(1) Intima. The lumen (hollow central cavity) is lined by a layer of smooth
epithelium known as the intima.
(2) Media. A middle layer of smooth muscle tissue is called the media.
(3) Adventitia. The adventitia is the outer layer of fibrous connective tissue
that holds everything together.
b. Types of Blood Vessels. See figure 9-1 for a diagram of the human
circulatory system. We recognize three types of blood vessels:
Figure 9-1. Scheme of blood vessels.