Transport of carbon dioxide Flashcards
What are the ways in which carbon dioxide is transported from the tissues to the lungs?
5% dissolved in plasma
10-20% combined with amino groups in the polypeptide chains of haemoglobin to form a compound called carbaminohaemoglobin
75-85% converted into hydrogen carbonate ions (HCO3-) into the cytoplasm of erythrocytes
How are the hydrogen carbonate ions formed?
carbon dioxide reacts slowly with water to form carbonic acid (H2CO3-)
the carbonic acid then dissociated to form hydrogen ions and hydrogen carbonate ions
What speeds up this process?
in erythrocytes there are high levels of the enzyme carbonic anhydrase
this enzyme catalyses the reversible reaction between carbon dioxide and water to form carbonic acid
How is the electrical balance of the cell maintained?
the negatively charged hydrogen carbonate ions move out the erythrocytes into the pasma by diffusion
negatively charged chloride ions move into the erythrocytes
this is known as chlorine shift
Why is it important to convert carbon dioxide?
convertion into hydrogen carbonate ions
the erythrocytes maintain a steep concentration gradient for carbon dioxide to diffuse from respiring tissues into the erythrocytes
What happens to the carbonic acid when the blood reaches the lung tissue?
there is a relatively low concentration of carbon dioxide
carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into carbon dioxide and water
What happens to the hydrogen carbonate ions and chloride ions when the blood reaches the lung tissue?
hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form more carbonic acid
chloride ions diffuse out of the red blood cells back into the plasma down an electrochemical gradient
How does haemoglobin act as a buffer?
prevents changes in the pH by accepting free hydrogen ions in a reversible reaction to form haemoglobinic acid
