Histology Review Supplement
Cardiovascular Tissue Review
From the PhysioEx main menu, select Histology Atlas. Click on the white Sort By drop-down menu and select Histology Review from the list. Refer to the slides in the Cardiovascular Tissue Slides folder as you complete this worksheet.
Which component of the intercalated disc is a junction that provides the intercellular communication required for the myocardium to perform as a functional syncytium? Gap junctions
The heart is a four-chambered muscular pump. Although its wall can be divided into three distinct histological layers (endocardium, myocardium, and epicardium), the cardiac muscle of the myocardium composes the bulk of the heart wall.
Blood vessels form a system of conduits through which lifesustaining blood is conveyed from the heart to all parts of the body and back to the heart again.
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Generally, the wall of every vessel is described as being composed of three layers, or tunics. The tunica intima, or tunica interna, a simple squamous endothelium and a small amount of subjacent loose connective tissue, is the innermost layer adjacent to the vessel lumen. Smooth muscle and elastin are the predominant constituents of the middle tunica media, and the outermost tunica adventitia, or tunica externa, is a connective tissue layer of variable thickness that provides support and transmits smaller blood and lymphatic vessels and nerves. The thickness of each tunic varies widely with location and function of the vessel. Arteries, subjected to considerable pressure fluctuations, have thicker walls overall, with the tunica media being thicker than the tunica adventitia. Veins, in contrast, are subjected to much lower pressures and have thinner walls overall, with the tunica adventitia often outsizing the tunica media. Because thinwalled veins conduct blood back to the heart against gravity, valves (not present in arteries) also are present at intervals to prevent backflow. In capillaries, where exchange occurs between the blood and tissues, the tunica intima alone composes the vessel wall. The tunica media of the aorta would have a much greater proportion of what type of tissue than a small artery? Elastic fibers In general, which vessel would have a larger lumen, an artery or its corresponding vein?
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Contractile cardiac muscle cells (myocytes, myofibers) have the same striated appearance as skeletal muscle, but are branched rather than cylindrical in shape and have one (occasionally two) nucleus (myonucleus) rather than many. The cytoplasmic striations represent the same organization of myofilaments (sarcomeres) and alignment of sarcomeres as in skeletal muscle, and the mechanism of contraction is the same. The intercalated disc, however, is a feature unique to cardiac muscle. The densely stained structure is a complex of intercellular junctions (desmosomes, gap junctions, fasciae adherens) that structurally and functionally link cardiac muscle cells end to end. A second population of cells in the myocardium composes the noncontractile intrinsic conduction system (nodal system). Although cardiac muscle is autorhythmic, meaning it has the ability to contract involuntarily in the absence of extrinsic innervation provided by the nervous system, it is the intrinsic conduction system that prescribes the rate and orderly sequence of contraction. Extrinsic innervation only modulates the inherent activity.
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Of the various components of the noncontractile intrinsic conduction system, Purkinje fibers are the most readily observed histologically. They are particularly abundant in the ventricular myocardium and are recognized by their very pale-staining cytoplasm and larger diameter. The connective tissue component of cardiac muscle is relatively sparse and lacks the organization present in skeletal muscle. Which component of the intercalated disc is a strong intercellular junction that...