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Arterial Histology

  • Arteries possess the all three basic histological layers of all cardiovascular tissues (See: Cardiovascular Histology). The diameter and histological features of arteries transition throughout the cardiovascular system in accordance with their different functionalities, allowing for their categorization into three distinct histo-functional subtypes described further below.
Basic Components
  • Tunica Intima: The Tunica Intima consists of a continuous endothelium supported by a delicate elastic and collagenous layer of variable thickness
  • Tunica Media: The Tunica Media consists of a layer composed of variable ratios of muscular and elastic components
  • Tunica Adventitia: The Tunica Adventitia is a variably-thick collagenous layer which contains vaso vasorum in larger arteries
Elastic Artery
  • Function
    • Elastic Arteries are the first to receive blood outflow from the heart and are designed to conduct the enormous blood pressures generated by the heart without significant loss to downstream vasculature. They expand while accepting large volumes of blood from the heart during systole, and rapidly squeeze that blood volume downstream without significant loss of energy. To do so, elastic arteries must be stretchy and possess incredible recoil, which is achieved by large bundles of elastin primarily present in their tunica media. Examples of elastic arteries include the aorta, carotid arteries, and subclavian arteries.
  • Architecture
    • Tunica Intima: A traditional endothelium lying on top of a layer of collagenous tissue.
    • Tunica Media: The most distinctive layer of elastic arteries and possesses alternating layers of elastin and collagen with little smooth muscle.
    • Tunica Adventitia: A largely collagenous layer that possesses vaso vasorum which supply the outer half of the vessels.
Muscular Artery
  • Function
    • Muscular Arteries branch off of the elastic arteries and distribute blood downstream. Examples include the cerebral, coronary, femoral, and radial arteries.
  • Architecture
    • Tunica Intima: Traditional endothelium lying on top of a layer of collagenous mesh which possesses a thin, outermost layer of distinctive elastic tissue known as the Internal Elastic Lamina (IEL)
    • Tunica Media: Outside of the IEL lies the tunica media which is composed of a fairly thick layer of vascular smooth muscle cells, which is itself surrounded by a second, thin sheet of elastic tissue known as the External Elastic Lamina
    • Tunica Adventitia: Is a fairly wide collagenous layer in muscular arteries with interspersed bundles of elastin
  • Function
    • Arterioles branch off the Muscular Arteries and are the main regulators of systemic vascular resistance (See: Arteriolar Physiology).
  • Architecture
    • Tunica Intima: The tunica intima of arterioles is a fairly traditional endothelium supported on a very thin collagenous mesh
    • Tunica Media: Possesses several layers of vascular smooth muscle cells which regulate the diameter of the arteriole
    • Tunica Adventitia: A collagenous layer which merges imperceptibly with the collagen of surrounding tissues