Copyright © 2006 by Elsevier, Inc.. Components of the Circulation Figure 14-1; Guyton and Hall.

Copyright © 2006 by Elsevier, Inc.

.

Components of the Circulation

Figure 14-1; Guyton and Hall


The Capillaries Have the Largest Total Cross-sectional Area of the Circulation

cm2

Aorta 2.5Small Arteries 20Arterioles 40Capillaries 2500Venules 250Small Veins 80Venae Cavae 8


Velocity of Blood Flow is Greatest in the Aorta

Velocity of Blood Flow = Blood Flow Cross sectional area

Aorta >Arterioles> Small veins >Capillaries


.

The Majority of Blood Volume is in the Veins



Blood Pressure Profile in the Circulatory System

Systemic Pulmonary

Aor

ta

Lar

ge a

rter

ies

Smal

l art

erie

s

Art

erio

les

Cap

illa

ries

Pre

ssu

re(m

mH

g)

0

20

40

60

80

100

120

Ven

ule

s

Smal

l vie

ns

Lar

ge v

ien

s

Ven

ae c

avae

Pu

lmon

ary

arte

ries

Art

erio

les

Cap

illa

ries

Ven

ule

s

Pu

lmon

ary

vien

s

• High pressures in the arterial tree• Low pressures in the venous side of the circulation• Large pressure drop across the arteriolar-capillary junction


Variations in Tissue Blood Flow

Brain 14 700Heart 4 200Bronchi 2 100Kidneys 22 1100Liver 27 1350 Portal (21) (1050) Arterial (6) (300)Muscle (inactive state) 15 750Bone 5 250Skin (cool weather) 6 300Thyroid gland 1 50Adrenal glands 0.5 25Other tissues 3.5 175

Total 100.0 5000

Percent ml/min


Characteristics of Blood Flow

– When laminar flow occurs, the velocity of blood in the center of the vessel is greater than that toward the outer edge creating a parabolic profile.

Blood Vessel

Laminar flow


Laminar Vs. Turbulent Blood Flow

Turbulent flow

• Laminar flow is silent, whereas turbulent flow tend to cause murmurs.

• Murmurs or bruits are important in diagnosing vessels stenosis, vessel shunts, and cardiac valvular lesions.


Effect of Wall Stress on Blood Vessels

Turbulent flow increases wall stress


Parallel and Serial Resistance Sites in the Circulation


Effect of Vessel Diameter on Blood Flow

• Conductance is very sensitive to change in diameter of vessel.

• The conductance of a vessel increases in proportion to the fourth power of the radius.



Determinants of Blood Flow

FLOW = arterial - venous pressure (P)resistance (R)

FLOW = 100 - 0 mmHg.1 mmHg/ml/min

FLOW = 100 - 20 mmHg.1 mmHg/ml/min

FLOW = 1000 ml/min FLOW = 800 ml/min

100 mmHg

0 mmHg 20 mmHg

100 mmHg

R = .1mmHg/ml/min R = .1mmHg/ml/min

A B


How Would a Decrease in Vascular Resistance Affect Blood Flow?

FLOW = P RESISTANCE

FLOW = P RESISTANCE

Conversely,


Hematocrit and Viscosity Effects on Blood Flow

Figure 14-11; Guyton and Hall Figure 14-12; Guyton and Hall


Arterial Pulsations

• The height of the pressure pulse is the systolic pressure (120mmHg), while the lowest point is the diastolic pressure (80mmHg).

• The difference between systolic and diastolic pressure is called the pulse pressure (40mmHg).

Systolic Pressure

Diastolic Pressure

Pulse Pressure}


Damping of Pulse Pressuresin the Peripheral Arteries



DiastolicPressure

Systolic PressureCardiac output

Peripheral resistance

Mean Pressure

Time

Pre

ssu

re

Stroke volume

Arterial compliance

}Pulse Pressure

Arterial Pulse


Abnormal Pressure Pulse Contours



Pulse Pressure and Age



Cuff Pressure < 80

Cuff Pressure > 120

NO FLOW

FREE FLOW

Effect of Cuff Pressure on Brachial Blood Flow


Measurement of Blood Pressure

Use of Korotkoff Sounds

120 100 80

150

100

50

0

Copyright © 2006 by Elsevier, Inc.. Components of the Circulation Figure 14-1; Guyton and Hall.

Documents

Transcript of Copyright © 2006 by Elsevier, Inc.. Components of the Circulation Figure 14-1; Guyton and Hall.