Using the slides in this section, you should practice identifying vessels and classifying them into small, medium/muscular, large/elastic, and venules/arterioles. Vessels are embedded in tissue throughout the body so each slide is taken from different structures in the body. At this time, focus on the vessels in the tissues, you will learn specifics of these structures in other lab lessons. There is a brief description of each slide under each picture. You can click on the image or the slide title to bring you to the digital slide.

The aorta is classified as a large/elastic artery. It is the largest artery of the body and consists of 3 layers: tunica intima, tunica media, and tunica adventitia. The tunica intima is the thinnest layer, lined with endothelial cells along the lumen. Within the tunica media, you will find layers of fenestrated elastic laminae (dark pink wavy bands) among smooth muscle and collagen. The elastic laminae in the media have large fenestrations. In reality, they are concentrically arranged tubes of elastic fibers with large holes (fenestrations) in the wall of the tubes. Thus, in cross section, the laminae appear discontinuous due to the holes. When the left ventricle contracts, the wall of the aorta bulges out, storing some of the energy of systole (ventricular contraction) by dilating the fenestrated elastic laminae. When systole ceases, the fenestrated elastic laminae spring back to their original shape. This elasticity helps propel blood along the aorta away from the heart. The tunica adventitia is fairly thick in the large artery. You will find smaller blood vessels called the vasa vasorum surrounded by loose connective tissue. To see the aorta in a different stain that highlights the elastic fibers, see the “More Practice Vessels” section below.

Use this slide to identify the cross section of an artery, vein and nerve. Then determine the size you would assign to the artery and vein (small, medium, or large?). The most obvious difference between the two vessels is the ratio of thickness of media to vessel diameter. There are many different size vessels in this slide, you should be able to identify medium, small, venules, arterioles, and capillaries. Note also that the outline of the artery is relatively smooth whereas the outline of the vein is irregular. Identify the three tunics/layers of the largest vessels you see in the image.

Mesentery is found in the abdomen attached to the small and large intestines. It carries blood vessels, lymphatic vessels, nerves and lymph nodes. You can easily see several lymph nodes with germinal centers. The surrounding tissue is loose connective tissue filled with adipocytes. Use this slide to practice identifying different size vessels. You can also examine the different cell types and tissue types found withing vessels including endothelial cells, smooth muscle cells, fibroblasts of connective tissue, adipocytes, and nerves in larger vessels.

This is an excellent slide for studying smaller vessels like small arteries/veins, arterioles, venules, and capillaries, located in the connective tissue surrounding the elastic cartilage in the middle of the epiglottis. The elastic stain stains the elastic fibers in this specimen a dark purple/black color. A counter stain conveniently stains RBCs yellow so look for these inside blood vessels.  You can find numerous smaller muscular arteries (with a prominent wrinkled internal elastic lamina, 5-10 layers of smooth muscle in the media, and a sparse external elastic lamina. Arterioles have about 2 layers of smooth muscle in the media and little or no internal elastic lamina. The distinction between the smallest muscular arteries and the largest arterioles is slight and of no great significance. The arteries may be accompanied by veins and the arterioles may be accompanied by venules. Capillaries are also present.

Efferent ductules (lumen with pseudostratified columnar epithelium) in the male reproductive system are surrounded by a large amount of CT (pink stroma). Use this section to identify small arteries and veins, arterioles and venules, and capillaries. Review the differences between small vessels, arterioles/venules, and capillaries.

This is a thin plastic section of the liver. It consists of cords and plates of hepatic parenchymal cells surrounded by hepatic sinusoids. In any given organ, the parenchymal cells are the organ-specific cells. Be aware that many organs have both parenchymal and nonparenchymal cells, e.g., CT, blood vessels, nerves, lymphatics. A sinusoid is a generic term for a capillary. It implies that there is sluggish, meandering blood flow through a network of capillaries with large lumina. Sinusoids are also found in bone marrow, the spleen, endocrine organs, etc. Sinusoids are just capillaries. The hepatic sinusoids carry nutrient-laden blood from the GI tract and as they pass by the hepatic parenchymal cells, the nutrients leave the blood and enter the liver, for processing. Hepatic sinusoids are unusual capillaries. They are intermingled stretches of discontinuous capillaries and fenestrated continuous capillaries, although these details are not visible in this slide. Furthermore, there are two distinct types of marginal cells. One is a flattened, typical endothelial cells and the other is a fatter, phagocytic Kupffer cell. The capillaries here have one additional peculiarity—they have a thin, discontinuous basement membrane.  In this preparation, one can see numerous flattened endothelial cell nuclei but the Kupffer cell nuclei are harder to locate and difficult to differentiate from hepatic parenchymal cells.

Using the slides in this section, you should be able to identify the different layers of the heart and describe function of different cell types.

This specimen contains the thin endocardium at the bottom of the slide. The majority of the specimen consists of the myocardium. You should be able to identify the typical structure of myocytes and Purkinje fibers. There are also some vessels throughout the specimen.

How would you describe the difference between a Purkinje fiber and a typical myocyte? Think about what the stored glycogen would do to the cytoplasm.

This specimen of the heart has some excellent examples of Purkinje fibers, located on the endocardial surface of the heart in a small, oval, lightly stained areas. The pericardial surface, with some adipose tissue and a large blood vessel is in the top of the slide. Compare and contrast standard cardiac myocytes with Purkinje fibers using this slide. Notice that the  Purkinje fibers are more lightly stained, have a larger diameter, have a few peripheral myofibrils, a centrally placed nucleus, and a large perinuclear clear area that is packed full of glycogen granules when compared with nearby cardiac myocytes.

This is section through the top of the left ventricle (LV). It also includes a part of the wall of the aorta (A) and one of the three cusps of the aortic valve (AV). There is fibrous CT in the valve that merges into the CT (part of the cardiac skeleton) between the ventricle and the aorta. Note that the valve is avascular and covered by an endothelium. The dark ridges found throughout the aorta is artifact from wrinkles in the tissue.

Study the vasculature in this bundle of vessels and nerves.

This specialized stain highlights the elastic fibers in a black/dark purple color. Nuclei appear in a brown color and collagen fibers appear bluish-green.

Slide Iowa Neurovascular Bundle

1. A) Artery; B) internal elastic membrane; C) Medium- prominent internal elastic membrane
2. A) black- tunica intima; B) blue- tunica media; C) green- tunica adventitia
3. A) vein; B) medium- arteries and veins of the same size often travel together.
4. Nerves- as a reminder, peripheral nerves are encapsulated by Schwann cells, areas of lipid are washed out
5. A) black- arteriole (3 layers of SM); B) blue- nerve; C) green- venule (arteries and veins of same size travel together, 1 layer of SM visible)

Slide Michigan 88 Aorta

1. A) green- tunica intima; C) white- tunica media; D) red- tunica adventitia
2. Endothelial cells
3. A) white- elastic fibers; B) green- smooth muscle cells
4. A) red- collagen; B) yellow- nerve; C) blue- arteriole or venule, vasa vasorum

This image contains an atrium and ventricle including an atrioventricular valve leaflet. Identify these gross anatomical structures by zooming in and examining the tissue. You will also see how the valve leaflet is connected by chordae tendineae to a papillary muscle in the ventricle. You can also see the pectinate muscles of the atrium projecting into the lumen.

Slide Michigan 098 AV Heart

1. A) black- ventricle (thicker wall); B) blue- valve; C) green- atrium (thinner wall)
2. yellow- papillary muscle
3. pectinate muscle
4. A) epicardium; B) black- coronary artery; C) blue- coronary vein
5. Area of interest, no questions
6. intercalated discs
7. heart valves are avascular