Figure 2 shows a photomicrograph of a blood vessel - Edexcel - GCSE Biology Combined Science - Question 2 - 2016 - Paper 1

The structure of a blood vessel is intricately linked to its function in several ways:

1. Thick Walls: The walls of blood vessels, especially arteries, are made up of several layers, including the tunica intima, tunica media, and tunica externa. This thickness is crucial for withstanding high pressure from the blood pumped by the heart.

2. Elasticity: The presence of elastic fibers in the arterial walls allows them to stretch and recoil. This elasticity helps to maintain blood pressure and promotes continuous blood flow during the heart's relaxation phase.

3. Smooth Muscle: The tunica media contains smooth muscle which can constrict or dilate, regulating blood flow and pressure. This ability to change diameter is vital for directing blood supply to different organs based on their needs.

4. Narrow Lumen: The narrow diameter of arteries and arterioles helps to maintain high pressure, facilitating efficient blood transport throughout the body.

5. Endothelial Layer: The innermost layer, composed of endothelial cells, is smooth and reduces friction as blood flows, thus enhancing the efficiency of circulation.