Anatomy and Functional Roles of the Different Type of Blood Vessels

Introduction

As mentioned in previous concepts, the heart generates different pressures as it contracts and relaxes. Pressure generated by the muscular pumping action of the heart is transferred to both the pulmonary (right side) and systemic (left side) divisions of the circulatory system as blood is ejected from the right and left ventricles during each beat. These blood vessels include the arteries, arterioles, capillaries, venules, and veins.

Arteries, Capillaries, and Veins

We previously discussed the different structures of the heart and learned about the flow of blood to and from the lungs. This was our introduction to a few of the major vessels including the pulmonary artery and

veins. We will now begin comparing and contrasting what it means to be an artery, a vein, and a capillary.

Arteries are vessels that transport blood away from the heart towards the capillaries. These vessels are typically oxygen rich.

Veins are vessels that drain blood from the capillaries and transport it towards to the heart. These vessels are typically oxygen poor.

Capillaries are microscopic vessels that allow for the exchange of substances between the blood and tissues.

The Three Tunics

Each of the major blood vessels consist of 3 layers of tissues known as tunics.

The tunica intima (interna) consists of a layer of simple squamous epithelium bound to a subendothelial layer of areolar connective tissue.

The tunica media consists primarily of smooth muscle with a framework of elastic connective tissue.

The tunica externa (adventitia) consists of areolar connective tissue with elastic and collagen fibers.

The major structural differences between the vessels include:

• The tunica media will be thicker in the arteries than veins as they will need to supply more pressure to the blood.
• Veins and venules are the only blood vessels that contain valves to prevent back flow.
• Capillaries are only composed of a layer of endothelium and a basement membrane.

Structure and Function of the Specific Arteries

With this understanding of the layers of the vessels, we can take a closer look at some of the different types of blood vessels. Of all of the blood vessels of the body, the arteries are the strongest and, in some cases, the most elastic. Arteries can be subdivided into two categories, the elastic arteries and the muscular arteries.

The elastic arteries are the largest arteries (2.5-1.0 cm in diameter) that conduct blood from the heart to the more distant muscular arteries. The tunica media consists of large portion of elastic fibers and less smooth muscle than other classes of arteries. These vessels stretch to accommodate blood being ejected from the left ventricle and the elastic fibers help them ‘rebound’ to their original diameter, smoothing out pulsatile blood flow (more on this later)......... Continue