Exam 1 Review:  Chapter 19:  Vessel Wall Histology

tunica interna = tunica intima - The innermost layer of an artery or a vein, composed of simple squamous endothelium in direct contact with the blood in the lumen and facing the connective tissue basement membrane on the other side. 

internal elastic membrane - A fenestrated elastic membrane, a layer of somewhat porous elastin fibers, which constitutes the outermost component of the tunica intima of arteries; in the largest arteries is is visible as a bright salmon-pink undulating or scalloped line between the endothelium and the smooth muscle of the tunica media.  aka. internal elastic lamina and internal elastic limiting membrane.  [Note:  There is also a similar external elastic membrane at the outer boundary of the tunica media, but it may be more difficult to see without a special stain.]

tunica media - The middle layer of an artery or a vein, usually the thickest layer, composed of smooth muscle arranged in concentric layers and interspersed with elastic connective tissue; contraction of this smooth muscle is under the control of the ANS and certain hormones; its muscle tone and elastic recoil maintain blood pressure in arteries during diastole; this layer is thinner in a vein than in an artery of the same diameter;

tunica adventitia = tunica externa - The relatively thin but tough outer layer of an artery or a vein, composed of longitudinally oriented collagen and elastin fibers; it attaches the vessel to the surrounding tissues.

adventitia - The outermost connective tissue covering of any organ, vessel, or other structure which is not covered by either a serosal membrane or a tough outer fibrous capsule, it is generally a relatively loose irregular connective tissue not tightly adhering to the covered structure.

Diagram of the tunics of an arterial wall (above):  On the left, the drawing illustrates a typical stain and the tunica media smooth muscle are apparent; on the right, the same arterial wall has been stained with a special stain for elastin and you can see the elastin fibers running between the smooth muscle cells of the tunica media as well as through the loose connective tissue of the tunica externa.

A Muscular Artery

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