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A right shift of the oxygen-hemoglobin dissociation curve favors oxygen release to tissues. What causes this right shift to occur?

Explanation

Oxygen–hemoglobin dissociation curve:

•Left Shift (oxygen uptake)
-increased pH
-decreased 2, 3-DPG
-lower temperature
-increased CO
-pCO2 decreased

•Right Shift (oxygen release)
-decreased pH
-increased 2, 3-DPG
-increased temperature
-decreased CO
-pCO2 increased

• Understanding the oxygen dissociation curve helps when you consider the oxygen demand from the tissues and the binding and releasing of oxygen from the hemoglobin traveling in the blood. 

• Only 2 or 3% of the oxygen going to the tissues dissolves in plasma; most is attached to hemoglobin molecules. The biggest factor affecting the amount of oxygen that binds to hemoglobin is the partial pressure of arterial oxygen (PaO2); the higher the pressure, the more readily the oxygen combines with the hemoglobin in the red blood cells as oxyhemoglobin. 

• Depending on oxygen demands at the tissue level, oxygen will bind to hemoglobin more or less readily than normal. The position of this curve may shift rightwards (lower saturation for given PaO2) or leftwards (higher saturation for a given PaO2).

• Certain circumstances make the blood more likely to dump oxygen into the tissues, and others make it more likely to cling on to oxygen. Factors that move the oxygen dissociation curve to the right are physiological states where tissues need more oxygen. Active muscle needs more oxygen, so heat, exercise, acidosis, and hypercarbia all cause a shift in the curve rightwards – releasing oxygen. 

• Conversely, when activity is minimal – such as in cold weather or during rest, when the tissues are cold, alkalotic, or hypocarbic, then hemoglobin holds onto oxygen. The curve also shifts leftwards in carbon monoxide poisoning. 

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