University of Texas Medical Branch

Cell Biology Graduate Program

Muscular Arteries

1) Blood vessels contain each of the major tissue types: epithelia (called endothelia), connective tissue, muscle, and nerve fibers. Find your skin slide (slide 25) and look for a muscular artery. The following photograph shows a muscular artery from skin, cut in cross section. The Tunica intima is a simple endothelial layer, made of simple squamous cells.  Underneath is an internal elastic membrane, the elastica interna.  Then, there is a smooth muscle layer, the tunica media.  This is followed by a poorly defined outer elastic layer.  Finally, the Adventia is connective tissue (loose) that blends into the surrounding connective tissue.

Use the above photograph to identify each layer again.  Tunica intima; Elastica interna; Tunica media; elastica externa; adventitia.

Elastic Artery

The elastic artery is a specialized type of artery designed for distension and elasticity. The largest of these also have connective tissue underneath the endothelium. In the following views, the different layers of an elastic artery can be seen. Find your elastic artery slide and compare the morphology with the labeled fields. Also, compare the elastic artery with a muscular artery.  A good example of an elastic artery is the aorta.

Arterioles

Go back to your skin slide (slide 25) and look for arterioles. Arterioles can be differentiated from arteries by the numbers of layers of smooth muscle. Usually there are no more than 6 layers. You can count the rows of nuclei to differentiate an artery and arteriole. How many smooth muscle cell layers can you see in the following photograph which shows two arterioles. Large__________  Small______________. Note the variation in size of the two vessels. The smaller of the two vessels is often called a "precapillary arteriole" because of the number of smooth muscle layers.

Capillaries

Find capillaries in your skin slide and/or in the slide of the spinal cord (Slide 6).   Capillaries are tiny vessels lined by a single layer of endothelial cells. Note, in the following photograph, that one capillary accomodates only one blood cell. This helps you see why reducing the size of blood cells is important for their transport. What cellular layers are missing (tunics) in a capillary?

Veins

Find veins in your skin slide. Veins are distinguished by their thinner wall, valves, collapsed state. The tunica media does not look as well organized as that in the artery or arteriole.  In the following photo, identify the endothelial cells and the tunica media.

Heart

View the slide of the heart with your naked eye. First, hold it up to the light and find the thicker ventricle and the thinner atrium. You may also see the connective tissue projecting at right angles from the bottom of the atrium. This is the "atrioventricular valve". Once you have identified these regions, look at the valve and the muscle of each region with low power.

The endocardium is like that of the elastic artery. It contains a layer of simple squamous endothelial cells along with a subendothelial connective tissue layer. The following photograph shows the layer which lines the inside of the heart. Underneath this layer is cardiac muscle. Note that it continues as the valve (seen in some of your slides).

The myocardium is the actual wall of the heart containing the cardiac muscle itself. It is equivalent to the "tunica media" of the blood vessel. Scan the wall of the heart. The following photo shows cardiac muscle fibers in the wall. Note the branching fibers and the centrally located nuclei. Identify the intercalated disks on this photo. What is their function?

The epicardium is the fatty connective tissue outside the heart. It also contains large coronary arteries. Find this region and identify the arteries or veins. You may have to share your neighbor's slides.

Identify the coronary vessels and adipose tissue on the above photograph.

For practice, draw an overview of your section of the heart. Label:

Endocardium
Atrium
Ventricle
AV-Valve
Myocardium
Epicardium

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