acid base balance Flashcards
(42 cards)
what is the pH range for life to operate
6.8-7.8 (apart from exceptional circumstances eg. stomach)
what is the optimal blood pH range
7.35-7.45
Ka equation
[H+][A-]/[HA]
what is pKa
a number that describes the acidity of a particular molecule -> calculated by -log(Ka)
what is a buffered solution
a solution in which the addition of an acid or base does not affect the pH of the solution
what are the main physiological buffers (4)
- bicarbonate (HCO3-) -> this is the main buffer
- phosphate (H2PO4 r=or HPO42-)
- plasma proteins
- haemoglobin
what is a volatile acid
an acid that can be excreted by the lungs i.e. CO2
what is the biocarbonate/CO2 chemical equaiton
CO2 + H2O <–(carbonic anhydrase)–> H2CO3 <–> H+ + HCO3-
the latter step occurs via rapid ionisation
what happens to the deconjugated form of H2CO3
H+ excreted by kidneys; HCO3- reabsorbed by kidneys
what are the 3 lines of defence against pH reduction
- bicarbonate
- replenishment of bicarb by kidneys
- removal of CO2
what is the net endogenous acid production
The nonvolatile acid load -determined by the balance of acid and alkali precursors in the diet
how many days could a person survive without the production of new bicarb
5 days
what is renal net acid excretion
the net amount of acid excreted in the urine per unit time - Its value depends on urine flow rate, urine acid concentration, and the concentration of bicarbonate in the urine
what is acidemia
an arterial pH below the normal range (<7.35)
what is alkalemia
an arterial pH above the normal range(>7.45)
what is acidosis
a process that tends to lower the extracellular fluid pH
what is alkalosis
a process that tends to raise the extracellular fluid pH
where is acid produced from in the body
tissue metabolism and diet
where is bicarbonate filtered/resorbed
filtered at the glomerulus, resorbed at the tubules
(and <0.1% excreted in the urine)
what is required to neutralise net endogenous acid production
reclamation of filtered bicarbonate and generation of new bicarb
where does the majority of the bicarb resorption occur
in the proximal convoluted tubules -> this also means that this is where the most H+ is secreted as for each HCO3- reabsorbed, 2H+ are released
bicarb resorption in the early tubular segments MOA (6)
- Na+/K+ ATPase results in build up of Na+ gradient extraceullularly in the renal peritubular fluid (3Na+ out, 2K+ in)
- this allows Na+ to move into the cell from the tubular lumen down its gradient (via Na+/H+ exchanger i.e. H+ out)
- HCO3- in the lumen bonds with H+ ion forming H2CO3
- this is then split into CO2 + H2O
- CO2 enters the cell where it is turned back into H2CO3 and then broken into HCO3-
- HCO3- excreted alongside Na+ via co transporter into the renal interstitial fluid (H+ then leaves cell via mech in step 2)
tubular lumen = filtrate from the glomerulus, interstitial fluid = blood
what transporter is responsible for moving HCO3- into the renal interstitial fluid in the distal tubular segments
Cl-/HCO3- exchangers (down their concentration gradients)
how is new bicarb generated in the kidneys
by product of ammoniagenesis
