Final answer:
The decrease in size of the blood vessel lumen due to smooth muscle contraction is known as vasoconstriction (option C). This process is controlled by the autonomic nervous system and affects blood flow and pressure in the body.
Step-by-step explanation:
The decrease in the size of the lumen of a blood vessel by contraction of smooth muscle is called vasoconstriction. Vasoconstriction and vasodilation are mechanisms that regulate blood flow and blood pressure within the body. During vasoconstriction, the smooth muscles in the walls of the blood vessels contract, leading to a narrower vessel diameter, increased resistance, and increased pressure within the vessel but reduced blood flow. In contrast, venoconstriction, which occurs in the veins, also causes the lumen to become more rounded, decreasing resistance, and thus increasing blood flow to the heart by increasing the return of blood and the preload or stretch of the cardiac muscle. The autonomic nervous system controls these processes in response to pressure-sensitive sensory receptors.