dissociation curve

[faisal 2000]

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i am confusing why po2 and p50 increase in cases (such as high temp) which cause right shifted curve
and decrease po2 and p50 in cases (such as low temp) which cause left shifted curve

 

[FindersFee5]

When the curve is right shifted, hemoglobin has less affinity for oxygen. Therefore, it is more likely to release it, so you need more oxygen in the environment to make sure 50% of it is saturated, which increases the p50.

 

[mk04447]

Temp changes the tertiary structure of the alpha and beta chains. At high temp the shape doesn't hold onto oxygen as well, this releases it to the tissues. This makes sense when you think about it, what makes your muscles heat up? Use. When do your tissues need more oxygen? When they are in use.

 

[faisal 2000]

When the curve is right shifted, hemoglobin has less affinity for oxygen. Therefore, it is more likely to release it, so you need more oxygen in the environment to make sure 50% of it is saturated, which increases the p50.

still not get it
when there is left shifted means increase in hemoglobin's affinity for O2, so it should be increase P50 right ?!

 

[FindersFee5]

still not get it
when there is left shifted means increase in hemoglobin's affinity for O2, so it should be increase P50 right ?!

No, P50 is the amount of oxygen needed to fill half the hemoglobins.

Think of it like this: There are two different clean-up units, a day shift and a night shift. The day shift is energized and picks up every piece of trash they find. The night shift is sleepy and only picks up a quarter of the trash they find. For our analogy, the day shift is left-shifted hemoglobin (MORE likely to pick up oxygen/trash) and the night shift is right-shifted hemoglobin (LESS likely to pick up oxygen/trash), and the p50 is how much trash there needs to be before half of the workers have picked up a piece of trash.

Let's say there are 10 people on each of the shifts. How many pieces of trash do there need to be before half the day shift has picked up a piece? Well, if 1/2 * 10 = 5 people need to pick up a piece of trash, and everybody picks up a piece whenever they find one, then that means the p50 is 5 pieces of trash. The night shift, they need to see 4 pieces of trash before they even pick up 1 piece. 5 people still need to have pieces of trash, so 5*4 = 20. The p50 for the night shift is therefore 20, which is HIGHER than 5. So it makes sense that P50 for hemoglobin with a higher affinity would be lower than p50 for hemoglobin with a lower O2 affinity.

Obviously it's more complicated than this because the oxygen is constantly being unloaded/reloaded, and the p50 is a concentration not an absolute number, but the general principle applies. Does this help?