Question

Hemoglobin’s affinity for O2 A. increases in exercising muscle tissue. B. decreases as blood pH increases. C. decreases as blood pH decreases. D. is higher in maternal blood than in fetal blood.

Short answer

Option C.

Step-by-step solution

- Eliminate Incorrect Options

First, evaluate all the given options to eliminate the ones that are clearly incorrect based on what is known about hemoglobin's affinity for oxygen.

- Evaluate Option A

Hemoglobin’s affinity for O2 typically decreases in exercising muscle tissue because muscles produce more CO2 and lactic acid, causing a drop in pH. Therefore, remove option A.

- Evaluate Option B

Consider what happens to hemoglobin's affinity as the blood pH increases (less acidic environment). Hemoglobin’s affinity for O2 actually increases as the pH increases, not decreases. So, remove option B.

- Evaluate Option C

When blood pH decreases (more acidic environment), hemoglobin's affinity for O2 decreases, a principle known as the Bohr effect. This matches the condition described in Option C.

- Evaluate Option D

Understand the relationship between maternal and fetal blood. Fetal hemoglobin has a higher affinity for O2 compared to maternal hemoglobin to facilitate oxygen transfer from the mother to the fetus. Therefore, eliminate Option D.

- Confirm Correct Answer

After evaluating all options, Option C is the correct answer because hemoglobin’s affinity for O2 decreases as blood pH decreases.

Key concepts

Bohr effect

Hemoglobin’s affinity for oxygen is influenced by several factors, one of which is the Bohr effect. Named after Christian Bohr, this phenomenon describes how hemoglobin's oxygen-binding affinity is inversely related to both acidity and the concentration of carbon dioxide. When tissues like muscles are active, they produce more carbon dioxide and lactic acid. This increases the acidity (decreases pH) of the blood in the vicinity. As a result, hemoglobin releases oxygen more readily to supply these working tissues. This is crucial because cells need more oxygen to produce energy when they are active.
In simple terms, the Bohr effect helps ensure that oxygen is delivered where it is most needed by the body. For example, during intense exercise, your muscles benefit from the increased oxygen release facilitated by the Bohr effect.

Blood pH and oxygen affinity

The relationship between blood pH and hemoglobin’s affinity for oxygen is straightforward but critical. Hemoglobin's oxygen-binding affinity decreases as the pH decreases, meaning that it becomes more acidic.
When the blood has a higher pH (less acidic), hemoglobin holds on to oxygen more tightly. This is known as the Bohr effect, and it ensures that oxygen is released in areas where it is most critical. Here’s a quick breakdown of what happens:

• Increased pH (alkaline): Hemoglobin’s affinity for oxygen increases.
• Decreased pH (acidic): Hemoglobin’s affinity for oxygen decreases.

This mechanism helps regulate oxygen delivery throughout the body based on the varying demands of different tissues.

Fetal and maternal hemoglobin

Fetal hemoglobin (HbF) and adult hemoglobin (HbA) have different affinities for oxygen, which is essential for fetal development. Fetal hemoglobin has a higher affinity for oxygen compared to maternal hemoglobin. This difference enables efficient transfer of oxygen from the mother’s blood to the fetus.
Here’s how it works:

• Oxygen-rich blood from the mother passes near oxygen-poor blood in the fetus.
• Due to HbF's higher affinity, it binds oxygen more readily than HbA.
• This allows the fetus to receive the oxygen it needs for growth and development.

This biological design ensures that the fetus efficiently extracts oxygen despite the lower oxygen availability in the surrounding maternal blood.
Once the baby is born, the body gradually replaces fetal hemoglobin with adult hemoglobin, adapting to the new environment where it can breathe on its own.