94
CARDIOVASCULAR PHYSIOLOGY CONCEPTS
Aorta
Vena
Cava
Distribution/Resistance
Exchange
Capacitance
■ FIGURE 5.1 Major types of blood vessels found w ithin the circulation.
The different types of vessels can be grouped
by
their
primary
function:
distribution/
resistance (aorta, large and small distributing
arteries), exchange (capillaries, small ven-
ules), and capacitance (large venules, veins,
vena cavae).
DISTRIBUTION/RESISTANCE VESSELS
The aorta, besides being the main vessel to
distribute blood from the heart to the arte-
rial system, dampens the pulsatile pressure
that results from the intermittent ejection of
blood from the left ventricle. The dampen-
ing is a function of the aortic compliance,
which is discussed in more detail later in this
chapter. Large arteries branching off the aorta
(e.g., carotid, mesenteric, and renal arteries)
distribute the blood flow to specific organs
or regions of the body. These large arteries,
although capable of constricting and dilating,
serve no significant role in the regulation of
pressure and blood flow under normal physi-
ologic conditions. Once the distributing artery
reaches the organ to which it supplies blood,
it branches into small arteries that distribute
blood flow within the organ. These smaller
arteries
continue
branching
into
smaller
and smaller vessels. Once they reach diam-
eters of <200 |j,m, they are termed arterioles.
No clear demarcation between small arteries
and arterioles exists; therefore, no consen-
sus has been reached regarding the point at
TABLE 5-1
SIZE AND FUNCTION OF DIFFERENT TYPES OF BLOOD VESSELS
IN THE SYSTEMIC CIRCULATION
V E S S E L T Y P E
1 D IA M E T E R (m m )
I F U N C T IO N
Aorta
25
Pulse dampening and distribution
Large arteries
1.0-10.0
Distribution
Small arteries
0.2-1.0
Distribution and resistance
Arterioles
0.01-0.20
Resistance (pressure/flow regulation)
Capillaries
0.006-0.010
Exchange
Venules
0.01-0.20
Exchange, collection, and capacitance
Veins
0.2-10.0
Capacitance function (blood volume)
Vena cava
35
Collection
previous page 107 Cardiovascular Physiology Concepts  2nd Edition read online next page 109 Cardiovascular Physiology Concepts  2nd Edition read online Home Toggle text on/off