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Overview of the Respiratory System

Author(s): Center for Educational Outreach, Baylor College of Medicine

Hemoglobin

Hemoglobin picks up oxygen in the lungs and transports it to other parts of the body. Oxygen-rich hemoglobin, known as oxyhemoglobin, has a bright red color. As oxyhemoglobin releases oxygen, it becomes deoxyhemoglobin, which imparts a bluish tinge to tissues. 

Each hemoglobin molecule can bind four oxygen molecules. When oxygen binds to one subunit, it alters the conformation of the hemoglobin so that oxygen is more readily bound to the remaining unoccupied subunits. Once all subunits are bound and a subunit releases its oxygen molecule, the hemoglobin again changes conformation to more readily unload the remaining three oxygen molecules.