Physiological buffering Flashcards
What are acids & bases
Acid = proton donor (increases H+ concentration in solution)
Base = proton acceptor (decreases H+ concentration in solution)
H+ is a proton
What are weak acids
Weak doesn’t relate to concentration
Weak acids don’t fully dissociate in solution
What is pKa
PKa = -log Ka
PKa = pH at which 50% of molecules are ionised
What is Henderson-Hasselbalch equation
What are the clinical implications of modified Henderson equation
Many drugs are weak acids/bases
Un-ionised drugs cross membranes & enter blood stream more easily
Environment has impact on ratio of ionised to unionised drugs
pH at which drugs work depends on how much they dissociate & their pKa
What is the importance of buffering
Buffer is a substance that resists change in pH when small amounts of acids or alkalis are added
Vital to maintain steady pH
If blood pH fluctuates by 0.5 = fatal
Small change in Ph is big change in H+
Describe protein buffers
Increase in pH
Carboxyl group (-COOH) can dissociate & act as weak acid, releasing H+
Carboxyl group becomes carboxylate ion (-COO-)
Decrease in pH
Carboxylate ion (-COO-) & amino group (NH2) can act as weak bases & accept H+
Forms carboxyl group (-COOH) & amino ion (-NH3+)
e.g. histidine & cysteine are important within ECF & ICF
Label the Hb buffer system
What is the phosphate buffer system
Important buffer in ICF & urine
Closed buffer system
Phosphates act as buffer
Important in skeletal muscle cells
What is the bicarbonate buffer system
Important ECF buffer system
Open system
Can excrete waste via lungs or urine
Carbon dioxide dissolved in water is catalysed by carbonic anhydrase (CA)
CA present in many cells (e.g. RBC, renal tubular cells)
Primary role is preventing changes in pH caused by organic & fixed acids in ECF
