Following is the schematic representation of exchange of gases in tissues:

First of all the gaseous exchange takes place between the alveoli and blood. Here the alveoli have great partial pressure of oxygen and less partial pressure of CO₂ while in blood the partial pressure of CO₂ is more and partial pressure of O₂ is less. So, exchange of gas takes place between blood and alveoli. The oxygen is transferred to blood and CO₂ is transferred to alveoli.

Same thing happens between blood and cells or other body tissues. Here the partial pressure of oxygen is more in blood and less in tissues while the partial pressure of CO₂ is more in tissues and less in blood. So, exchange of gases takes place and tissues receive oxygen from blood and transfer CO₂ to blood.

In this way tissue receives oxygen.