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The systemic circulation in the human body divides into the arterial blood supply and the venous drainage. These two circulations are linked together by the capillary beds. The arterial blood supply is responsible for perfusing the body with oxygenated and nutrient-rich blood, while the venous blood drainage is responsible for draining the deoxygenated blood and metabolic waste. The venous system drains the deoxygenated blood back towards the heart. Once the venous blood is in the heart, it will get pumped into the pulmonary circulation for gas exchange. After the gas exchange, the oxygenated blood will return to the body via the arterial system. The veins in the venous system are designed to drain the majority of the blood against gravity. The veins have one-way valves. These valves work to prevent the backflow of the blood, allowing for the venous blood to be pumped back toward the heart. The venous system can further divide into superficial and deep venous systems. For example, the venous drainage of the upper limb splits into a superficial and deep venous drainage system. The superficial veins in the upper limb drain the blood from the skin and superficial fascia. The deep venous system will drain the blood from the deeper fascia, muscles, and bones. Even though the venous system may divide into superficial and deep systems, they share many connections with each other. The external forces support the venous blood vessels from the arteries and the muscles contracting to help propel the blood against gravity.