20.1a General Structure of Vessels

What are blood vessel walls composed of?

Three layers called tunics.

What is the lumen of a blood vessel?

The space inside the vessel where blood flows.

What are the three tunics of blood vessels?

Tunica intima, tunica media, and tunica externa.

What is the tunica intima?

The innermost layer of a blood vessel wall.

What type of epithelium makes up the endothelium of the tunica intima?

Simple squamous epithelium.

What is the subendothelial layer made of?

Areolar connective tissue.

What is the tunica media?

The middle layer of a blood vessel wall.

What structures are found in the tunica media?

Circularly arranged smooth muscle cells and elastic fibers.

What causes vasoconstriction?

Contraction of smooth muscle.

What happens to the lumen during vasoconstriction?

It narrows.

What causes vasodilation?

Relaxation of smooth muscle.

What happens to the lumen during vasodilation?

It widens.

What is the tunica externa?

The outermost layer of a blood vessel.

What type of tissue is found in the tunica externa?

Areolar connective tissue with elastic and collagen fibers.

What is the function of the tunica externa?

It helps anchor the vessel to surrounding structures.

What fibers are found in the tunica externa?

Elastic and collagen fibers.

What is the vasa vasorum?

Small blood vessels that supply the walls of large vessels.

Why are vasa vasorum needed?

Large vessels are too thick to be supplied directly by blood in the lumen.

Which tunic may contain vasa vasorum?

Tunica externa.

What is the role of small arteries in relation to large vessels?

They supply blood to the walls of very large vessels.