Chapter 19
The Cardiovascular System: Blood Vessels
695
19
Elastic arteries are pressure reservoirs, expanding and re-
coiling as the heart ejects blood. Consequently, blood flows
fairly continuously rather than starting and stopping with the
pulsating rhythm of the heartbeat. If the blood vessels become
hard and unyielding, as in atherosclerosis, blood flows more
intermittently, similar to the way water flows through a hard
rubber garden hose attached to a faucet. When the faucet is
on, the high pressure makes the water gush out of the hose.
But when the faucet is shut off, the water flow abruptly be-
comes a trickle and then stops, because the hose walls can-
not recoil to keep the water under pressure. Also, without the
pressure-smoothing effect of the elastic arteries, the walls of
arteries throughout the body experience higher pressures.
Battered by high pressures, the arteries eventually weaken and
may balloon out or even burst. (Tese problems are discussed
in
A Closer Look
on pp. 700–701.)
Venous system
Large veins
(capacitance
vessels)
Large
lymphatic
vessels
Arterial system
Arteriovenous
anastomosis
Lymphatic
system
Lymphatic capillaries
Postcapillary
venule
Sinusoid
Metarteriole
Terminal
arteriole
Arterioles
(resistance
vessels)
Muscular
arteries
(distributing
arteries)
Elastic
arteries
(conducting
arteries)
Heart
Small veins
(capacitance
vessels)
Lymph
node
Capillaries
(exchange
vessels)
Precapillary
sphincter
Thoroughfare
channel
Figure 19.2
The relationship of blood vessels to each other and to lymphatic vessels.
Lymphatic vessels recover excess tissue fluid and return it to the blood.
Elastic Arteries
Elastic arteries
are the thick-walled arteries near the heart—the
aorta and its major branches. Tese arteries are the largest in
diameter, ranging from 2.5 cm to 1 cm, and the most elastic (±a-
ble 19.1). Because their large lumens make them low-resistance
pathways that conduct blood from the heart to medium-sized
arteries, elastic arteries are sometimes called
conducting arteries
(Figure 19.2).
Elastic arteries contain more elastin than any other vessel
type. It is present in all three tunics, but the tunica media con-
tains the most. Tere the elastin constructs concentric “holey”
sheets of elastic connective tissue that look like slices of Swiss
cheese sandwiched between layers of smooth muscle cells.
Although elastic arteries also contain substantial amounts of
smooth muscle, they are relatively inactive in vasoconstriction.
Tus, in terms of function, they can be visualized as simple elas-
tic tubes.
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