The Haldane effect is the opposite of the Bohr effect. The Bohr impact tells us that the concentration of carbon dioxide and hydrogen ions in the blood affects hemoglobin’s affinity for Oxygen. It increases the amount of oxygen that the exercising tissue can absorb. And it also increases the amount of oxygen that the blood can absorb from our lungs’ alveoli.
What Haldane effect does? It talks about how oxygen concentration inside the red blood cell inside our blood affects hemoglobin’s affinity for carbon dioxide and Hydrogen ions. Also, It increases the mouth of Carbon dioxide that the exercising tissue can release into the blood. It increases the number of Carbon dioxide molecules that the lungs’ alveoli can absorb from the blood plasma.
What is Haldane effect?
Haldane effect is the favoring of carbon dioxide unloading or loading by the change in pressure of oxygen. It means oxygen pressure changes help load or unload carbon dioxide. In the lungs, oxygen pressure is high. So it helps unload the carbon dioxide to be released. In the tissues, oxygen pressure is low that allows loading the carbon dioxide to be picked up. So that is called the Haldane effect.
Tissue makes carbon dioxide that comes out. The carbon dioxide comes in, and it loads. The majority of the carbon dioxide becomes the HCO3 ion and moves in the bicarb form to the lungs. It is the reverse of the Bohr effect.
Reaction: CO2 + H2O <=> H+ + HCO3 –
Haldane effect explanation
Let’s begin by taking a look at the following Haldane effect diagram. Let’s suppose I’m moving my arm back and forth. As I move my arm back and forth, the muscle tissue begins to contract, and ATP molecules aren’t produced by those muscle cells. As cells are exercising, they require a greater number of Oxygen molecules to produce ATP. So inside the red blood cells, the Bohr effect causes hemoglobin to unload and release the oxygen, which travels into those exercising cells. Inside the cells is a process called aerobic cellular respiration.
We produce the energy ATP molecules. Now, these ATP molecules are used for muscle contraction for the actin contraction. But, Carbon dioxide molecules, a byproduct, are produced. These cannot be used in any helpful way. So the Carbon dioxide molecules are expelled from the cell and enter the capillary blood plasma. Because Carbon dioxide is nonpolar, only a tiny portion, about 5%, will remain dissolved in the blood plasma.
The majority of it, the rest of it will enter the cytoplasm of the red blood cell. Now once inside the red blood cell, what we have to do is. We have to convert the carbon dioxide, a non-polar molecule, into a polar form, namely the bicarbonate. That’s because we want to be able to dissolve the carbon dioxide in the blood. So the majority of the carbon dioxide in the red blood cell will follow this reaction pathway.
A special enzyme we call carbonic anhydrase will combine Carbon dioxide and water to form the carbonic acid molecule. Then the Carbonic acid is good. It will dissociate into H+ ions and bicarbonate ions. This is where the Haldane effect takes place.
According to the Haldane effect, if we decrease oxygen concentration in the red blood cells, Oxygen’s mouth decreases. Because it travels into the tissue that exercising tissue, as this reduces, increases the affinity of hemoglobin for the H+ ions.
If we increase hemoglobin affinity for Hydrogen ions, the hemoglobin will begin to bind these ions. So the concentration of these free Hydrogen ions will decrease because they will start to bind to the hemoglobin.
Now, what will happen as we decrease this H+ concentration? Reducing the product concentration will shift the equilibrium toward the right side toward the product side. And what that means is as hemoglobin is binding hydrogen ions, we’re going to produce even more of the bicarbonate Ions ultimately.
And it’s these bicarbonate ions that are the polar form of these carbon dioxide molecules. Ultimately, the Haldane effect increases the number of bicarbonate ions that we can store and dissolve in the blood plasma next to the exercising tissue.
Once again, the Haldane effect is that as we decrease Oxygen’s concentration inside the red blood cell as it leaves, it enters our tissue cell. It increases hemoglobin’s affinity to bind hydrogen ions. It shifts the equilibrium to the right side towards the bicarbonate side. And that increases the number of CO2 molecules in this form that we can store and dissolve in the nearby capillary blood plasma.
We can also represent this effect graphically. Let’s look at the following graph. The Y-Axis is the carbon dioxide content in the blood dissolved in the blood. And the X-Axis is the partial pressure of the carbon dioxide in that region in the blood. The curve describes how much carbon dioxide we can fit. How much we can dissolve inside the blood at some given partial pressure of Carbon Dioxide.
As we decrease Oxygen concentration inside the red blood cell, the Haldane effect causes a leftward shift in this curve. But if we consider the Haldane effect, we decrease the oxygen content in our blood next to the exercising tissue. It shifts the curve to the left, and so the new Y coordinate will create. Notice what that means is as the oxygen decreases, we can store even more carbon dioxide inside our blood.
We can also use the Haldane effect to describe how the lungs’ alveoli can absorb more Carbon dioxide from the blood plasma. So the Haldane effect can also explain how oxygen concentration affects carbon dioxide unloading into the alveoli.
Haldane effect mechanism
What’s happening inside our lungs? The oxygen moves down its concentration gradient from the alveolus and into the red blood cell inside our lungs. Now by this Haldane effect, we increase the concentration of oxygen inside our red blood cells. We decrease hemoglobin’s ability to bind Carbon dioxide and H+ ions.
So as OH binds to hemoglobin, it decreases hemoglobin affinity for h+ in CO2. These two molecules are now released. The Carbon dioxide will begin to dissolve and eventually leave the red blood cell and into the alveolus. The Hemoglobin also releases the Hydrogen ions, which bind onto the hemoglobin in this area.
What happens to the hydrogen ions is? They essentially recombine with the bicarbonate ions that came from the blood plasma. Remember, these bicarbonate ions dissolve into the blood plasma while we have the Chloride ions going into the red blood cell, known as the chloride shift.
These move into the cell chloride ions leave the cell. And this recombines with the H+ to reform the carbonic acid. Then that breaks down into carbon dioxide. The carbon dioxide then leaves the cell and enters the alveolus. So the Haldane effect promotes the amount of carbon dioxide that the alveolus can absorb.
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