8.4 Transport of oxygen and carbon dioxide in blood Flashcards
What is haemoglobin?
red pigment that carries oxygen: large globular conjugated protein made up of 4 peptide chains, each with an iron-containing haem prosthetic group
What forms when oxygen binds with haemoglobin?
binds quite LOOSELY to haemoglobin, forming oxyhaemoglobin
Hb + 4O2 = Hb(O2)4
= sign means reversible reaction
What are oxygen levels like in erythrocyte cells when blood enters capillaries in lungs?
relatively low
–> makes a steep conc gradient between inside erythrocyte and air in alveoli
–> oxygen moves into cell and binds to haemoglobin
What is special about the arrangement of haemoglobin?
What is this phenomenon called?
as soon as one oxygen molecule binds to haem group, the molecule changes shape, making it easier for the next oxygen molecules to bind
–> Positive Cooperativity
What happens to the conc gradient after one oxygen molecule binds to haemoglobin?
steep diffusion gradient is maintained as free oxygen conc in erythrocyte stays low
–> occurs until all haemoglobin is saturated with oxygen
What are oxygen levels like in erythrocyte cells when blood reaches the body cells?
Concentration of oxygen in cytoplasm of body cells is lower than that of erythrocytes
–> oxygen moves out of erythrocytes and into the body cells, down a conc gradient
What does it mean when haemoglobin has affinity for oxygen?
the amount of partial pressure of oxygen needed to saturate the haemoglobin molecule
What is partial pressure of oxygen?
amount of oxygen in tissue pO2
–> measured in kPa
When partial pressure for oxygen is high, what occurs?
Ventilation= lung tissue have high pO2
–> more oxygen is able to associate with haemoglobin molecules to be transported
When partial pressure for oxygen is low, what occurs?
In respiring tissue, pO2 is low
–> oxygen dissociates from oxyhaemoglobin and diffuses to respiring cells
Oxygen dissociation curve
S-shaped curve
–> Hb saturation with O2 % is not directly proportional to pO2
How does haemoglobin’s ability to associate with oxygen change as it gets more saturated?
First oxygen molecules associates and changes the conformation of haemoglobin
This makes it easier for the 2nd and 3rd oxygen molecules to associate
However, it is difficult to associate the 4th oxygen molecule (curve plateau below 100%)
Effect of different partial pressures of oxygen on affinity of Hb for oxygen?
At low partial pressure of oxygen,
- Hb oxygen saturation is low, so Hb has a low affinity for O2
At high partial pressure of oxygen,
- Hb oxygen saturation is high so Hb has a low affinity for O2
Why would high altitude animals not respire efficiently at low altitudes
low altitude= pO2 higher than high altitude
–> Llama haemoglobin has higher affinity for oxygen than human haemoglobin ( curve is more shifted to the left)
–> At high partial pressure of oxygen, llama haemoglobin would not dissociate oxygen to respiring tissues
What is the affinity of fetal haemoglobin like?
since a fetus is completely dependent on its mother to supply it with oxygen, oxygenated blood from mother runs close to deoxygenated fetal blood
Fetal Hb has a higher affinity for oxygen than adult haemoglobin at each point,
–> removes oxygen from maternal blood as they pass each other
What is the bohr effect?
Where is it important?
As the partial pressure of CO2 rises, haemoglobin gives up oxygen more easily
–> in active tissue with high partial pressure of CO2, haemoglobin can give up oxygen more readily
–> in lungs where the proportion of CO2 in air is low, oxygen binds to haemoglobin molecules easily
How is carbon dioxide transported to the lungs?
About 5% is carried dissolved in plasma
10-20% combined with amino groups in polypeptide chains of haemoglobin
–> carbaminohaemoglobin
75-85% converted into HCO3- hydrogen carbonate ions in cytoplasm of red blood cells
How are the hydrogen carbonate ions formed?
(equaiton)
CO2 reacts slowly with water to form carbonic acid (H2CO3)
–> acid dissociates to form hydrogen ions & hydrogen carbonate ions)
CO2+H2O = H2CO3 = H+ + HCO3-
Why is most of the CO2 transported through the RBC?
blood plasma, reactions occur slowly
In the cytoplasm of RBCs, there are high levels of enzyme CARBONIC ANHYDRASE
Function of carbonic anhydrase
enzyme catalyses the reversible reaction between CO2 & water to form carbonic acid
–> carbonic acid dissociates to form the H+ & HCO3-
What happens to the H+ ions produced?
they bind with haemoglobin in red blood cells
–> forms haemoglobonic acid (causes haemoglobin to release all the oxygen it is carrying
What happens to the hydrogen carbonate ion produced?
Negatively charged HCO3- ions move out of the blood cell into the plasma via diffusion (down conc gradient)
chloride ions move into erythrocytes to maintain electrical balance
–> chloride shift
What happens to some CO2 that escapes being broken down by carbonic anhydrase enzyme?
They bind directly with the haemoglobin, forming
–> carbaminohaemoglobin
When blood reaches the lung tissue, how does carbon dioxide help with gas exchange?
low conc of CO2 in lung tissue = carbonic anhydrase catalyses the reverse reaction by breaking down carbonic acid (H2CO3) into CO2 + H2O
Hydrogen carboante ions diffuse back into the blood cells and react with hydrogen ions to form carbonic acid
What happens asa result of carbonic acid being broken down in the lung tissue?
free CO2 is released, diffusing out of blood into lungs
Chloride ions diffuse out of the red blood cells and back into the plasma
What does haemoglobin act as during gaseous exchange?
a buffer and prevents changes in pH by accepting H+ ions
–> pH would go down making conditions too acidic for catalyst to work
