FIGURE 13.29 • Photomicrograph of the central adrenomedullary vein. This photomicrograph of the human adrenal gland shows a large central adrenomedullary vein with its tributary stained with H&E. The wall of the vein is highly irregular, containing several longitudinally oriented bundles of smooth muscles (SM) that extend into the wall of a tributary. This unique eccentric arrangement of smooth muscles, sometimes called muscle cushions, results in the irregularity in the thickness of the vascular wall. Note that in the cleft between two smooth muscle bundles (asterisk), the lumen of the vein is separated from the chromaffin cells of the adrenal medulla only by the tunica intima. On the opposite side of the wall, muscle bundles are absent (arrowheads) and the cells of the adrenal cortex are in direct contact with the tunica intima. 120. (Courtesy of Dr. Donald J. Lowrie Jr., University of Cincinnati College of Medicine.)  FOLDER 13.3
Clinical Correlation: Ischemic Heart Disease
Ischemic heart disease or ischemic cardiomyopathy is defined as the imbalance between supply and demand of the heart for oxygenated blood. Ischemic heart disease is the most common type of heart disease in the United States and affects approximately 1 in every 100 people. The most common cause of ischemic heart disease is atherosclerosis. The risk of developing atherosclerosis in-creases with age, family history, hypertension, cigarette smoking, hypercholesterolemia, and diabetes. In atheroscle-rosis, the lumina of the coronary arteries progressively narrow because of the accumulation of lipids, extracellular matrix, and cells, leading to the development of atheroma-tous plaques (Fig. F13.3.1). Plaques are formed by intra-cellular and extracellular lipid deposition, smooth muscle proliferation, and increased synthesis of proteoglycans and collagen within the intima of the vessel wall. Blood flow continued next page
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The cardiovascular system is a transport system that carries blood and lymph to and from the tissues of the body. The cardiovascular system includes the heart, blood vessels, and lymphatic vessels. Blood vessels provide the route by which blood circulates to and from all parts of the body. The heart pumps the blood. Lymphatic vessels carry tissue-derived fluid, called lymph, back to the blood vascular system. The heart is a four-chambered organ consisting of a right and left atrium and a right and left ventricle. Blood from the body is returned to the right atrium from which it enters the right ventricle. Blood is pumped from the right ventricle to the lungs for oxygenation and returns to the left atrium. Blood from the left atrium enters the left ventricle from which it is pumped to the rest of the body, i.e., the systemic circulation. The heart, which differentiates from a straight vascular tube in the embryo, has the same basic three-layered structure in its wall as do the blood vessels above the level of capillaries and postcapillary venules. In the blood vessels, the three layers are called the tunica intima, includ-ing the vascular endothelium and its underlying connective tissue; the tunica media, a muscular layer that varies in thickness in arteries and veins; and the tunica adventitia, the outermost layer of relatively dense connective tissue. In the heart, these layers are called the endo-cardium, the myocardium, and the epicardium, respectively.
Atrioventricular septum, heart, human, H&E ×45; inset ×125.