Answer
(a) The elasticity of large arteries. Because of the constant pumping action of the heart and the regular variation of blood pressure from systolic to diastolic levels one would expect the blood flow on the arterial side of the circulation to be pulsatile. However, that is not the case because the the large elastic conducting arteries near the heart act as pressure reservoir ad smooth out the transmission of pressure and pulsation. The capillaries are far away from the heart and by the time the blood reaches them the combined effect of elastic artery expansion and recoil and the wall friction along the line has smoothed out any pulsatile action close to imperceptibility
Work Step by Step
The Blood pressure in the heart is highest when the left ventricle contracts ( systolic pressure). This sends a volume o bood( stroke volume) coursing through the aorta and large arteries close to the heart, However, these arteries are elastic arteries with great capacitance , modified for conduction. When the ventricle pumps the extra volume of blood into a relaxed elastic artery, the artery expands and contains the energy and volume of the pumping action instead of transmitting them directly down the line to muscular arteries, arterioles and capillaries. This is well,,since such force would rupture thin-walled capillaries.
When the left ventricle relaxes and the aortic valve closes The elastic artery slowly recoils, evenly transmitting the extra blood to muscular arteries and thence to arterioles and capillaries. The expansion and recoil in response to heart contraction and relaxation evens\ out the blood flow and dampens potential pulses.
