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Chapter 21
Peripheral Circulation &
Regulation
• The heart is the pump that provides the major force
causing blood to circulate and the blood vessels are the
pipes that carry the blood to the tissues of the body and
back to the heart
2 major vessel types:
1. Systemic Vessels:
–
Transport blood from left ventricle to the body back to right atrium
2. Pulmonary Vessels:
–
Transport blood from the right ventricle to the lungs back to the
left atrium
AP2 Chap. 21: Cardio Syst-Vessels
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I. Functions of peripheral
circulation
AP2 Chap. 21: Cardio Syst-Vessels
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I. Fxns of peripheral circulation
5 major fxns:
1.
Carries blood
–
2.
XD’s nutrients, waste products, & gases w/tissues
–
–
3.
Not only the nutrients & wastes but things like hormones &
immune system components
Helps to regulate BP
–
5.
Nutrients & O2 can diffuse from blood to cells
Wastes & CO2 can diffuse from cells to blood
Transports substances
–
4.
Takes blood on a roundtrip from heart to tissues back to heart
Using contractions of smooth muscle to make vessels larger or
smaller
Directs blood flow to tissues
–
It can flow with purpose directing circulation to areas in need.
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
A. Laminar & turbulent flow in vessels
B. BP
C. Blood flow & Poiseuille’s Law
D. Critical closing pressure & Laplace’s Law
E. Vascular Compliance
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
• Just like water flowing thru pipes certain
relationships effect the function of the
cardiovascular system these include:
– BP
– Flow
– Resistance
– Control mechanisms of BP & blood flow
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
A. Laminar & turbulent flow in vessels
• Laminar flow: fluid in a smooth
tube moves in a stream lined
fashion
• It flows in concentric layers.
Because the outmost blood is
against the stationary wall of
the vessel, it moves slowest;
but as the layers go inward they
become faster with the
innermost fasted.
• Turbulent flow: when a rate of
flow exceeds a critical velocity
or when fluid passes a
constriction, sharp turn, or
rough surface.
• The vibrations caused by the
chaotic blood flow cause sound
(Some sounds thru valves in
heart or BP cuff) Abnormal
sounds can signal a blocked
artery
Figure 21.31
Page 741
6
VI. The dynamics of blood circulation
B. Blood Pressure
• BP measure of the force bld
exerts on the blood vessel walls
• 2 main methods for measuring:
– Mercury Manometer
• Indirect
– Cannula
• Direct (tube inserted directly into the
blood vessel)
• Although 2 methods exist, using
a stethoscope (auscultatory
methods) are more practical in a
clinical setting.
• Korotkoff Sounds: point at which
cuff loosens enough to allow for
turbulent flow in the artery
(represents systolic pressure #)
• Diastolic Pressure #: when
sounds are no longer heard
Figure 21.32
Page 742
7
B. Blood Pressure
VI. The dynamics of blood circulation
Figure 21.31
Page
753 21.32
Figure
Page 742
AP2 Chap. 21: Cardio Syst-Vessels
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VI. Dynamics of Blood Circulation
Poiseuille’s Law
Laplace’s Law:
• a small D in radius dramatically
D’s resistance to flow thus the
amount of blood flowing thru
the vessel
• The force acting on the wall of
a blood vessel is proportional
to the diameter of the vessel
times BP
AP2 Chap. 19: Cardiovascular Syst
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VI. The dynamics of blood circulation
C. Bld Flow & Poiseuille’s (pwah-zuh’yes) Law
• Blood flow: amount of
bld that moves thru a
vessel in a given period
– Blood flow is directly
proportional to pressure
differences
• BP  = Bld flow 
– Blood flow is inversely
proportional to resistance
• Resistance: sum of
all factors that inhibit
bld flow
– Effected by:
• D’s in viscosity
• D’s in bld vessel
diameter
• D’s in bld vessel length
• Resistance  = bld flow 
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
C. Bld Flow & Poiseuille’s (pwah-zuh’yes)
Law
• Viscosity: resistance
of a liquid to flow
• Bld’s viscosity is the
result of [RBC]. As
hematocrit (% of
total bld vol.
composed of RBC’s)
increases so does bld
viscosity
• Poiseuille’s Law
states that a small D
in radius dramatically
D’s resistance to flow
thus the amount of
blood flowing thru the
vessel.
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
D. Critical Closing Pressure & Laplace’s Law
• As pressure in a vessel
, the force holding the
vessel open , & the
vessel tends to collapse.
• Critical Closing
Pressure:
– Pressure at which the
blood vessel closes and
blood flow stops
• Laplace’s Law:
– The force acting on
the wall of a blood
vessel is proportional
to the diameter of the
vessel times BP
F= force
D= diameter
P= pressure
F=D*P
• Shock (BP drops) necrosis
• Aneurysm
AP2 Chap. 21: Cardio Syst-Vessels
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VI. The dynamics of blood circulation
E. Vascular Compliance
• Compliance:
• Veins:
– Tendency for blood
vessel vol to  as the
BP 
• Vessels with a high
compliance exhibit
large increases in
volume when pressure
increases a small
amount. (vise versa)
– 24X greater compliance
than arteries
– Thus veins can act as
storage areas
(reservoirs) for blood
because high
compliance allows them
to hold larger volume
than other areas of the
vascular system
AP2 Chap. 21: Cardio Syst-Vessels
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VII. Physiology of Systemic Circulation
A.
B.
C.
D.
Cross sectional area
Pressure & resistance
Pulse Pressure
Capillary XD & regulation of
interstial fluid
E. Fxnal characteristics of veins
F. BP & FX of gravity
AP2 Chap. 21: Cardio Syst-Vessels
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VII. Physiology of Systemic Circulation
• Physiological characteristics
of the circulatory system are
determined by:
– Anatomy of circulatory system
– Dynamics of blood flow
– Regulatory mechanisms of the
heart & blood vessels
• 84% of blood resides in the
systemic blood vessels
– 64% in the systemic veins
– 15% in systemic arteries
– 5% in capillaries
AP2 Chap. 21: Cardio Syst-Vessels
Page 743
15
VII. Physiology of Systemic Circulation
A. Cross-sectional area of blood vessels
• As the diameter of blood
vessels decreases their total
cross-sectional area (CSA)
increases and the velocity of
blood flow thru them
decreases
Aorta= 5 cm2 cross sectional area
Capillaries (each with a very small cross
sectional area) The total cross sectional
area of ALL capillaries = 2500 cm2
Thus the smaller vessels have more
area
Velocity of blood flow is greatest in the
aorta but total CSA is small. Velocity of
blood flow is low in capillaries, but the
total CSA is large.
Figure 21.33
Page 744
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VII. Physiology of Systemic Circulation
B. Pressure & resistance
• BP is initially 100mmHg in the
aorta ending at 0mmHg in the
right atrium (high to low
movement)
• Decreases in arterial pressure
are directly proportional to
resistance. With the highest
encountered at the arterioles.
– When it gets there 85mmHg at
the end 35mmHg
– Also fairly high resistance in the
capillaries
Figure 21.33 Page 756
Figure 21.34
Page 745
• Low resistance in veins b/c they
have a relatively large diameter.
• Arteries can contract or relax
changing their diameter &
pressure
AP2 Chap. 21: Cardio Syst-Vessels
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VII. Physiology of Systemic Circulation
C. Pulse Pressure
• Pulse pressure equals the
difference between the
systolic & diastolic
pressures
– Increases when:
• Stroke volume increases
• Vascular compliance
decreases
Pg 746
Fig 21.35
• Pulse pressure waves
travel thru the vascular
system faster than blood
flows. PP can be used to
take a pulse as the artery
expands with the PP
waves. (radial pulse)
AP2 Chap. 21: Cardio Syst-Vessels
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VII. Physiology of Systemic Circulation
D. Capillary XD & regulation of interstitial fluid
volume
• 3 things affect the movement
of fluid from the capillaries:
– BP
– Capillary Permeability
– Osmosis
• Net movement occurs
from the blood vessel into
the tissues. The
lymphatic system
removes XS tissue fluid.
• Capillary XD
– Mvmt of substances into & out
of the capillary
– Most important method used is
diffusion
• Nutrients, gases & hormones
• Some go thru fenestrations
others between the cell spaces.
• Pinocytosis does a very small
amount
AP2 Chap. 21: Cardio Syst-Vessels
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VII. Physiology of Systemic Circulation
Fxnal Characteristics of Veins
• Factors that increase
venous return to the heart
include:
a) Increase in blood volume
b) Venous tone (constriction
or dilation of the veins)
•
BP & the effect of gravity
• Hydrostatic pressure
caused by gravity
increases BP below the
level of the heart &
decreases BP above the
level of the heart.
Based on SNS
stimulation
c) Arteriole dilation
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
A. Local control of blood flow by the tissues
B. Nervous & hormonal regulation of local
circulation
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the
tissues
• Blood flow to the tissues is highly
controlled and matched closely to the
metabolic needs of tissues.
• 2 mechanisms of control are:
A. Local Control
•
•
•
Fxnal characteristics of the capillary bed
Autoregulation of blood flow
Long-term local blood flow
B. Nervous & hormonal control
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
A. Local control of blood flow by tissues
• Blood flow can vary by
organ with some getting
more than others with
little change.
• Some tissues alter
blood flow based on
metabolic need such as
skeletal muscle at rest
vs. exercising (20X
more flow than at rest).
• Blood serves to deliver
nutrients & remove
waste, but:
– Skin: blood flow
dissipates heat
– Kidneys: eliminated
metabolic waste
products, regulates
water balance, controls
pH of body fluids
– Small intestine: blood
removes the nutrients for
liver processing
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
A. Local control of blood flow by tissues
Fxnal Characteristics of the capillary bed
• Capillaries can alter blood flow based on the conditions of the tissues
they supply
– Vasomotion: cyclic fluctuation of contraction & relaxation of sphincters
• Vasodilator substances are prod’d as metabolism increases. They
literally diffuse from the tissue to the precapillary sphincter muscles to
get them to relax.
Pg 751
Fig 21.37
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
A. Local control of blood flow by tissues
Autoregulation of Blood Flow
• Arterial BP can D over
a wide range, but
blood flow remains
relatively constant.
• Autoregulation is
maintenance of blood
flow by the tissues
themselves.
In the tissues:
• Build-up of metabolic
waste
– Precapillary sphincters
dilate
• Blood flow increases
• Nutrient & O2 supply
adequate
– Precapillary sphincters
constrict
• Blood flow decreases
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
A. Local control of blood flow by tissues
Long term regulation
• Long term regulation of blood flow is
matched to the metabolic needs of the
tissue.
• Metabolic activity in tissue increases over
long term:
– Diameter & # of blood vessels increase 
• Results in increase in local blood flow.
AP2 Chap. 21: Cardio Syst-Vessels
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VIII. Control of Blood Flow in the tissues
B. Nervous & hormonal regulation of local circulation
• NS control of Arterial BPimportant in the minute-tominute regulation of local
circulation
• SNS (vasomotor center of the
medulla oblongata) controls
blood vessel diameter and can
be influenced by other areas in
the brain.
• Vasomotor Tone: state of partial
contraction of blood vessels
• NS is responsible for routing
the flow of blood & maintaining
BP
• SNS action potentials stimulate
adrenal medulla to release epi
& norepi which cause
vasoconstriction of most blood
vessels (Skeletal muscle is
opposite)
AP2 Chap. 21: Cardio Syst-Vessels
Figure 21.38
pg 752
27
IX. Regulation of Mean Arterial BP
A. Short term regulation
B. Long term regulation
AP2 Chap. 21: Cardio Syst-Vessels
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IX. Regulation of Mean Arterial BP
• MAP: proportional to cardiac output times
peripheral resistance
MAP= CO * PR or HR * SV * PR
Heart rate = HR
Stroke volume= SV
• Thus an increase in CO, PR, HR, or SV
increases MAP or vise versa
• 2 major control systems to maintain
homeostasis:
A. Short term
•
Respond quickly but can’t maintain for longer than a few
days
B. Long term
•
Primarily mechanisms that influence kidney fxn
AP2 Chap. 21: Cardio Syst-Vessels
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Regulation of MAP
• Short Term reg of
BP
– Baroreceptor Reflex
– Adrenal Medullary
Mechanism
– Chemoreceptor
Reflexes
– CNS Ischemic
Response
• Long Term reg of BP
– Renin-angiotensinaldosterone
Mechanism
– ADH mechanism
– Atrial Natriuretic
Mechanism
– Fluid Shift Mechanism
– Stress relaxation
response
AP2 Chap. 21: Cardio Syst-Vessels
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Baroreceptor Reflex
• Minute to minute monitoring of small changes in BP
that respond quickly
Figure 21.39
pg 754
AP2 Chap. 21: Cardio Syst-Vessels
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Baroreceptor Reflex
Figure 21.40
Page 755
AP2 Chap. 21: Cardio Syst-Vessels
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Adrenal Regulatory Mechanism
• Physical activity/ stress
• Stimulation of Medulla
oblongata
Figure 21.41
Page 756
– Signal to SNS to adrenal
medulla
• Releases Epi & norepi
• Result:
– Increased HR, SV,
vasoconstriction of blood
vessels to skin &
viscera, and
vasodilatation of blood
vessels to heart
AP2 Chap. 21: Cardio Syst-Vessels
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Chemoreceptors
Figures 21.42
Page 757
AP2 Chap. 21: Cardio Syst-Vessels
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Chemoreceptors
Figure 21.43
Page 758
AP2 Chap. 21: Cardio Syst-Vessels
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CNS Ischemic Response
• Elevation of BP in response to lack of
blood flow to the medulla oblongata
– Causes high CO2 & low pH levels
• Responds to emergency situations where
brain is starving for O2
• Vasomotor center is stimulated 
stimulates vasoconstriction systemic BP
rises (provided blood vessels are intact)
AP2 Chap. 21: Cardio Syst-Vessels
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Regulation of MAP
• Short Term reg of BP
– Baroreceptor Reflex
– Adrenal Medullary
Mechanism
– Chemoreceptor
Reflexes
– CNS Ischemic
Response
• Long Term reg of BP
– Renin-angiotensinaldosterone
Mechanism
– ADH mechanism
– Atrial Natriuretic
Mechanism
– Fluid Shift
Mechanism
– Stress relaxation
response
AP2 Chap. 21: Cardio Syst-Vessels
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Long term regulation
• Regulation of the [ ] & volume of blood by
the kidneys, mvmt of fluid across blood
vessel walls, & alterations in the volume of
the blood vessels.
• Response is in minutes but maintenance
can last for hours, days, longer
AP2 Chap. 21: Cardio Syst-Vessels
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Renin-angiotensin-aldosterone Mechanism
Figure 21.44
Page 760
•Decreased BP
detected by kidney,
results in renin
secretion
•Result:
•Vasoconstriction
•Increased H2O
absorption
•Decreased urine
volume
•Maintains BP
AP2 Chap. 21: Cardio Syst-Vessels
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Vasopressin (ADH) mechanism
Figure 21.45 pg. 761
Increases in osmolarity of
blood or decreases in BP
result in ADH secretion.
Increases H2O
reabsorption by kidney, &
large amounts result in
vasoconstriction. Helps
maintain BP
AP2 Chap. 21: Cardio Syst-Vessels
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Summary of control of BP long term
mechanisms
Page 764
Figures 21.46
41
Long term regulation of BP
Fluid Shift mechanism
• Causes fluid to move
from the interstitial
spaces into the capillaries
in response to a decrease
in BP.
• Attempt to maintain blood
volume
Stress-relaxation response
• An adjustment of smooth
muscles of blood vessels
in response to change in
blood volume.
AP2 Chap. 21: Cardio Syst-Vessels
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