19. Does oxygen bound to hemoglobin affect the partial pressure of oxygen in the blood (yes/no)? Briefly explain your response

Answer 1

It absolutely does affect the partial pressure of oxygen. Since the affinity of an oxygen molecule for heme increases as more oxygen is bound, as the partial pressure of oxygen increases a proportionally greater amount of oxygen molecules are bound. Whereas when you do not have a lot of oxygen bound to hemoglobin the partial pressure of oxygen decreases and this allows the hemoglobin to bind to carbon dioxide much more readily.

Answer 2

The partial pressure of oxygen (Po2) mainly depends on the % saturation of oxygen bound to hemoglobin (So2%), and the oxygen dissolved in the blood (unbound to hemoglobin). (Only a small amount of oxygen is unbound and dissolved in blood by the way). If you take a look at an O2/Hb dissociation curve, you'll see that the graph takes on a sigmoidal shape. This is because when one molecule of oxygen binds to Hb, the affinity for another oxygen to bind to the same Hb molecule increases. This occurs until the hemoglobin protein is fully saturated with a total of 4 bound O2 molecules. To directly answer your question: yes, the more bound oxygen to hemoglobin (the closer we get to 100% saturation of hemoglobin), the higher the partial pressure of O2 is in the blood. With that being said, the closer we get to maximum hemoglobin saturation, the harder it is to increase the partial pressure and so increasing the saturation at that point will barely increase the partial pressure (Po2) of oxygen anymore. However, as stated before, there are still some oxygen molecules that are unbound and dissolved in the blood. This too has an effect on the partial pressure of oxygen in the blood. For example, let's say we've fully saturated all hemoglobin with O2, but you begin to increasingly breathe in more oxygen (say an oxygen mask, or simply just breathing in more O2), that O2 will end up contributing to the total Oxygen content in the blood (total content meaning oxygen bound to Hb as well as oxygen that's dissolved in blood). Again, when Hb is fully saturated with O2 (around 95%+) the partial pressure will barely rise, even if you bring in more O2, for that O2 will dissolve and barley increase the total oxygen content/concentration.

I apologize for not providing a brief answer, but here's what you need to know in short: yes, the more oxygen bound, the more saturated hemoglobin becomes, and the higher the partial pressure of O2 becomes until finally you reach a point of maximum saturation. And the only increase in partial pressure from that point on is the very small amount of of oxygen that dissolves in the blood after all Hb is saturated.

Here's a great article if you'd like to explore this concept more

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4666443/