Acid-base Balance Flashcards
What are the three blood buffering systems?
Bicarbonate, phosphate and protein
What is an effective range?
The range a buffer works in
Where is a buffers effective range?
1 pH either side of its pK
Or a factor of 10 either side
What is pK?
The equilibrium constant of a reaction
What relationship does plasma [CO2] have to pCO2 in plasma?
Proportional
How do you convert pCO2 to [CO2]?
0.03
How can you measure blood pH?
Arterial blood gases
What is the normal [HCO3 -]: [CO2]?
20:1
When do buffer solutions resist pH change?
When [base]=[acid]
Why is bicarbonate buffering bad?
pK is 6.1 which isn’t anywhere near the desired plasma pH of 7.4
Why is bicarbonate buffering good?
The body is constantly creating CO2 and we can control both parts of the Henderson hasselbalch equation (through kidneys and lungs)
What are the renal mechanisms for controlling acid- base levels?
Reabsorption and secretion of HCO3 -
Formation of new HCO3 -
Secretion of [H+] into tubular fluids
What buffer systems react with the secreted H+?
HCO3 -: H2CO3
HPO4 2-: H2PO4 -
NH3: NH4 +
What is carbonic anhydrase activity dependant on?
[H+] in the ECF
How much of the filtered bicarbonate is reabsorbed in the proximal tubule?
85-90%
When does H+ react with other buffers in the intercalated cells of the late DCT and collecting duct?
[HCO3 -] is low
Why is the phosphate buffer very effective?
pK = 6.8, which is close to filtrate pH
How does the phosphate buffer work?
HPO4 2- reacts with H+ to form H2PO4 - which is excreted in the urine
How are bicarbonate ions removed from the cell?
Chloride antiporter
What does the tubular epithelium produce from glutamine?
NH3 and alpha ketoglutarate
How much does urinary excretion of ammonium salts increase during metabolic acidosis?
30-50 mMol/day to 300-500 mmol/day
What part of the brain senses blood pH changes?
Medulla oblongata
How does the medulla oblongata sense changes in pH?
CO2 passes the blood brain barrier, where it reacts with water to form H2CO3 which then dissociates into H+ and HCO3 -
What are the two possible ways you can have metabolic acidosis?
Increased ECF [H+] or decreased ECF [HCO3 -]
What can cause metabolic acidosis?
- Severe sepsis or shock (-> lactic acid)
- Uncontrolled diabetes -> overproduction of 3-OH- butyric acid and other keto acids
- diarrhoea -> loss of HCO3 - from GIT
What are the two possible ways you can get metabolic alkalosis?
Characterised by high pH caused by increased ECF [HCO3 -] or decreased ECF [H+]
What can cause metabolic alkalosis?
Excessive thiazide use
Vomiting - loss of H+ from GIT
Ingestion of alkaline antacids
Hypokalaemia
