694
UNIT 4
Maintenance of the Body
19
Tunica media
(smooth muscle and
elastic fibers)
Tunica externa
(collagen fibers)
Artery
Vein
Lumen
Lumen
Internal elastic membrane
External elastic membrane
Vasa vasorum
Valve
Artery
Vein
(a)
(b)
Endothelial cells
Basement membrane
Capillary network
Capillary
Tunica intima
Endothelium
Subendothelial layer
Figure 19.1
Generalized structure of arteries, veins, and capillaries.
(a)
Light
photomicrograph of a muscular artery and the corresponding vein in cross section (100
3
).
(b)
Comparison of wall structure of arteries, veins, and capillaries. Note that the tunica media
is thicker than the tunica externa in arteries and that the opposite is true in veins.
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