What do veins (except pulmonary) do?

Veins, except for the pulmonary veins, play a crucial role in the circulatory system by carrying deoxygenated blood back to the heart. This function is essential for maintaining proper blood flow and ensuring that blood can be re-oxygenated in the lungs. Deoxygenated blood is the result of various metabolic processes in the body, where oxygen is utilized and carbon dioxide is produced as a waste product. The veins collect this deoxygenated blood from different tissues and organs and transport it back to the right atrium of the heart.

This process is vital because it allows the heart to pump this blood to the lungs for gas exchange, where it can receive oxygen and release carbon dioxide, thus completing the cycle of circulation. Other roles mentioned in the options, such as carrying oxygenated blood to the lungs or controlling blood pressure, do not align with the primary function of systemic veins, which is to return used blood to the heart. Therefore, the accurate representation of the veins' role in the circulatory system is that they return deoxygenated blood back to the heart.