O2 and CO2 transport

Question 1

How are red blood cells(erythrocytes) adapted to make them efficient at transporting oxygen

Answer 1

• They have a biconcave shape which increases the surface area available for diffusion
• and allows for a short diffusion pathway
• they contain haemoglobin which bond to oxygen
• no nucleus allows them to fit more haemoglobin in the red blood cell

Question 2

Describe the structure of haemoglobin

Answer 2

• Haemoglobin is a large globular conjugated protein
• it is made up of 4peptide chains each with an iron containing haem prosthetic group
• binds with oxygen to make oxyhemoglobin

Question 3

What does haemoglobin do to ensure efficient uptake of oxygen

Answer 3

• once an oxygen molecule bonds to a haemoglobin, haemoglobin changes shape to make it easier for the next oxygen molecule to bond
• also because oxygen is bound to haemoglobin the free oxygen concentration stays low keeping a steep diffusion gradient between the erythrocyte and the alveoli

Question 4

What is the Bohr effects and why is it important

Answer 4

• at high partial pressure of CO2 haemoglobin gives up oxygen more easily
• it is important because
• in active tissues with high partial pressure of CO2 haemoglobin gives up oxygen more readily
• in the lungs whee the where proportion of CO2 is low haemoglobin picks up oxygen molecules easily

Question 5

How is fetal haemoglobin different to adult and why

Answer 5

• fetal haemoglobin has a higher affinity for oxygen than adult
• this is so the fetal haemoglobin binds to oxygen more easily maintaining a steep concentration gradient of oxygen between the maternal and the fetal blood

Question 6

How is CO2 transported

Answer 6

• 5% is dissolved in the plasma
• 20% is combined with the amino groups on haemoglobin to form carbaminohaemoglobin
• 75% of CO2 is converted into hydrogen carbonate ions in cytoplasm of RBC
• the CO2 slowly reacts with water to make carbonic acid
• the carbonic acid dissociates to form hydrogen ions and hydrogen carbonate ions
  (Enzyme carbonic anhydrase, I’m RBC)

Question 7

Explain the chloride shift and what happens to CO2 when blood approaches the lungs

Answer 7

• negatively charged hydrogen carbonate ions diffuse out of the RBC to plasma down concentration gradient
• chloride ions diffuse in to maintain electrical balance
• by converting CO2 into hydrogen carbonate ions this maintains a steep concentration gradient of CO2 to diffuse out of cells
• carbonic acid and hydrogen carbonate are converted back into CO2 and water which diffuser into the lungs
• haemoglobin binds to free hydrogen ions to form harmoglobinic acid to prevent PH getting higher