Hemoglobin (Hb) in the blood absorbs oxygen to form oxyhemoglobin [Hb(O2)2], which transports oxygen to the cells. The equilibrium can be generally represented by the following

(though it is actually composed of a series of equilibria in which Hb binds from between 1 and 4 O2 molecules per unit depending on the partial pressure of O2.) The cells consume oxygen, producing water and CO2 as a result of cellular respiration. While de-oxyhemoglobin has alower affinity for CO2 than for O2 it transports CO2 from the tissues back to the lungs. In addition, Hb has a much higher affinity for CO than for O2.

Hb + 2O2(gas) <==> Hb(O2)2

Normal blood pH is about 7.4. Under metabolic stress a situation known as acidosis can result in which the pH of the blood drops. This results in a shift of the above equilibrium to the left. Give an explanation for each of the following observations based upon the principles of equilibrium.

(a) Free hemoglobin readily picks up O2 in the lungs

(B) Oxyhemoglobin releases O2 to the tissues

(C.) A person is hyperventilating, his/her dissolved CO2 levels rise in the blood, what effect will this have on O2 transport to the tissues? Why?

To understand the explanations for each observation based on the principles of equilibrium, we need to consider the concept of Le Chatelier's principle. This principle states that when a system at equilibrium is subjected to a stress, the equilibrium will shift in a way that minimizes the effect of the stress.

(a) Observation: Free hemoglobin readily picks up O2 in the lungs.
Explanation: When the blood is in the lungs, the partial pressure of oxygen (O2) is relatively high compared to other tissues. According to Le Chatelier's principle, increasing the partial pressure of O2 will shift the equilibrium towards the oxyhemoglobin form (Hb(O2)2). Therefore, in the lungs, where there is a high partial pressure of O2, free hemoglobin will readily pick up O2 to form oxyhemoglobin.

(b) Observation: Oxyhemoglobin releases O2 to the tissues.
Explanation: In tissues, where the partial pressure of O2 is relatively low due to high oxygen consumption by the cells, the equilibrium will shift in the opposite direction. According to Le Chatelier's principle, a decrease in the partial pressure of O2 will cause the equilibrium to shift towards the de-oxyhemoglobin form (Hb). Thus, oxyhemoglobin will release O2 to the surrounding tissues.

(c) Observation: A person hyperventilating leads to an increase in dissolved CO2 levels in the blood.
Explanation: The increased breathing rate during hyperventilation leads to a decrease in the partial pressure of CO2 (pCO2) in the blood. According to Le Chatelier's principle, a decrease in the partial pressure of CO2 will shift the equilibrium towards Hb(O2)2, resulting in an increased affinity of hemoglobin for O2. Consequently, this will reduce the amount of O2 released to the tissues, as the equilibrium is favoring the formation of oxyhemoglobin rather than releasing O2. Therefore, hyperventilation, which decreases the pCO2, may hinder O2 transport to the tissues.