CHAPTER 9
Circulatory System
163
Figure 9-6.
A representation of types of blood vessels: arteries, veins, and capillaries.
Blood vessels
make up the
arterial
, the
venous
, and the
capillary systems
. In general, arteries have smaller, rounder lumens than
veins; their tunica media are thicker than the tunica adventitia, and the IEL are prominent. Veins have larger, fl
atter lumens than
arteries; longitudinal smooth muscle bundles may be present in the tunica adventitia, which is the most dominant layer in large
and some medium veins. The tunica adventitia is much thicker in the veins than the tunica media. For details, also see Table 9-1.
Exchange of gases, nutrients, and materials occurs in the capillaries. Three types of capillaries are illustrated here.
Continuous cap-
illaries
have complete endothelial cells and continuous basal laminae.
Fenestrated capillaries
have continuous basal laminae with
fenestrated endothelial cells (perforated by small pores);
discontinuous (sinusoidal) capillaries
have incomplete endothelial cells
perforated by large pores, and part of the cytoplasm may be missing. The basal lamina is discontinuous. Discontinuous capillaries
have gaps between endothelial cells, and their lumen sizes are much larger than the other two types. Blood vessel sizes are not drawn
to scale.
D. Cui /T. Yang
D. Cui /T. Yang
T. Yang
Large artery
(elastic artery)
Large vein
Medium artery
(muscular artery)
Medium vein
Small artery
Small vein
Arteriole
Venule
Continuous capillary
Fenestrated
capillary
Discontinuous (sinusoidal)
capillary
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