Transport Of Oxygen And Carbon Dioxide In The Blood Flashcards
What adaptations do erythrocytes have to make them efficient at transport?
• Biconcave shape (greater SA for diffusion)
• Biconcave shape helps them to pass through narrow capillaries
• No nucleus (more space for oxygen and haemoglobin)
• Contain haemoglobin (protein that carries oxygen)
What is positive co-operativity?
The arrangement of the haemoglobin molecule makes it so that as soon as one oxygen molecule binds to a haem group, the molecule changes shape making it easier for the next oxygen molecules to bind.
What effect does CO2 have on the affinity of haemoglobin for oxygen?
As the partial pressure of CO2 increases, haemoglobin gives up oxygen more easily (Bohr effect).
Describe the chloride shift.
• In the cytoplasm of the red blood cells, there’s high levels of the enzyme ‘carbonic anhydrase’ which catalyses the reversible reaction between CO2 and H2O to form carbonic acid
• The carbonic acid (H2CO3^-) then dissociates to form hydrogen carbonate ions and hydrogen ions (H^+ + HCO3^-)
• The negatively charged hydrogen carbonate ions move out of the erythrocytes into the plasma by diffusion down a concentration gradient
• Negatively charged chloride ions move into the erythrocytes to maintain the electrical balance
Why is CO2 converted into hydrogen carbonate ions?
It maintains a steep concentration gradient for CO2 to diffuse from the respiring tissues into the erythrocytes.
What happens in the blood when it reaches the lungs?
• There is a relatively low concentration of CO2
• Carbonic anhydrase catalyses the reverse reaction, breaking down carbonic acid into CO2 and H2O
• Hydrogen carbonate ions diffuse back into the erythrocytes and react with hydrogen ions to form more carbonic acid
• When this is broken down by carbonic anhydrase, it releases free CO2 which diffuses out of the blood into the lungs
• Chloride ions diffuse out of the red blood cells back into the plasma down an electrochemical gradient
