Elastic artery cross-section, coloured scanning electron micrograph (SEM). This section is through a small elastic artery from the lung. The lumen contains red blood cells (red) and platelets (yellow). In the wall of the blood vessel, a clear internal elastic lamina (pale purple) is visible. This elasticity gives rise to the Windkessel effect, which helps to maintain a relatively constant pressure in the arteries despite the pulsating nature of the blood flow. Magnification: x2000 when printed at 10 centimetres across.