONLY VOLATILE ACID IN OUR BODY IF YOU SEE IT ON AN EXAM IT’S CO2
What are non-volatile or fixed acids?
Acids that arise from normal and abnormal processes:
- degradation of amino acids
- lactic acid
- ketones in DKA
Etc
We produce ______mEq/day of fixed acid
50mEq
Due to gluconeogenic utilization of AA’s in the liver,
Sulfuric acid from methionine etc
What is the Henderson-hasselbalch equation?
pH=pK + log [A-]/[HA]
When [A-]=[HA], then what is the pH
pH=pK
Think about it if [a]/[ha] =1, and you take the log of 1, you get 0
What are strong acids?
Have lower affinities for hydrogen ions which easily dissociate from the conjugate base and have LOW pKs
What are weak acids?
Acids that have higher affinities for H+ and do not dissociate as easily from the conjugate base. Have HIGHER pKs
Where are buffers located?
ECF, ICF, bone
What is our first line defense against pH changes?
Buffers
What is the most important buffer in the ECF?
Bicarbonate
Due to its high concentration
What 2 things contribute to a buffer’s effectiveness?
Its concentration
Its pK
Buffers consist of a pair of:
Acid and conjugate base
HA/A-
At low pHs, which will be higher: [HA] or [A-]
[HA]
At high pHs, which will be higher: [HA] or [A-]
[A-]
At what pHs are buffers most effective
+/- one pH unit from their pK
What is the acid/conjugate base pair for the bicarbonate buffer system?
HCO3-/H2CO3
What is the acid/conjugate base pair for the phosphate buffer system?
HPO42-/H2PO4-
At a pH of 7.4, which will be a better buffer:
Phosphate: pK 6.8
Bicarbonate: pK 6.1
Technically phosphate would be a better buffer since its pK is closer to 7.4, but bicarbonate is more important in the blood
What are the 4 buffers in the blood?
- Bicarbonate (53% of total buffering capacity)
- Hemoglobin (35%)
- Proteins (7%)
- Phosphate (5%)
How does hemoglobin act as a buffer?
Imidaizole groups on histidine and α amino groups are the primary buffer sites on ALL proteins
Why is phosphate unimportant in blood?
It is at a low concentration
What are the 3 intracellular buffers?
Proteins- high conc, pK close to 7.4
Phosphate-same as proteins
Bicarb (less important because concentration is low)
How does bone act like an intracellular buffer?
It takes up H+ in exchange for Na+ and K+
May account for a significant amount of buffering capacity during acute acid load
What is the normal range for pCO2?
35-45
What is the normal range for HCO3-?
22-26
Why do we use CO2 to calculate pH if the the equation uses log[A-]/[HA]
Because CO2 drives the formation of H2CO3
[HCO3] pH= pK + log \_\_\_\_\_\_\_\_\_\_\_\_
.03(CO2)
Can you see how that is [A-]/[HA]
Lungs and kidneys regulate CO2 and HCO3 so that the [HCO3]/[CO2] remains near________
20
Can the kidneys AND the lungs compensate for metabolic disturbances (changes in [HCO3])?
Yes, but NOT if the kidneys caused the metabolic defect in the first place
What organ must compensate for respiratory disturbances?
Kidneys only
Compensation takes days
If you go into metabolic acidosis by eating acid or through the formation of metabolic acids, what will happen?
- Plasma HCO3 decreases when you eat acid(causes the acidosis)
- Respiratory system responds by increasing ventilation to expel CO2
- Kidneys synthesize new HCO3
What can cause respiratory acidosis?
Decreased ventilation (drug overdose, airway obstruction)
How will the kidneys respond to respiratory acidosis?
They will synthesize new HCO3 and excrete H+
What can cause respiratory alkalosis?
Hyperventilation (stress, high altitude, etc)
How will the kidneys respond to respiratory alkalosis?
They will excrete HCO3 causing the urine to become alkaline, while the blood pH will decrease
How do you calculate pH using HCO3 and PCO2?
[HCO3]
pH= pK + log ___________
(0.3)(PCO2)
