Final answer:
Resistance provided by blood vessel walls as blood circulates leads to increased blood pressure and decreased blood flow due to vasoconstriction.
Step-by-step explanation:
As blood flows through the circulation, resistance to flow provided by blood vessel walls causes a decrease in blood flow and an increase in blood pressure. Vasoconstriction, the narrowing of blood vessels, increases resistance and pressure, but decreases the flow of blood. Conversely, vasodilation, the widening of blood vessels, decreases resistance and pressure, thereby increasing blood flow.
Specifically, in arteries, an increase in resistance due to narrowing will result in higher blood pressure upstream of the constriction. However, in veins, the pressure needed to return blood to the heart is lower, and venoconstriction can actually increase blood flow by making the veins more rounded and thereby reducing resistance.