Movement of Carbon Dioxide & Oxygen Flashcards
What happens to CO2 after the respiration of tissue?
The CO2 dissolves into tissue fluid, and then into the blood plasma.
What does CO2 do once dissolved in the blood plasma?
- 5% remains in plasma as dissolved CO2
- 95% diffuses into the cytoplasm
- 10-20% of the CO2 in the cytoplasm binds with amino groups in the Hb, forming carbaminohaemoblin
- The remaining 75-85% forms hydrogen carbonate ions in the erythrocyte’s cytoplasm
How do hydrogen carbonate ions form in the erythrocyte’s cytoplasm?
- CO2 combines with water to form carbonic acid (CO2 + H2O –> H2C03)
- Carbonic acid dissociates, releasing hydrogen ions and hydrogen carbonate ions (H2CO3 –> H+ + HCO3-)
- HCO3- diffuses out of the erythrocyte and into the blood plasma
What enzyme catalyses the formation of carbonic acid?
Carbonic anhydrase
What happens when the hydrogen carbonate ions diffuse out of the erythrocytes?
The chloride shift - chloride ions diffuse into the erythrocytes to maintain charge / electrochemical balance
What happens to the H+ ions released by the dissociation of carbonic acid?
They are taken up by Hb to prevent the erythrocyte from becoming acidic. The Hb acts as a buffer to maintain ph.
This forms haemoglobinic acid.
What are the adaptations of erythrocytes?
- biconcave disc - large SA for exchange
- no nucleus or organelles associated with protein synthesis (ribosomes, rough ER, golgi)
- no mitochondria in mature cells
- contains haemoglobin
- approx 7 micrometers diameter - roughly same as capillaries - shorter exchange pathway
What happens to oxygen when it binds with haemoglobin?
It is taken out of solution, meaning a steep concentration gradient is maintained.
What is haemoglobin?
A large globular, conjugated protein - made up of 4 peptide chains, each containing a haem prosthetic group.
What is positive cooperativity / cooperative binding?
When one oxygen molecule binds to a haem group, the haemoglobin molecule changes shape to make it easier for the next oxygen molecules to bind.
The same happens when removing oxygen molecules.
What is meant by partial pressure?
The concentration of a specific chemical when in a mixture of gases.
What is an oxygen dissociation curve?
A curve showing the percentage saturation of haemoglobin in the blood against the partial pressure for oxygen.
It shows the affinity of haemoglobin for oxygen.
What is meant by affinity for oxygen?
The strength of the interaction between haemoglobin and oxygen.
What is the case on an oxygen dissociation curve at low partial pressure of oxygen?
At low pO2, few haem groups are bound to oxygen, so haemoglobin does not carry much oxygen.
What is the case on an oxygen dissociation curve at higher partial pressures of oxygen?
At higher pO2, more haem groups are bound to oxygen, making it easier for more oxygen to be picked up - the percentage saturation of haemoglobin increases.
Haemoglobin becomes very saturated at high pO2, as all haem groups have bound with oxygen.
What is the Bohr effect?
As the partial pressure of CO2 rises, haemoglobin gives up oxygen more easily - this means the oxygen dissociation curve moves to the right.
Why is the Bohr effect important?
- in active tissues with a high pCO2, haemoglobin gives up oxygen more readily
- in the lungs, where proportion of CO2 in the air is relatively low, oxygen binds to haemoglobin more easily
Why is fetal haemoglobin different to adult haemoglobin?
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin.
- oxygenated maternal blood runs close to deoyxgenated fetal blood.
If fetal haemoglobin’s affinity for oxygen was lower, then little to no oxygen would be transported into the fetal blood.
