Acid base balance Flashcards
how is pH measured?
-log10[H+] or log 1/[H+]
neutral pH is?
7
below 7 pH?
acid
above 7 pH?
alkaline
what do acids do with protons?
donates protons
what do alkalis do with protons?
accepts protons
stronger acid - H+?
stronger the acid the greater the % of molecules separate to free H+ and anions
what pH is needed in a cell for normal cell function?
7
slight deviations in pH cause what to change?
protein structure
enzyme activity
nerve excitability
what does blood pH depend on?
depends only on the ratio of [HCO3-] to [H2CO3]
What is H2CO3?
carbonic acid
a weak acid, a portion dissociates into H+ and HCO3-
Can form from either CO2 + H2O or from H+ + HCO3-
what is HCO3-?
bicarbonate ion
H2CO3 part - dissociates into HCO3- and H+
CO2 combines with OH- (forming HCO3-, by carbonic anhydrase)
carbonate (CO32- combines with H+)
alterations in body pH can occur due to?
metabolism in all tissue - continuous production of CO2
breakdown of food - protein, other organic minerals etc (phosphorus and sulphur - phosphorus and sulfuric acid)
metabolic intermediaries - lactic acid in exercise
how does the body deal with changes in pH?
existence of a buffering system
Bicarbonate buffer system (MAJOR SYSTEM)
The phosphate buffer system
Haemoglobin buffer system
Plasma and cell protein buffer system
what do the kidneys regulate in order to regulate blood pH?
regulation of HCO3-
what do the lungs regulate in order to regulate blood pH?
releasing CO2
pathology of the resp system leads to?
leads to acid base imbalance
regulation of pH by the renal system is done by?
done by:
reabsorbing filtered bicarbonate (HCO3-)
Synthesis of new bicarbonate (HCO3-)
Tubular secretion of H+
describe bicarbonate reabsorption in the nephron?
tubular cells normally reabsorb all the filtered HCO3-
Mostly at the proximal tubule (about 80%)
Remainder in the loop of Henle and distal loop (about 20%)
Once HCO3- is reabsorbed - what happens?
it is reabsorbed into the interstitial space
need to be reabsorbed back into the peritubular capillaries
occurs via Na+/HCO3- co transporters (proximal tubule)
Cl- / HCO3- exchanger (collecting tubules)
Describe H+ secretion:
most excreted H+ gains entry to tubular system from being actively secreted
H+ is secreted into the tubular filtrate by the proximal, distal and collecting tubules
H+ secretion increases when pH is low (or CO2 is high) and decreases when pH is high
No mechanism of reabsorption of H+
Describe how H+ can be secreted?
Electrogenic H+ pump
Na-H+ exchanger
H+ - K+ exchanger
what is the electrogenic H+ pump?
ATP-driven H+ pump (CD)
What is the Na-H+ exchanger?
proximal tubule, DT, CD
H+ secreted in exchange for Na+
what is H+ - K+ exchanger?
electroneutral pump exchanging H+ for K+
what is acidosis?
an abnormal process that produces acidaemia - low pH
what is respiratory acidosis?
this is a low pH where primary defect is an increase in the pCO2
what is metabolic acidosis?
this is a low pH where the primary defect is a decrease in plasma HCO3-
what is alkolosis?
it is an abnormal process that produces alkalaemia - high pH
what is respiratory alkolosis?
this is high pH where primary defect is a decrease in pCO2
what is metabolic alkalosis?
this is high pH where primary defect is an increase in plasma HCO3-
what is the compensatory response in respiratory acidosis?
pCO2 has increased and therefore blood pH has fallen SO
Kidneys will attempt to bring about an increase in plasma HCO3
known as: RENAL COMPENSATION
what is the compensatory response in metabolic acidosis?
Plasma HCO3- has decreased and therefore blood pH has fallen SO
Lungs will increase ventilation, rate of breathing leading to a decrease in pCO2
Known as RESPIRATORY COMPENSATION
What is the compensatory response in respiratory alkalosis?
pCO2 has decreased and therefore blood pH has risen SO
Kidneys will decrease in H+ secretion
Only some HCO3- is reabsorbed but rest excreted. Tubular synthesis of HCO3- is decreased
This is RENAL COMPENSATION
What is the compensatory response in metabolic alkalosis?
HCO3- has increased and therefore blood pH has increased SO
Lungs will increase level of pCO2 by reducing rate of breathing and ventilation
This is RESPIRATORY COMPENSATION
