The blue arrow is indicates the tunica intima. The black bracket represents the tunica media and the green bracket is the tunica adventitia. This is the wall of an artery at 400x.
Tunica intima
This is the innermost layer and lines
the lumen of the blood vessels. It consists of simple
squamous epithelium and a thin layer of areolar
CT (basement membrane) to "stick it to the Tunica media." The
basement membrane is often seen as a squiggly line right under the simple
squamous epithelium. The simple
squamous epithelium provides a smooth surface for the blood
to "slide past." The tunica intima is continuous with the endocardium,
makes-up the capillaries and is collectively referred to as the endothelium.
Tunica media
This is the middle layer. It
is made of smooth
muscle and elastic fibers. It is responsible for vasodialation
and vasoconstriction of the blood vessels. It is also the target
tissue for Vasopressin (ADH) Hormone and plays into blood pressure.
Tunica adventitia
This is the most superficial of the
layers. It is made of dense irregular CT with lots of collagen fibers
running in all directions for strength in many different directions.
In many of the slide preps, you can see the collagen fibers as squiggly
lines in this layer.
Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
The blue arrow is indicates the tunica intima. The black bracket
represents the tunica media and the green bracket is the tunica adventitia.
This is the wall of an artery at 400x.
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Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Arteries and veins experience differences in the pressure
of blood flow. As a result, these differences are reflected in the
structure of the vessels. Arteries experience a pressure wave as
blood is pumped from the heart. This can be felt as a "pulse."
Because of this pressure the walls of arteries are much thicker than those
of veins. In addition, the tunica media is much thicker in arteries
than in veins. As a result, arteries seem to have a more uniform
shape - they tend to be more circular in shape than veins.
Veins do not experience the pressure waves that the arteries do. Therefore, they do not need to be as structurally robust, and they are not. The vessel walls of veins are thinner than arteries and do not have as much tunica media. The tunica media is smaller in relation to the lumen than in arteries. Veins appear "floppy" and irregular in shape.
In the following photos, note the different tunicas and their proportions to each other and the lumen.
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Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Back to top
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to Course Supplements Back
to VC Homepage
Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Photo by Theresa Carrera; labeled
by Dr. Janowski-Bell
Back to top
Back
to Index Page Back
to Course Supplements Back
to VC Homepage