Page 776 - Fundamentals of anatomy physiology

Figure 21–8 Relationships among Vessel Diameter, Chapter 21 Blood Vessels and Circulation 763
Cross-Sectional Area, Blood Pressure, and Blood Velocity
within the Systemic Circuit. Figure 21–9 Pressures within the Systemic Circuit. Notice the

3 general reduction in circulatory pressure within the systemic circuit
and the elimination of the pulse pressure within the arterioles.

Systolic
120

2

Vessel 1 Pulse 100 Mean arterial
diameter pressure pressure

(cm) 80

0 Veins Venae 60 Diastolic
Elastic Muscular Arterioles Capillaries Venules cavae mm Hg
arteries arteries
40
Aorta a Vessel diameter

5000

4000

Cross- 3000 20
sectional

area 2000
(cm2)

1000 0

0 Elastic Muscular Arterioles Capillaries Venules Veins Venae Aorta
arteries arteries cavae Elastic
arteries
Aorta b Total cross-sectional area of vessels Muscular
arteries
Arterioles
Capillaries
Venules
Medium-
sized veins
Large veins
Venae cavae

120

100 Arterial Blood Pressure 21

80 Arterial pressure is important because it maintains blood flow
60
Average 40 through capillary beds. To do this, it must always be high
blood 20
enough to overcome the peripheral resistance. Arterial pres-
pressure
(mm Hg) sure is not constant. Rather, it rises during ventricular systole

and falls during ventricular diastole. The peak blood pressure

0 measured during ventricular systole is called systolic pressure,
Elastic Muscular Arterioles Capillaries Venules
arteries arteries Veins Venae and the minimum blood pressure at the end of ventricular
cavae
diastole is called diastolic pressure. In recording blood pres-
Aorta c Average blood pressure
sure, we separate systolic and diastolic pressures by a slash, as

in “120/80” (“one-twenty over eighty”) or “110/75.”

35 A pulse is a rhythmic fluctuation in pressure that accom-

Velocity 28 panies each heartbeat. The difference between the systolic and
of blood 21
14 diastolic pressures is the pulse pressure (Figure 21–9). To
flow
(cm/sec) report a single blood pressure value, we use the mean arterial

pressure (MAP). It is calculated by adding one-third of the

7 pulse pressure to the diastolic pressure:

0 Veins Venae MAP = diastolic pressure + pulse pressure
Elastic Muscular Arterioles Capillaries Venules cavae 3
arteries arteries

Aorta d Velocity of blood flow