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17.4: Layers of the Heart

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    Layers of the Heart

    As mentioned in the previous section, the heart is located in the pericardial cavity formed by the serous membranes of the pericardium. There are two layers of serous membranes (parietal and visceral) with the outer layer being the parietal pericardium which attaches the heart to the mediastinum and has fibrous tissue so the heart does not over-expand. The inner visceral layer is also called the epicardium and it lines the surface of the heart. Between these two membranes is a space, the pericardial cavity, containing a small amount of fluid to reduce friction as the heart moves. Both layers have mesothelium which produces serous fluid.

    The heart wall is composed of three layers (from outside to inside):

    1. epicardium - the same tissue as the visceral pericardium
    2. myocardium - makes up most of heart wall, composed of cardiac muscle tissue (which is made of uninucleated cardiac muscle cells
    3. endocardium - a thin layer of endothelial tissue that lines the heart chambers

    Diagram of the tissue layers of the heart wall and pericardium

    Above: Tissue layers of the heart wall and the pericardium.