7.2 Mass Transport: Transport of oxygen by haemoglobin Flashcards
What is the oxygen dissociation curve?
It is a graph showing the relationship between the saturation of haemoglobin with oxygen , and the partial pressure of oxygen.
What does saturation of haemoglobin with oxygen mean?
It is the ratio expressed as a percentage, of the amount of haemoglobin sites assoicated to an oxygen moelcule relative to the total number of haemoglobin binding sites. Hence, at a 100 percent hameoglobin saturation, every binding site of every haemoglobin is bound to an oxgyen. Hence, at 70 percent saturation, 70 percent of the total number of haemoglobin binding sites is filled with oxygen. And at 50 percent saturation, half the number of haemoglobin binding sites is associated with oxygen. This number is increased with increased partial pressure of oxygen.
Hence, what does 95-99 percent saturation of haemoglobin mean?
This means that 95-99 percent of all haemoglobin binding sites have oxygen bound to it.
Explain oxygen dissociation curve. First part i.e at low ppm of O2.
1) The gradient of the curve is shallow at low ppm of O2.
This means on the graph that there is a low percentage of hameoglobin saturation of oxygen i.e a low number of the total hameoglobin binding sites are associated with oxygen. This is because, the shape of the haemoglobin makes it harder for it to associate with the first oxygen molecule.
Explain the oxygen dissociation curve. 2nd part. I.e. at increased ppm of O2
An increase in ppm of oxygen, means more haemoglobin have associated to atleast 1 oxygen molecule. After the binding of the first oxygen molecule, there is a conformation change in the haemoglobin. meaning more oxygen molecules bind more easily to the haemoglobin. There is a conformation change in shape after each binding of oxygen. I.E. The 3rd oxygen molecule is more easily associated than the 2nd, and the 4th oxygen is more easily associated than the 3rd. (positive cooperativity)
Hence, exponetial growth of total haemoglobin sites bound to oxygen relative to ppm of o2
Gradient of the cruve steepens
Explain the oxygen dissociation curve. 3rd part. i.e. at high O2 ppm
Most of the binding sites of haemoglobin are already associated to an oxygen molecule thus the rate of the heamoglobin saturation to oxygen decreases, because while in theroy the 4th oxygen molecule should be easier to bind, but due to the majority of binding sites occupied, it is less likely for an oxygen molecule to collide with last empty site of the haemoglobin. Hence graph shallower at top and flattens off. Rarely ever gets to 100 percent.
What do dissoication curves further to the left means?
Dessociation curves further to left means that the haemoglobin for this organism (typically multiple dissociation curves in one graph are of different organims with different type of haemoglobins), have a greater oxygen affinity. (readily associates with oxygen but unloads less easily)
Hence, at lower ppm of O2, there is a higher saturation of haemoglobin binding sites with oxygen.
What do dissociation curves further to the right mean?
Dessociation curves further to the right means that the haemoglobin for this oxygen have a lower affintiy for oxygen. Readily dissociates with Oxygen, but less easily associates with oxygen.
What is the Bohr effect?
At increased ppm of CO2, there is a decrease in Ph causing the the haemoglobin to change shape which causes a lower affinity of oxygen in the haemoglobin. (That is why oxygen is released in respiring tissues which release CO2).
Dissociation curve at gas-exchange surfaces e.g. lungs
It is shifted to the left.
As, there is low conc of CO2, as it diffuses out of the blood and excreted out. Hence, the affinity of haemoglobin for oxygen is increased, coupled with the high ppm of O2 in the lungs means that oxygen is readily loaded by the haemoglobin. This reduced CO2 conc has shifted the Oxygen dissociation to the left.
Dissociation curve at respiring tissues (e.g. muscles)
The oxygen dissociation curve is shifted to the right. This is because the conc of CO2 is high, and the conc of O2 is low. O2 is readily dissociated from the haemoglobin into the muscle cells. A lower oxygen affinity means that the graph shifted to the right.
How is Oxygen loaded, transported and then unloaded.
It is loaded at the gas-exchange surface- where CO2 is constantly removed. The PH is slightly raised due to low conc of CO2. The high Ph means that the shape of the haemoglobins is changed to one where the haemoglobin has a high oxygen affinity. (loads oxygen readily).
This is important, because when the haemoglobin is transporting oxygen in the blood, the high affinity means the oxygen is not released.
In tissues, CO2 is released by the respiring tissues. This causes a decrease in Ph of the blood within the tissues as Co2 is acidic. This causes a change in shape of the haemoglobin into one where there is a lower affinity for oxygen. Hence, oxygen more readily unloaded into respiring tissues.
Why is this process of loading,unloading and transporting oxygen ensures there is always sufficent oxgyen for respiring tissues?
1) The higher the rate of respiration
2) The greater the amount of co2 produced
3) The lower the Ph
4) The greater the haemoglobin shape change
5) The more readily the oxygen is unloaded
6) the more oxygen is available for respiration
How does oxygen dissociation vary between tissues of different respiratroy rate?
At tissues with a low respiratory rate, usually only 1 oxygen molecule is released, and at tissues with high respiratroy rate 3 O2 molecules are released. This because the frist O2 molecule that binded to the haemoglobin requires a lot of energy to dissociate.
In humans, where does haemoglobin become saturated?
As the haemoglobin passes through the lungs, it becomes saturated with oxgyen. In practice, not all of the haemoglobin molecules are packed with 4 oxygen molecules. The overall saturation of haemolgobin is around 97%.
