Which structure in the circulatory system contains oxygenated blood?

The structure in the circulatory system that contains oxygenated blood is the aorta. The aorta is the main artery that carries oxygen-rich blood from the left ventricle of the heart to the rest of the body. As the heart pumps, the aorta serves as a major conduit for delivering oxygen to the tissues and organs that require it for metabolism and other physiological functions.

Understanding the roles of other components in the circulatory system helps clarify why they do not carry oxygenated blood. The pulmonary artery carries deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation. Veins typically carry deoxygenated blood back to the heart, with the exception of the pulmonary veins, which return oxygenated blood from the lungs to the heart. Capillaries, while they are the sites of gas exchange where oxygen is delivered to tissues and carbon dioxide is collected to be transported back to the heart, themselves contain a mix of blood depending on the stage of circulation and are not a source of oxygenated blood on their own.