Compared with blood in the pulmonary veins, blood in the pulmonary arteries has higher concentrations of:O₂H⁺CO₂

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11ecba2d_0fd7_d407_a3bf_d5bddb452bf7_MD0008_00 Blood is circulated throughout the body by the repetitive contraction of the heart, which enables continuous delivery of oxygen and nutrients to the body's tissues, as well as removal of CO₂ (the major metabolic by-product of cellular respiration) and other waste products. The blood vessels involved in circulation can be divided into two circuits: The systemic circuit distributes oxygenated blood (high O₂, low CO₂, low H⁺) containing nutrients to all body tissues via arteries, which carry blood away from the heart. When oxygenated blood reaches the capillaries within the systemic tissues, it delivers O₂ (becomes deoxygenated) and nutrients to the tissues and picks up CO₂. Veins then return the deoxygenated blood (low O₂, high CO₂, high H⁺) back to the heart so that it can enter the pulmonary circuit. The pulmonary circuit pumps deoxygenated blood through the pulmonary arteries to capillaries in the lungs to facilitate gas exchange. The capillaries are in close contact with lung alveoli (air sacs), and at this site, the blood becomes reoxygenated (O₂ is transferred from alveolar air to the blood, and CO₂ is transferred from the blood to the alveolar air). The pulmonary veins then return the oxygenated blood to the heart so that it can be pumped through the systemic circuit (Number I). Compared with oxygenated blood in the pulmonary veins, deoxygenated blood in the pulmonary arteries has higher concentrations of CO₂ (Number III). Blood that is richer in CO₂ is also generally richer in H⁺ ions due to the following reaction that takes place in red blood cells: 11ecba2d_0fd7_d408_a3bf_95fa2fa4abba_MD0008_00 CO2g+H2Ol↔H2CO3aq↔HCO3-aq+H+aq The higher the CO₂ concentration, the more the forward reaction is favored. Therefore, the CO₂-rich blood in the pulmonary arteries also contains more H⁺ ions (has a slightly lower pH) than the CO₂-poor blood of the pulmonary veins (Number II). Educational objective: Within the pulmonary circuit, the pulmonary arteries carry CO₂-rich, O₂-poor blood from the heart to the lungs, where CO₂ is exchanged for O₂. The pulmonary veins then carry CO₂-poor, O₂-rich blood from the lungs to the heart, which then pumps the oxygenated blood to all body tissues.

Compared with Blood in the Pulmonary Veins, Blood in the Pulmonary