Oxygen Dissociation curve Flashcards
(7 cards)
What does it mean for oxygen dissociation curve to move to RIGHT?
it means that haemoglobin releases oxygen more easily to the tissues.
Hb can “give” more easily
Hb is being more “generous”
What causes the dissociation curve to go right? (Be more generous!)
Think of conditions where tissues are working hard and need more oxygen:
• Increased CO₂ (hypercapnia)
• Increased temperature (fever, exercise)
• Increased 2,3-DPG (seen in chronic hypoxia, high altitude, anemia)
• Decreased pH (acidosis)
Whats DPG123?
when you’re running around or climbing a mountain, your muscles are shouting:
“Hey! We need air!”
That’s when 2,3-DPG shows up.
It taps haemoglobin’s wrist and says:
“Hey buddy, time to let go of that balloon—these kids need it more!”
Example 2
Imagine haemoglobin is like a school bus that picks up oxygen and drops it off where needed
Now…
2,3-DPG is like a little troublemaker who jumps on the bus when it’s empty (no oxygen on board).
It sits right in the middle of the bus and makes the seats uncomfortable.
So when the bus (haemoglobin) tries to pick up more oxygen—
2,3-DPG says:
“Nope! Drop the oxygen off! Don’t hold onto it!”
Because of this, haemoglobin lets go of oxygen faster and easier—which is perfect when your muscles or brain are tired and really need oxygen.
Wheres 23DPG made?
Inside red blood cells
Heres how
Red cells take in glucose and start running it through glycolysis—their only way to make energy, since they have no mitochondria.
Normally, glucose turns into 1,3-bisphosphoglycerate as part of the process. But—
when the body is under stress (like low oxygen or high demand), a portion of that 1,3-bisphosphoglycerate is diverted into a shortcut called the Rapoport-Luebering shunt.
In this shortcut, it gets turned into…
2,3-bisphosphoglycerate (2,3-DPG)!
This happens thanks to a special enzyme:
bisphosphoglycerate mutase (BPGM)
So when body is under stress, redcells make more of 23DPG - allowing cells to release more and more oxygen to the cells!!
23 DPG function
Let’s pretend the red blood cell is like a bakery. It’s always baking 2,3-DPG in small amounts while doing its regular sugar metabolism (glycolysis). But when certain things happen—like:
• Low oxygen (e.g. in anaemia, high altitude, or lung disease)
• High temperature (e.g. during exercise or fever)
• Acidosis (lots of hydrogen ions, like when you’re tired or sick)
…the bakery starts making more 2,3-DPG automatically.
That extra 2,3-DPG piles up inside the red cell and hops onto haemoglobin, saying:
“Alright, time to be generous—oxygen needs to go now!”
What causes the dissociation curve to move to LEFT
• Low CO₂ (hypocapnia)
• Alkalosis (high pH)
• Low temperature
• Low 2,3-DPG
• Fetal haemoglobin (HbF binds O₂ more tightly)
• Carbon monoxide poisoning (binds Hb strongly and blocks O₂ sites)
• Methemoglobinaemia (Hb can’t release O₂ properly)
Why HbF?
Because fetuses need to pull oxygen harder through placental barrier to get oxygen from mummy!
HbF has a higher affinity for oxygen than adult haemoglobin (HbA).
• This left shift allows HbF to steal oxygen from mum’s blood at the placenta—essentially “pulling” it across the placental barrier.
• Once oxygen is inside the fetal bloodstream, it stays bound until it gets to fetal tissues.
fetal tissues are adapted to work in lower oxygen environments. Also, they have:
• Higher cardiac output
• More capillaries per gram of tissue
• And a low tissue pO₂, which eventually pulls oxygen off HbF when it’s needed
So while HbF holds on tightly, the steep oxygen gradient in fetal tissues helps draw it off—like a magnet pulling the last bit of oxygen out.
Why methaem
. Methaemoglobinaemia (MetHb)
• In this condition, iron in haemoglobin is oxidized from Fe²⁺ (ferrous) to Fe³⁺ (ferric).
• Ferric haemoglobin cannot bind oxygen at all—it’s like a broken seat on the oxygen bus.
BUT—it does more damage:
• The remaining normal haemoglobin molecules become “clingy”—they hold onto oxygen more tightly.
• This leads to a left shift, meaning less oxygen is released to tissues.
So tissues become hypoxic, even if blood oxygen levels look okay.
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WHY CO
- Carbon Monoxide (CO) Poisoning
• CO binds to haemoglobin with 200–250× greater affinity than oxygen.
• This blocks oxygen from binding in those spots—so less total oxygen can be carried.
Worse still:
• When CO is bound, it makes haemoglobin “selfish”—it holds onto any remaining oxygen even more tightly.
• This causes a pronounced left shift in the curve.
Result: The blood looks pink and oxygenated, but the tissues are suffocating.
Why Hb gets clingy?
Hb sites work in sync - coperation - togetherness
One oxygen molecule binds → haemoglobin changes shape (from tense T-state to relaxed R-state).
• This makes it easier for the next O₂ molecules to bind.
• The same happens in reverse—once one oxygen leaves, the rest follow more easily.
This is called cooperative binding.
Clinginess = haemoglobin stuck in R-state
• Caused by: carbon monoxide, methaemoglobin, low 2,3-DPG, etc.
• Effect: oxygen stays bound, tissue hypoxia
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