A Gap-fill exercise
different layers can be identified in all the components of the circulatory system. The innermost layer is called the tunica . In the heart, this layer is also known as the . The tunica layer of the heart contains blood vessels, lymphatics and tissue. The aorta is an example of an artery. The tunica media of this artery is rich in fibres. The tunica adventitia layer of this arter contains small blood vessels called . This is because this large artery needs its own supply. Muscular arteries have lots of smooth muscle in the tunica layer. There are types of capillary. The most common type is called . Discontinuous capillaries are only found in the . Veins are easy to distinguish from arteries because the of the walls is much less compared to the diameter of the .