Venous structures are part of the circulatory system responsible for returning deoxygenated blood from the body back to the heart. They include various types of veins, such as superficial veins located just beneath the skin and deep veins that run alongside muscles. These veins have one-way valves that prevent blood from flowing backward, ensuring efficient circulation. The largest vein in the body is the vena cava, which is divided into the superior and inferior sections. The superior vena cava carries blood from the upper body, while the inferior vena cava transports blood from the lower body. Together, they play a crucial role in maintaining proper blood flow.