Acid Base Balance Flashcards
What is the Henderson-Hasselbach equation?
describes relationship between pH, bicarbonate (HCO3-), and partial pressure of CO2 (PCO2)
What does the bicarbonate (HCO3-) buffering system do?
maintain pH of extracellular fluid
unique – has the capacity for independent regulation of HCO3- (by kidneys) and PCO2 (by lungs)
What are two other buffering systems involved in maintaining ECF pH?
phosphate (HPO42- )
hemoglobin (Hb-)
How do kidneys contribute to maintaining pH?
by maintaining plasma [HCO3-]
What are some typical sources of acids?
dietary intake
- meat acids > vegetable acids
metabolic byproducts
- volatile acids (ie. H2CO3) – acids that can dissociate easily
- non-volatile acids (ie. H2SO4, H3PO4)
- organic acids (lactic, β-butyric, & acetoacetic acid)
Under normal conditions, how do kidneys accomplish pH maintenance? (2)
reabsorbing any filtered HCO3- (primarily in PT)
pairing generation of NEW HCO3- with secretion of H+ as:
- H2PO4- (titratable acid)
- NH4+
- protons are secreted and ultimately excreted in urinary output
Reabsorption of Filtered HCO3- – Mechanism
see notes
What are the two ways that new HCO3- can be generated?
- through formation of titratable acid
- through excretion of ammonium (NH4+)
Generation of New HCO3-
Formation of Titratable Acid – Mechanism
see notes
Generation of New HCO3-
Excretion of Ammonium – Mechanism
see notes
What does the liver do when the body has a higher acid load?
liver will favour use of glutamine to package nitrogenous waste
- liver will produce more glutamine
- glutamine is then delivered to kidney
What can acid production in body can be influenced by? (3)
- diet: meats produce more acids, vegetables produce fewer acids
- starvation: increased lipid metabolism results in increased production of both β-OH butyric and acetoacetic acid
- trauma, surgery, strenuous exercise, & fever: increased catabolism results in increased acid formation
How much renal acid excretion occurs through titratable acids vs. ammonium under normal conditions?
1/3 to 1/2 as titratable acid (mainly H2PO4-)
- for one titratable acid excreted, we get one new bicarbonate formed
1/2 to 2/3 as ammonium (NH4+)
- for one glutamine, we get two ammonia excreted and two new bicarbonates formed
How does excretion of both titratable acids and ammonium change under acid-loaded conditions?
increased
What is the most effective mechanism for management of increased acid load? Why?
excretion of ammonium
- in response to prolonged acid load, amount of NH3 will be increased further because it’s our most effective way of clearing that acid
- getting rid of more acid through NH3, but also helping replenish bicarbonate buffer system by producing more HCO3-
there’s a ceiling to how much increase we can have in titratable acid
- ie. starvation – for a longer period of time, titratable acid increase plateaus
What are we trying to do when doing acid-base compensation?
fix pH
How do we maintain pH if bicarbonate goes down?
decrease PCO2 to restore 20:1 ratio
How do we maintain pH if bicarbonate goes up?
increase PCO2 to restore 20:1 ratio
What are the variables on a Davenport diagram? (3)
bicarbonate
arterial blood pH
PCO2 – represented by red lines
Compare PCO2 in metabolic acidosis and metabolic alkalosis.
metabolic acidosis and metabolic alkalosis fall relatively similar in terms of where PCO2 is
What are acid-base nomograms used for?
to clinically to assess acid-base disturbances
diagnosis can be made using only blood pH and PCO2
What are metabolic disturbances?
changes in [HCO3-]
How are metabolic disturbances compensated for?
compensation is respiratory – change in PCO2
What is metabolic acidosis? How is it compensated for?
loss of bicarbonate – ie. due to diarrhea
respiratory compensation: decrease PCO2 by hyperventilating (breathe out more CO2)
What is metabolic alkalosis? How is it compensated for?
gain in bicarbonate – ie. due to vomiting
respiratory compensation: increase PCO2 by hypoventilating (breathe out less CO2)
What are respiratory disturbances?
changes in PCO2
How are respiratory disturbances compensated for?
compensation is metabolic – renal change in [HCO3-]
What is respiratory acidosis? How is it compensated for?
higher PCO2 – ie. caused by hypoventilation, obstructive lung disease
metabolic compensation: increase [HCO3-]
What is respiratory alkalosis? How is it compensated for?
lower PCO2 – ie. due to hyperventilation, high altitude
metabolic compensation: decrease [HCO3-]
Compensation of Acid-Base Disturbances
Response to Respiratory Acidosis – Mechanism
see notes
Compensation of Acid-Base Disturbances
Response to Respiratory Alkalosis – Mechanism
see notes
What is acid-base handling conducted by in collecting duct?
intercalated cells
- alpha intercalated cells deal with acid issues
- beta intercalated cells deal with base issues
