Question

3) Say an individual has a respiratory disease that causes less CO₂ to be exhaled with each breath.

      a) Would this tend to cause acidosis or alkalosis of the extracellular fluid? Why?

      b) Over the long term, how would the body compensate to bring pH back to normal, even though problems with CO₂ exhalation remain?

Answer 1

3) An individual has a respiratory disease like restrictive lung disorder or Chronic obstructive pulmonary disorder (COPD), then it causes less CO2 to be exhaled with each breadth due to reduced pulmonary ventilation. This reduced pulmonary ventilation of reduced effective alveolar ventiltion the arterial pCO2 is increased above the normal value(40 mm of Hg).

a) This less CO2 exhalation due to respiratory disorder tend to cause respiratory acidosis because,this increase in pCO2 level in the arterial blood enhances the excess H+  production via the following reaction.

H2O+CO2=H2CO3=H++HCO3-

So, as the level of Arterial CO2 level increases the H+ generation also increases. This excess H+ lowers the blood pH below the 7.4 and cause respiratory acidosis of the extracellular fluid.

b) This long term increase in arterial pCO2 causes an increase in pulmonary ventilation. This increase in pulmonary ventilation is caused by maily stimulation of central chemoreceptor. Central chemoreceptor sense the pCO2 level in the blood, and this increase pCO2 level in that person (Suffering from restrictive lung disorder) stimulate the central chemoreceptor by a feed back mechanism. Pneumotaxic centre, Apneustic centre and dorsal,ventral group of neuron in the pons act as central chemoreceptor. These centers sense the increase pCO2 level and causes CO2 washout by pulmonary hyperventilation. This incident also decreases the excess H+ generation in extracellular fluid by increase wash out of CO2 and bring back the pH to normal. There are some peripheral chemoreceptor in the body they also helps in this compensation process via hyperventilation even though problems with CO2 exhalation(restrictive lung disorder or Chronic obstructive pulmonary disorder) remain.