We all know how critical oxygen is in our daily lives. It is a very important element that us humans uses for respiration. Oxygen is also very critical  because the circulatory system carries it to the cells within the human body by diffusion.  Diffusion definition is spreading things more widely from high to low concentration.

 Oxygen is normally  transported by two ways-dissolved in plasma-1.5%,and bound to hemoglobin-98.5%. As O2 loads, the affinity of Hemoglobin  for it increases making O2 loading very efficient.

 Hb- Hemoglobin 

There are multiple factors by which loading and unloading of oxygen that occurs in Hb. These are as follows and explanation listen below 

• Temperature-At high temperature, dissociation of Hb and oxygen occurs faster. Low temperature results in inhibition of dissociation of Oxygen from Hb.
• pH-At low pH, oxygen gets dissociated from hemoglobin. High pH results in inhibition of oxygen dissociation from hemoglobin.
• BPG– 2,3 bisphosphoglycerate is a molecule that is produced as a by-product of glycolysis. It promotes the dissociation of oxygen from Hb. BPG binds to deoxyhemoglobin and lowers the affinity of Hb towards Oxygen.
• pCO2– When the percentage of carbon dioxide increase in blood, it promotes a decrease in pH by initiating hydrogen ion formation. At low pH, the affinity of the Hb for oxygen is reduced. 

Reference 

• Anatomy and Physiology Publication date 06/02/2021,J. Gordon Betts,
• “Physiology, Carbon Dioxide Transport.” National Center for Biotechnology Information, 1 Sept. 2020, www.ncbi.nlm.nih.gov/books/NBK532988