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Blood vessels may be one of the most important tissues examined due to their ubiquitous and extensive presence in every organ. There are three main types of blood vessels: arteries, veins, and capillaries. Arteries and arterioles carry blood away from the heart (Figure 1, Figure 2, and Figure 3). Veins and venules carry blood to the heart. An exception to this generalization are the portal veins, which carry blood from one organ to another (e.g., the hepatic portal vein, which carries blood from the gut to the liver). Capillaries are the smallest vessels and are the site of exchange of oxygen, nutrients, and waste products between the tissues and the blood.
Figure 1 Normal artery within the pancreas in a male F344/N rat from a chronic study. The smooth muscle layer is the thickest layer.
Figure 2 Normal tunica media (asterisks) and tunica intima (arrows) of an artery within the pancreas in a male F344/N rat from a chronic study (higher magnification of Figure 1).
Arteries and veins have walls composed of three layers: the tunica intima, the tunica media, and the tunica adventitia. The tunica intima is composed of endothelial cells on a basement membrane and a subendothelial layer of collagen and elastic fibers. The tunica media consists of smooth muscle cells, elastic fibers, and collagen. The tunica adventitia is composed of collagen and elastic fibers. The relative amounts of each of these components vary depending on the type of vessel. The tunica intima and tunica media of elastic arteries are generally thicker than those of the other types, and the tunica
In NTP studies, changes in blood vessels should be documented in the organ in which they are found and the type of blood vessel identified (e.g., artery or vein). The aorta is considered its own tissue (organ), and lesions in the aorta are recorded as such.
References: Elwell MR, Mahler JF. 1999. Heart, blood vessels, and lymphatic vessels. In: Pathology of the Mouse: Reference and Atlas (Maronpot RR, Boorman GA, Gaul BW, eds). Cache River Press, Vienna, IL, 361-
Mitsumori K. 1990. Blood and lymphatic vessels. In: Pathology of the Fischer Rat: Reference and Atlas (Boorman GA, Eustis SL, Elwell MR, Montgomery CA, MacKenzie WF, eds). Academic Press, San Diego, CA, 473-483.
Authors:
Crystal L. Johnson, DVM, DACVP Veterinary Pathologist II Charles River Laboratories, Inc. Research Triangle Park, NC
Abraham Nyska, DVM, Diplomate ECVP, Fellow IATP Expert in Toxicologic Pathology Visiting Full Professor of Pathology Sackler School of Medicine, Tel Aviv University Timrat, Israel
