Cardiovascular Histology

  • Both cardiac and vascular tissues are essentially composed of the same three basic layers that occur throughout the entire cardiovascular system. Depending on the particular tissue, certain layers may not exist, may be more or less prominent, or possess specialized features as required for their proper functionality. We first present an overview of the three basic cardiovascular layers and then provide links to particular cardiovascular tissue types.
Basic Layers
  • Tunica Intima:
    • The tunica intima of the cardiovascular system is composed of a layer of endothelium which is invested with a basement membrane lying on top of a thin collagenous meshwork. The endothelium of various vessels can be considerably different and is determined by how much contact tissues require with blood. In most tissues the endothelium is completely continuous; however, it can also be fenestrated as in glomerular capillaries, or discontinuous as in sinusoidal capillaries.
  • Tunica Media:
    • The middle layer of the cardiovascular system is composed largely of myocytes and can vary vastly in thickness depending on the particular tissue. For example, the myocardium of the heart is a giant expansion of the tunica media, while capillaries do not possess this particular layer at all.
  • Tunica Adventitia:
    • Is the outer, largely collagenous, layer of cardiovascular tissues. For large vessels which cannot meet their metabolic demands from the blood which they themselves conduct, small vessels termed vaso vasorum branch through the tunica adventitia and oxygenate the large vessel's outer layers. The coronary arteries are essentially giant examples of Vaso Vasorum required for the enormous metabolic demands of the myocardium.