In a cross-section of the aorta, its tunica media contains numerous parallel, concentric layers surrounding the aortic lumen. These layers stain specifically for elastic material and are actually elastic lamellae, whose composition is similar to that of elastic fibers. Elastic fibers are also present, particularly in the outer regions of the aortic wall.
The figures show cross-sections of the elastic lamellae at different magnifications.
The elastic lamellae have an important role of these elastic lamellae in the aorta:
– During each systole, the heart contracts and ejects a volume of blood into the aorta.
– The increased volume of blood temporarily stretches and dilates the aortic wall.
– As the blood moves forward through the aorta, the elastic wall recoils toward its previous diameter. This recoil helps maintain the forward movement of blood until the next systole.
This alternating cycle of dilation and recoil helps transform the intermittent pumping action of the heart into a more continuous flow of blood through the arterial system. Blood pressure therefore rises during systole (systolic pressure) and falls during diastole (diastolic pressure), but the elastic recoil of the aortic wall helps reduce the difference between these two pressure levels.
What would happen if the aortic wall could not stretch during systole and recoil during diastole?
The blood would flow as if it were moving inside a tube with rigid walls, such as a plastic or metal tube. The pressure in the aorta would rise sharply during systole and fall sharply during diastole. In the remaining arteries and capillaries of the circulatory system, the blood would be more pulsatile, advance in leaps at each systole, rather than maintaining the continuous flow provided by the elasticity of wall of the aorta.
Aorta. Staining: Weigert. Low, medium, large magnifications.