Question

Which of the following are responsible for a rightward shift in the oxygen-hemoglobin dissociation curve?

• A. Lower \(PO_{2}\)
• B. Higher \(H_{+}\)
• C. Higher \(pCO_{2}\)
• D. Both (b) and (c)

Hint:

Remember the Bohr effect: increased H\textsuperscript{+} and CO\textsubscript{2} reduce hemoglobin's oxygen affinity, shifting the curve right and enhancing oxygen delivery to tissues.

Answer 1

The Correct Option is D

A rightward shift in the oxygen-hemoglobin dissociation curve indicates decreased hemoglobin affinity for oxygen, facilitating oxygen release to tissues. This shift is caused by factors such as increased hydrogen ion concentration (higher \(H^{+}\), causing lower pH) and increased partial pressure of carbon dioxide (higher \(pCO_{2}\)), both of which occur during increased metabolic activity. Lower \(PO_{2}\) does not cause this shift but reflects oxygen availability.

Therefore, both (b) higher \(H^{+}\) and (c) higher \(pCO_{2}\) cause a rightward shift. 
 

Answer 2

A rightward shift of the oxygen-hemoglobin dissociation curve means hemoglobin releases oxygen more easily at a given oxygen tension, which is useful in actively metabolizing tissue. Check which of the listed factors actually produce this shift.

1. Lower \( PO_{2} \): A lower partial pressure of oxygen describes a point on the existing curve rather than a factor that moves the curve itself. It reflects how much oxygen is available, but by itself it does not change hemoglobin's affinity for oxygen, so this option alone is incorrect.
2. Higher \( H^{+} \): A higher hydrogen ion concentration, meaning a lower pH, is the Bohr effect. Excess \( H^{+} \) binds to hemoglobin and stabilizes its low-affinity deoxy form, shifting the curve to the right so oxygen is released more readily to acidic, metabolically active tissue. This is a genuine cause of the shift.
3. Higher \( pCO_{2} \): Higher carbon dioxide tension also shifts the curve right, partly because \( CO_{2} \) directly binds hemoglobin to form carbaminohemoglobin, and partly because it generates \( H^{+} \) through carbonic acid formation, adding to the Bohr effect. This is also a genuine cause of the shift.
4. Both (b) and (c): Since higher \( H^{+} \) and higher \( pCO_{2} \) both independently shift the curve to the right, and they in fact reinforce each other in metabolically active tissue, the combination of both factors is the option that fully accounts for the rightward shift, making this option correct.

Because both raised hydrogen ion concentration and raised carbon dioxide tension shift the curve to the right, and neither factor alone is the complete answer, the option covering both together is the correct choice.

Therefore, the correct answer is Both (b) and (c).