ANATOMY

Detailed explanation-1: -Also notice that, as blood moves from venules to veins, the average blood pressure drops, but the blood velocity actually increases. This pressure gradient drives blood back toward the heart. Again, the presence of one-way valves and the skeletal muscle and respiratory pumps contribute to this increased flow.

Detailed explanation-2: -In blood vessels, most of the resistance is due to vessel diameter. As vessel diameter decreases, the resistance increases and blood flow decreases. Very little pressure remains by the time blood leaves the capillaries and enters the venules.

Detailed explanation-3: -Contraction and relaxation of the circular muscles decrease and increase the diameter of the vessel lumen, respectively. Specifically in arteries, vasoconstriction decreases blood flow as the smooth muscle in the walls of the tunica media contracts, making the lumen narrower and increasing blood pressure.

Detailed explanation-4: -In general, blood pressure decreases from arteries to veins, and this is because of the pressure overcoming the resistance of the vessels.

Detailed explanation-5: -Increased vessel diameter means lesser contact of blood with the vessel walls, thus decreasing the resistance and increasing blood flow velocity. On the other hand, a decrease in vessel diameter means increased contact between blood and vessel wall, thus increasing the resistance and decreasing blood flow velocity.