Final answer:
Blood returns to the heart from veins through a pressure gradient, with the aid of one-way valves, skeletal muscle and respiratory pumps, and venoconstriction. The pressure in the atria during diastole facilitates this return, while the atrial reflex adjusts cardiac output to match venous return.
Step-by-step explanation:
The mechanisms favoring the return of blood from veins to the heart involve several factors. As blood pressure falls in veins but the velocity of blood flow increases, a pressure gradient is created that drives blood back toward the heart. This gradient is essential because approximately 64 percent of total blood volume resides in systemic veins.
Key to this process are the presence of one-way valves which prevent backflow, and the action of the skeletal muscle and respiratory pumps. The skeletal muscle pump increases venous return as muscles contract during movement, squeezing the veins and pushing blood toward the heart. The respiratory pump works similarly during breathing, as pressure changes in the chest cavity propel blood towards the heart.
Vasoconstriction, the constriction of blood vessels, also plays a role by maintaining vascular tone, preventing veins from over-distending and enhancing blood flow. These mechanisms, coupled with the low pressure in the atria during diastole and the atrial reflex adjusting cardiac output, ensure efficient return of blood to the heart, critical for maintaining circulation and proper organ function.