Question

A lot of physiological activities change during exercise to provide more oxygen to the skeletal muscles, including changes causing oxyhemoglobin saturation curve to shift. 1) In which direction will the curve shift? 2) What causes the curve to shift? Please provide at least 3 specific causes.

Answer 1

Oxygen–Haemoglobin dissociation curve is a curve that plots the proportion of hemoglobin in its saturated form on the vertical axis against the prevailing oxygen tension on the horizontal axis. This curve is an important tool for understanding how the blood carries and releases oxygen.

Several factors influence the strength with which oxygen binds to hemoglobin. These factors shift or reshape the oxyhemoglobin dissociation curve. A rightward shift indicates that the hemoglobin has a decreased affinity for oxygen. The ability of  hemoglobin to bind to oxygen and hold it decrfeases  but it makes it easier for the hemoglobin to release oxygen bound to it. The effect of this rightward shift of the curve is that more oxygen is released in to tissues thus it increases the partial pressure of oxygen in the tissues when it is most needed, such as during exercise

EXERCISE the oxygen-hemoglobin curve shifts to the RIGHT. This is because of four factors:
1) The decrease in pH (from the muscle cells getting more acidic)

when the body starts physical excercise anaerobic metabolism takes place in the muscle it produces lactic acid which decrease the pH in the muscle. So the curve shift to the right causing the release of more oxygen to muscle tissues.

2) An increase in muscle temperature (from muscle contraction)

increased temperature cause denaturation of the bond between Hb and oxygen and causes increased partial pressure of oxygen , thus more oxygen will be released and the curve shift to the right.

3) An increase in the partial pressure of carbon dioxide (from the working muscles)

Carbon dioxide affects the curve in two ways. First, CO2 accumulation causes carbamino compounds to be generated through chemical interactions, which bind to hemoglobin forming carbaminohemoglobin which cause less affinity of haemoglobin to oxygen causing oxygen release.

Second, it influences intracellular pH due to formation of bicarbonate ion. This is called Bohr effect, that is the decrease in oxygen affinity of haemoglobin in response to decreased blood pH resulting from increased carbon dioxide concentration due to increased metabolism.

4) An increase of a byproduct molecule from glycolysis known as 2,3-BPG.

2,3-Bisphosphoglycerate or 2,3-BPG is an organophosphate formed in erythrocytes during glycolysis. Its production increases during several conditions such as hypoxaemia, chronic lung disease, anaemia, and congestive heart failure where the availabilty of oxygen to peripheral tissue is reduced. 2,3-BPG acts as a heteroallosteric effector of hemoglobin, reducing the hemoglobin's affinity for oxygen by binding preferentially to deoxyhemoglobin. An increased concentration of BPG in red blood cells causes low-affinity state of hemoglobin and so the oxygen-binding curve will shift to the right.