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thumbnail heart h&e 1.25x thumbnail heart h&e 10x
thumbnail heart h&e 20x thumbnail heart h&e 40x

The heart consists of four chambers: at the right atrium the vena cava enters the heart, from the right ventricle the pulmonary artery leaves to the lungs, at the left atrium the pulmonary veins enter, and from the left ventricle the aorta leaves. Between the atria and ventricles are valves (right tricuspid and left bicuspid) composed of connective tissue. The valves and the interior of the chambers are lined by endocardium, a simple squamous epithelium continuous with the endothelium of blood vessels. On the outside of the endocardium is the myocardium, which is composed of cardiac myocytes. These muscle cells have a single centrally located nucleus and are surrounded by collagen. Intercalated disks connect the end of one cardiac myocyte to the beginning of the next. The myocardium also contains Purkinje fibers, specialized muscle cells that are part of the heart’s conducting system, and many capillaries. Myocardium of the left ventricle is much thicker than that of the right ventricle. The outermost layer of the heart wall is the pericardium, connective tissue covered by a single layer of mesothelial cells. The heart is covered by pericardium, a transparent, serous membrane.

The 1.25X micrograph depicts all four chambers of the heart, with the left ventricle having a much thicker muscle wall than the right ventricle, and the aorta. The 10X and 20X micrographs show, in increasing detail, the cardiac myocytes and the blood vessels present in the myocardium. The 40X micrograph displays a Purkinje fiber.

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