Human Structure Virtual Histology
    Heart and Circulatory System
     
     

    The Heart

    Examine this trichrome stained specimen and this H&E stained specimen of the heart wall. The trichrome stained specimen nicely demonstrates blood vessels and dense CT in the myocardium. Examine the major features of each of the three layers of the heart on both slides and in the images to the right.

     

     

     

    • The endocardium is lined by endothelium with underlying layers of CT, a middle layer of smooth muscle and an elastic CT, and a subendocardial layer that is connected to the myocardium. The subendocardial layer contains modified cardiac muscle cells (e.g.Purkinje fibers) of the heart’s impulse conducting system. The thickness of the CT layers in the endocardium varies.
       

     

     

     

    • The myocardium is the thickest layer of the heart wall and contains cardiac muscle, connective tissue, and small blood vessels. It is also thicker in the ventricles compared to the atria. Take a look at the image to the right and note how the cardiac muscle fibers are cut in multiple planes of section because these fibers are organized spirally around each chamber.

     

     

     

    • The epicardium is lined by mesothelium with an underlying layer of loose CT that is rich in adipose tissue and contains small nerves and blood vessels as well as the large coronary vessels.

       

    The myocardium is next.