1. Transport of gases in the blood stream
Transport of blood oxygen and carbon dioxide is essential for internal respiration to occur.
Oxygen carriage in the blood
Oxygen is carried in the blood in the form of:
In chemical combination with hemoglobin as oxyhemoglobin (98.5 % of blood oxygen).
In solution in plasma water (1.5 % of blood oxygen). Oxyhemoglobin is an unstable compound that under certain conditions readily dissociates releasing oxygen.

4. Factors affecting oxygen dissociation:
1- Raised carbon dioxide content of tissue fluid.
2- Raised temperature.
3- Increased 2, 3 – diphosphglycerate (2,3DPG is a substance present in the red blood cells).
In active tissues there is increased production of carbon dioxide and heat which leads to increased release of oxygen. In this way oxygen is available to tissues in greatest need.
When oxygen leaves the erythrocytes, the deoxygenated blood hemoglobin turns purplish in color.

5. Carbon dioxide transport
Carbon dioxide is one of the waste products metabolism. It is excreted by the lungs and is transported by three mechanisms:
1- Most of CO2 is in the form of bicarbonate ions (HCO3 ‾ ) in the plasma.(70% of blood CO2)
2- Some of CO2 is dissolved in the plasma (7% of blood CO2).
3- Some is carried in erythrocytes, loosely combined with a hemoglobin as Carbamino hemoglobin (23% of blood CO2)