Final answer:
Skeletal muscles and one-way valves are instrumental in promoting the return of blood to the heart and preventing its backflow in the systemic circulation, respectively.
Step-by-step explanation:
The contraction of skeletal muscles promotes the return of blood to the heart, and one-way valves prevent flow of venous blood away from the heart in the systemic circulation. The venous system is crucial for the regulation of blood pressure and flow, which are controlled by various mechanisms, including vasoconstriction and vasodilation, and the activities of the skeletal muscle pump and respiratory pump. Factors such as venoconstriction enhance venous return by increasing the preload or stretch of the cardiac muscle and therefore increase contraction. Additionally, the valves in the venous system help to maintain a unidirectional flow of blood towards the heart, assisted by the contraction-relaxation cycle of the surrounding skeletal muscles and changes in thoracic pressure due to respiration.