Oxygen transport - methods and oxyhemoglobin

• The blood is the medium used for gas transport throughout the body. • Oxygen is only available in the lungs. Because the partial pressure of oxygen is higher in the alveoli than in the blood, oxygen diffuses into the blood and is transported to systemic cells. • At the tissues the partial pressure of oxygen is higher in the blood than in the cells, so the oxygen moves into the cells where it promotes aerobic metabolism. • Cells generate carbon dioxide during metabolic activity. • The blood transports the carbon dioxide to the lungs for removal. • Oxygen is transported in two ways: • Bound to hemoglobin molecules in red blood cells. • As a dissolved gas in plasma. • Oxygen is not very soluble in water so only a very small percentage is transported as a dissolved gas. • Almost all oxygen is transported bound to hemoglobin molecules located in red blood cells. • Hemoglobin molecules consist of four polypeptide chains. • Each polypeptide chain contains an iron-bearing heme group. • An oxygen molecule binds to each iron ion located in each heme group. • Hemoglobin that is not bound-to oxygen is called deoxyhemoglobin. Loading or association of oxygen to deoxyhemoglobin forms oxyhemoglo-bin.

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