577
CHAPTER FIFTEEN
Cardiovascular System
FIGURE 15.27
Some metarterioles provide arteriovenous shunts by connecting arterioles directly to venules.
Metarteriole
(forming
arteriovenous
shunt)
Venule
Precapillary
sphincter
Arteriole
Artery
Blood flow
Blood flow
Vein
Capillaries
Slit
Capillary
(a)
Tissue fluid
Tissue fluid
Endothelial cell
Nucleus of
endothelial
cell
Endothelial
cell cytoplasm
Lumen of
capillary
Cell junction
(b)
(c)
FIGURE 15.28
Capillary structure. (
a
) Substances are exchanged
between the blood and tissue f
uid through openings (slits) separating
endothelial cells. (
b
) Transmission electron micrograph oF a capillary
cross section (11,500
×
).
(
c
) Note the narrow slitlike openings at the cell
junctions (arrow) (micrograph
b
enlarged to 62,500
×
).
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