The term 'circulatory passage' refers to the AORTA, which is the main artery of the human body. It carries oxygenated blood from the heart to the rest of the body. The AORTA is the largest artery in the body and is responsible for supplying oxygen and nutrients to the organs and tissues. It is also responsible for carrying away carbon dioxide and other waste products. The AORTA is made up of three layers: the intima, media, and adventitia. The intima is the innermost layer and is composed of endothelial cells. The media is the middle layer and is composed of smooth muscle and elastic fibers. The adventitia is the outermost layer and is composed of connective tissue.