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. Also, it increases the amount of oxygen the blood can absorb from our lungs’ alveoli.
What does the Haldane effect do? 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 the lungs’ alveoli can absorb from the blood plasma.
What Is Haldane Effect?
Haldane effect favors 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, allowing 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. Most of the carbon dioxide becomes the HCO3 ion and moves 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 exercise, 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. 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, we have to do it. We must convert the carbon dioxide, a non-polar molecule, into a polar form, bicarbonate. That’s because we want to dissolve the carbon dioxide in the blood. So most 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. It 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 is exercising tissue, this reduces and increases the affinity of hemoglobin for the H+ ions. If we increase hemoglobin affinity for Hydrogen ions, the hemoglobin will bind these ions. So the concentration of these free Hydrogen ions will decrease because they will bind to the hemoglobin.
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. That means that as hemoglobin is binding hydrogen ions, we will ultimately produce even more of the bicarbonate ions. These bicarbonate ions are the polar form of these carbon dioxide molecules. Ultimately, the Haldane effect increases the bicarbonate ions 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. That increases the number of CO2 molecules in this form to 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. 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 to create the new Y coordinate. Notice what that means: as 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. This Haldane effect increases 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 dissolve and leave the red blood cell in the alveolus. The Hemoglobin also releases Hydrogen ions, which bind to the hemoglobin in this area.
What happens to the hydrogen ions? 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. 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 the alveolus can absorb.
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Sources:
Lumb, AB. Nunn’s Applied Respiratory Physiology (5th ed.). Butterworth Heinemann.
Teboul, Jean-Louis; Scheeren, Thomas. “Understanding the Haldane effect.” Intensive Care Medicine.
Siggaard, O; Garby. “The Bohr Effect and the Haldane Effect.” Scandinavian Journal of Clinical and Laboratory Investigation.
Hanson, CW; Marshall BE; Frasch HF. “Causes of hypercarbia with oxygen therapy in patients with chronic obstructive pulmonary disease.” Critical Care Medicine.
