Acid Base Flashcards
What is the difference between acidemia/alkalemia and acidosis/alkalosis?
-emia: simply represents a change in pH, NOT the cause
- osis: describes the process that leads to a change in pH
ie: metabolic or repiratory
Simplified Henderson-Hasselblach (Kaiser-Bleich) equation for relating H+, HCO3-, and PCO2:
[H+] = 24 (PCO2)
—————-
[HCO3-]
~ pH if [H+] = 40
7.4
~pH if [H+] = 50
7.3
~pH if [H+] = 60
7.2
~pH if [H+] = 70
7.1
Two primary mechanisms of managing acid load:
- buffering (HCO3-)
2. Renal excretion
Four ways to increase activity of Na+/H+ antiporter (which gets excess H+ into PROXIMAL tubule lumen):
- incr. Angiotensin II
- incr. SNS drive
- incr. CO2
- DECR. pH
What players are involve in transporting H+ into prox tubule lumen via NH4+?
Glutaminase increases with high H+ (increase activity of carbonic anhydrase)
Makes NH4+ from glutamine
NH4+ gets antiported against Na+
Why is ammoniagenesis (creation of NH4+) favored in cells?
pK is 9 vs cell pK of 7
Two ways urinary H+ is buffered and excreted?
- HPO4- : 1/3
- limited by amount of phosphorus filtered - NH4+ : 2/3
Where are Beta-intercalated cells found?
What do they do?
Collecting duct next to alpha-intercalated cells
They secrete bicarb via Cl- antiporter (good for alkalosis)
Time for kidney to compensate for respiratory acid/base derrangements?
days
Time for lungs to compensate for metabolic acid/base derrangments?
minutes
Primary rise in pCO2 due to lack of ventilation:
respiratory acidosis
Drug/disease causes of respiratory acidosis:
morphine
succinylcholine
GHB
heroin
PE
pulm obstruction
COPD
Increase in fixed acid production:
metabolic acidosis
-not an issue of CO2
Two ways to cause metabolic acidosis:
Increased H+ (lactate, ketones, salycilates, methanol)
Decreased bicarb (diarrhea, laxative abuse)
Pulmonary compensation for metabolic acidosis:
Kussmaul breathing (DEEP, SLOW)
Renal response to acidosis:
Resorb all bicarb
Excrete fixed acid load (NH4, H+ transporters in collecting duct)
Too much breathing decreasing CO2:
Respiratory alkalosis
Renal response to respiratory alkalosis?
BICARB secretion and consumption via:
B-intercalated cells
inhibition of Na+/H+ transporter
Liver converts NH4 to urea which consumes bicarb
Net loss of H+ from extracellular space:
metabolic alkalosis
Causes of metabolic alkalosis?
vomiting
NG tube
Liver/pancreas role in metabolic alkalosis?
Secrete bicarb in anticipation of buffering H+ from stomach that never gets to the duodenum
Where does ammoniagenesis occur?
Proximal tubule
What do you get from ammoniagenesis in the proximal tubule that helps with acid base management?
2 bicarbs for every glutamine molecule
Where is the HCO3/Cl antiporter to get HCO3 back into the blood?
a-intercalated cell
collecting tubule
