For each of the physiological characteristics A–E, select the most appropriate option from the types of blood vessels listed below

A. Option 3 Arterioles. Arterioles are the main source of peripheral resistance in the circulation since the fall in blood pressure across arteriolar vessels is greater than in any other vascular segment.

B. Option 5 Arterio-venous anastomoses. The AV anastomoses in the extremities such as the fingers and toes open up when body temperature rises and the resulting increase in blood flow raises skin temperature so that there is greater heat loss from the skin.

C. Option 2 Arteries. The arteries, especially those near the heart, are highly elastic. This tissue is stretched during systole and the energy so stored is fed back during diastole to maintain the diastolic pressure. Thus the elastic tissue dampens the large pressure gradients generated by the ventricles into the smaller pressure pulses seen in the arterial system.

D. Option 1 Veins. These valves aid return of blood to the heart. When veins are compressed by surrounding muscles or other organs, the valves do not allow retrograde flow of blood, the blood in the veins is forced forward towards the heart.

E. Option 3 Arterioles. The walls of arterioles are relatively thick relative to their lumen because of the comparatively high smooth muscle component. This muscle is controlled by vasoactive substances and vasomotor nerves to regulate local blood flow.