Acid-Basics 2: The carbonic acid-Bicarbonate buffer system (AS lecture) Flashcards
what is the equation for the CO2 + H2O
CO2 + H2O <—> H2CO3 <—> H+ + HCO3-
why is the concentration of bicarbonate ions 20 times that of carbonic acid at a pH of 7.4
because carbonic acid (H2CO3) dissociates extremely readily
what is the concentration of bicarbonate ions at pH of 7.4 and how many times bigger is this concentration than that of carbonic acid?
- at pH 7.4, Bicarbonate ion concentration is 24 mmol/L
- this is 20 times largers than that of carbonic acid
what is the pK for the carbonic acid- bicarbonate buffer reaction?
pK = 6.1
what is the drawback of the carbonic acid-bicarbonate buffer system
- can’t protect against pH changes if the pH changes are due to respiratory problems where there is too much or too little CO2
what regulates CO2 in the body
chemoreceptors in the lungs
what regulates HCO3- and H+
kidneys
how long do each of these systems take:
- CO2 regulation via chemoreceptors in the lungs
- HCO3- and H+ regulation via the kidneys
Chemoreceptors in the lungs:
- seconds
Kidneys:
- hours/days
what 2 ways can the kidneys regulate H+, if it is high and HCO3-, if it is low
- If H+ is too high (acidosis), kidneys will cause more H+ to be excreted
- if HCO3- is too low, kidneys will reabsorb more HCO3-
what is the Henderson-Hasselbach Equation
chemical equation that describes the derviation of pH as a measure of acidity in biological chemical systems
define pK
the pH at which 50% ionisation occurs
what is the relationship between:
**- pH and [HCO3-] **
- pH and PaCO2
and what is each controlled by
-
pH ∝ [HCO3-]
- controlled by kidneys -
pH ∝ 1/PaCO2
- controlled by lungs
what can be disturbed if alter PaCO2, HCO3- or H+ levels
pH Homeostasis
why would a patient with diarrhoea have a fall in arterial blood pH
it would fall (i.e acidosis) as pH is proportional to HCO3-
