role of kidneys in acid-base balance Flashcards
what is the normal pH of the ECF
remains between 7.35 and 7.45
- if plasma levels fall below 7.35 (acidaemia), acidosis occurs
- if plasma levels rise above 7.45 (alkalaemia) alkalosis results
- alterations outside these boundaries can affect all body systems: can result in coma, cardiac failure and circulatory collapse
- at pH <6.8 or >8, death occurs
what is the role of an acid
releases h+ into solution
what is the role of a base
remove h+ from solution
what does pH tell you
specifies acidity or basicity of an aqueous solution
what do buffers do?
resist changes in pH
- when h+ is added, buffer removes it
- when h+ removed, buffer replaces it
what are the types of buffer systems
- carbonic acid/bicarbonate
- protein
- phosphate
why is acid base balance important
- all biochemical processes must occur within an optimal pH window
- kidneys are essential for maintaining acid base balance and do this in conjunction with cardiovascular and respiratory system
CO2 + H2O –> H+ + HCO3-
1. the lungs excrete a large amount of co2- this is a potential acid formed by metabolism
2. the kidneys also secrete and excrete non volatile acids produced from normal metabolism which the lungs can’t excrete (eg lactic acid)
3. but, to maintain acid base balance, the kidneys must also reabsorb virtually all filtered HCO3- - this is important as HCO3- acts as a physiological filter
4. this control prevents acidosis or alkalosis
describe the relationship between pH, HCO3- and cO2
- inverse relationship between ph and plasma conc of CO2
- when one goes up the other goes down - so when pCO2 increases, pH decreases (acidosis) as CO2 reacts with water to form carbonic acid
describe the respiratory regulation of acid base balance
- respiratory regulation of pH is achieved via the HCO3-/CO2 (carbonic acid) buffer system
- as pCO2 levels increase, pH decreases
- as pCO2 levels decrease, pH increases - changes in ph levels are detected by peripheral chemoreceptors
- these then act on respiration centres in brain to adjust respiration rates
describe the renal regulation of acid base balance
- the kidneys are the most effective regulator of body fluid pH
- most HCO3- in filtrate is reabsorbed and h+ is also secreted
- if pH of ECF falls: more secretion of h+ into filtrate and reabsorption of HCO3- back into ECF cause pH to increase
- secretion of h+ inhibited when urine pH falls below 4.5
- if pH of ECF increases: secretion of h+ into filtrate and reabsorption of HCO3- declines
- extracellular pH decreases
what happens when acidaemia occurs
we need to increase H+ secretion and HCO3- reabsorption and HCO3- generation in the distal tubule and Collecting duct (intercalating cells)
describe the acid base imbalances
- accumulation of acids and loss of bases leads to increased conc of h+
- so pH drops, leading to acidosis - loss of acids and accumulation of bases leads to decreased conc of H+
- so pH rises and alkalosis occurs
what is acidosis
- ph of body fluids fall below 7.35
- too much H+
how can H+ levels be reduced in acidosis
- excrete it via lungs as CO2 and the kidneys as H+
2. generate more buffer (hco3-) in the kidneys
what is alkalosis
- ph of body fluids climbs above 7.45
- too little h+
