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PowerPoint® Lecture Slides
prepared by
Barbara Heard,
Atlantic Cape Community
Ninth Edition
College
Human Anatomy & Physiology
CHAPTER
19
The
Cardiovascular
System: Blood
Vessels: Part A
© Annie Leibovitz/Contact Press Images
© 2013 Pearson Education, Inc.
Structure of Blood Vessel Walls
• Lumen
– Central blood-containing space
• Three wall layers in arteries and veins
– Tunica intima, tunica media, and tunica
externa
• Capillaries
– Endothelium with sparse basal lamina
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Figure 19.1b Generalized structure of arteries, veins, and capillaries.
Tunica intima
• Endothelium
• Subendothelial layer
• Internal elastic membrane
Tunica media
(smooth muscle and
elastic fibers)
• External elastic membrane
Valve
Tunica externa
(collagen fibers)
• Vasa vasorum
Lumen
Lumen
Artery
Capillary network
Vein
Basement membrane
Endothelial cells
Capillary
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Tunics
• Tunica intima
– Endothelium lines lumen of all vessels
• Continuous with endocardium
• Slick surface reduces friction
– Subendothelial layer in vessels larger than
1 mm; connective tissue basement membrane
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Tunics
• Tunica media
– Smooth muscle and sheets of elastin
– Sympathetic vasomotor nerve fibers control
vasoconstriction and vasodilation of
vessels
• Influence blood flow and blood pressure
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Tunics
• Tunica externa (tunica adventitia)
– Collagen fibers protect and reinforce; anchor
to surrounding structures
– Contains nerve fibers, lymphatic vessels
– Vasa vasorum of larger vessels nourishes
external layer
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Figure 19.2 The relationship of blood vessels to each other and to lymphatic vessels.
Venous system
Large veins
(capacitance
vessels)
Arterial system
Heart
Elastic
arteries
(conducting
arteries)
Large
lymphatic
vessels
Lymph
node
Lymphatic
system
Small veins
(capacitance
vessels)
Muscular
arteries
(distributing
arteries)
Arteriovenous
anastomosis
Lymphatic
capillaries
Sinusoid
Arterioles
(resistance
vessels)
Terminal
arteriole
Postcapillary
venule
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Thoroughfare
channel
Capillaries
(exchange
vessels)
Precapillary
sphincter
Metarteriole
Arterial System: Elastic Arteries
• Large thick-walled arteries with elastin in
all three tunics
• Aorta and its major branches
• Large lumen offers low resistance
• Inactive in vasoconstriction
• Act as pressure reservoirs—expand and
recoil as blood ejected from heart
– Smooth pressure downstream
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Arterial System: Muscular Arteries
• Distal to elastic arteries
– Deliver blood to body organs
• Thick tunica media with more smooth
muscle
• Active in vasoconstriction
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Arterial System: Arterioles
• Smallest arteries
• Lead to capillary beds
• Control flow into capillary beds via
vasodilation and vasoconstriction
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Table 19.1 Summary of Blood Vessel Anatomy (1 of 2)
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Capillaries
• Microscopic blood vessels
• Walls of thin tunica intima
– In smallest one cell forms entire
circumference
• Pericytes help stabilize their walls and
control permeability
• Diameter allows only single RBC to pass
at a time
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Capillaries
• In all tissues except for cartilage, epithelia,
cornea and lens of eye
• Provide direct access to almost every cell
• Functions
– Exchange of gases, nutrients, wastes,
hormones, etc., between blood and interstitial
fluid
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Capillaries
• Three structural types
1. Continuous capillaries
2. Fenestrated capillaries
3. Sinusoid capillaries (sinusoids)
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Continuous Capillaries
• Abundant in skin and muscles
– Tight junctions connect endothelial cells
– Intercellular clefts allow passage of fluids and
small solutes
• Continuous capillaries of brain unique
– Tight junctions complete, forming blood brain
barrier
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Figure 19.3a Capillary structure.
Pericyte
Red blood
cell in lumen
Intercellular
cleft
Endothelial
cell
Basement
membrane
Tight junction
Endothelial
nucleus
Pinocytotic
vesicles
Continuous capillary. Least permeable, and most
common (e.g., skin, muscle).
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Fenestrated Capillaries
• Some endothelial cells contain pores
(fenestrations)
• More permeable than continuous
capillaries
• Function in absorption or filtrate formation
(small intestines, endocrine glands, and
kidneys)
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Figure 19.3b Capillary structure.
Pinocytotic
vesicles
Red blood
cell in lumen
Fenestrations
(pores)
Endothelial
nucleus
Basement membrane
Tight junction
Intercellular
cleft
Endothelial
cell
Fenestrated capillary. Large fenestrations (pores)
increase permeability. Occurs in areas of active
absorption or filtration (e.g., kidney, small intestine).
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Sinusoid Capillaries
• Fewer tight junctions; usually fenestrated;
larger intercellular clefts; large lumens
• Blood flow sluggish – allows modification
– Large molecules and blood cells pass
between blood and surrounding tissues
• Found only in the liver, bone marrow,
spleen, adrenal medulla
• Macrophages in lining to destroy bacteria
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Figure 19.3c Capillary structure.
Endothelial
cell
Red blood
cell in lumen
Large
intercellular
cleft
Tight junction
Incomplete
basement
membrane
Nucleus of
endothelial
cell
Sinusoid capillary. Most permeable. Occurs in special
locations (e.g., liver, bone marrow, spleen).
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Capillary Beds
• Microcirculation
– Interwoven networks of capillaries between
arterioles and venules
– Terminal arteriole  metarteriole
– Metarteriole continuous with thoroughfare
channel (intermediate between capillary and
venule)
– Thoroughfare channel  postcapillary
venule that drains bed
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Capillary Beds: Two Types of Vessels
• Vascular shunt (metarteriole—
thoroughfare channel)
– Directly connects terminal arteriole and
postcapillary venule
• True capillaries
– 10 to 100 exchange vessels per capillary bed
– Branch off metarteriole or terminal arteriole
© 2013 Pearson Education, Inc.
Blood Flow Through Capillary Beds
• True capillaries normally branch from
metarteriole and return to thoroughfare
channel
• Precapillary sphincters regulate blood
flow into true capillaries
– Blood may go into true capillaries or to shunt
• Regulated by local chemical conditions
and vasomotor nerves
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Figure 19.4 Anatomy of a capillary bed.
Precapillary sphincters
Vascular shunt
Metarteriole Thoroughfare
channel
True
capillaries
Terminal arteriole
Postcapillary venule
Sphincters open—blood flows through true capillaries.
Terminal arteriole
Postcapillary venule
Sphincters closed—blood flows through metarteriole – thoroughfare
channel and bypasses true capillaries.
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Venous System: Venules
• Formed when capillary beds unite
– Smallest postcapillary venules
– Very porous; allow fluids and WBCs into
tissues
– Consist of endothelium and a few pericytes
• Larger venules have one or two layers of
smooth muscle cells
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Figure 19.5 Relative proportion of blood volume throughout the cardiovascular system.
Pulmonary blood
vessels 12%
Systemic arteries
and arterioles 15%
Heart 8%
Capillaries 5%
Systemic veins
and venules 60%
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Veins
• Adaptations ensure return of blood to
heart despite low pressure
– Large-diameter lumens offer little resistance
– Venous valves prevent backflow of blood
• Most abundant in veins of limbs
– Venous sinuses: flattened veins with
extremely thin walls (e.g., coronary sinus of
the heart and dural sinuses of the brain)
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Table 19.1 Summary of Blood Vessel Anatomy (2 of 2)
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Figure 19.1a Generalized structure of arteries, veins, and capillaries.
Artery
Vein
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Vascular Anastomoses
• Interconnections of blood vessels
• Arterial anastomoses provide alternate
pathways (collateral channels) to given
body region
– Common at joints, in abdominal organs, brain,
and heart; none in retina, kidneys, spleen
• Vascular shunts of capillaries are
examples of arteriovenous anastomoses
• Venous anastomoses are common
© 2013 Pearson Education, Inc.
Physiology of Circulation: Definition of
Terms
• Blood flow
– Volume of blood flowing through vessel,
organ, or entire circulation in given period
• Measured as ml/min
• Equivalent to cardiac output (CO) for entire
vascular system
• Relatively constant when at rest
• Varies widely through individual organs, based on
needs
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Physiology of Circulation: Definition of
Terms
• Blood pressure (BP)
– Force per unit area exerted on wall of blood
vessel by blood
• Expressed in mm Hg
• Measured as systemic arterial BP in large arteries
near heart
– Pressure gradient provides driving force that
keeps blood moving from higher to lower
pressure areas
© 2013 Pearson Education, Inc.
Physiology of Circulation: Definition of
Terms
• Resistance (peripheral resistance)
– Opposition to flow
– Measure of amount of friction blood
encounters with vessel walls, generally in
peripheral (systemic) circulation
• Three important sources of resistance
– Blood viscosity
– Total blood vessel length
– Blood vessel diameter
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Resistance
• Factors that remain relatively constant:
– Blood viscosity
• The "stickiness" of blood due to formed elements
and plasma proteins
• Increased viscosity = increased resistance
– Blood vessel length
• Longer vessel = greater resistance encountered
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Resistance
• Blood vessel diameter
– Greatest influence on resistance
• Frequent changes alter peripheral
resistance
• Varies inversely with fourth power of
vessel radius
– E.g., if radius is doubled, the resistance is
1/16 as much
– E.g., Vasoconstriction  increased resistance
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Resistance
• Small-diameter arterioles major
determinants of peripheral resistance
• Abrupt changes in diameter or fatty
plaques from atherosclerosis dramatically
increase resistance
– Disrupt laminar flow and cause turbulent flow
• Irregular fluid motion  increased resistance
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Relationship Between Blood Flow, Blood
Pressure, and Resistance
• Blood flow (F) directly proportional to
blood pressure gradient ( P)
– If  P increases, blood flow speeds up
• Blood flow inversely proportional to
peripheral resistance (R)
– If R increases, blood flow decreases:
F =  P/R
• R more important in influencing local blood
flow because easily changed by altering
blood vessel diameter
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Systemic Blood Pressure
• Pumping action of heart generates blood
flow
• Pressure results when flow is opposed by
resistance
• Systemic pressure
– Highest in aorta
– Declines throughout pathway
– 0 mm Hg in right atrium
• Steepest drop occurs in arterioles
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Figure 19.6 Blood pressure in various blood vessels of the systemic circulation.
120
Systolic pressure
100
Mean pressure
80
60
40
Diastolic
pressure
20
0
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Arterial Blood Pressure
• Reflects two factors of arteries close to
heart
– Elasticity (compliance or distensibility)
– Volume of blood forced into them at any time
• Blood pressure near heart is pulsatile
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Arterial Blood Pressure
• Systolic pressure: pressure exerted in
aorta during ventricular contraction
– Averages 120 mm Hg in normal adult
• Diastolic pressure: lowest level of aortic
pressure
• Pulse pressure = difference between
systolic and diastolic pressure
– Throbbing of arteries (pulse)
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Arterial Blood Pressure
• Mean arterial pressure (MAP): pressure
that propels blood to tissues
• MAP = diastolic pressure + 1/3 pulse
pressure
• Pulse pressure and MAP both decline with
increasing distance from heart
• Ex. BP = 120/80; MAP = 93 mm Hg
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Capillary Blood Pressure
• Ranges from 17 to 35 mm Hg
• Low capillary pressure is desirable
– High BP would rupture fragile, thin-walled
capillaries
– Most very permeable, so low pressure forces
filtrate into interstitial spaces
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Venous Blood Pressure
• Changes little during cardiac cycle
• Small pressure gradient; about 15 mm Hg
• Low pressure due to cumulative effects of
peripheral resistance
– Energy of blood pressure lost as heat during
each circuit
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Factors Aiding Venous Return
1. Muscular pump: contraction of skeletal
muscles "milks" blood toward heart;
valves prevent backflow
2. Respiratory pump: pressure changes
during breathing move blood toward
heart by squeezing abdominal veins as
thoracic veins expand
3. Venoconstriction under sympathetic
control pushes blood toward heart
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Figure 19.7 The muscular pump.
Venous valve (open)
Contracted skeletal
muscle
Venous valve
(closed)
Vein
Direction of blood flow
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Maintaining Blood Pressure
• Requires
– Cooperation of heart, blood vessels, and
kidneys
– Supervision by brain
• Main factors influencing blood pressure
– Cardiac output (CO)
– Peripheral resistance (PR)
– Blood volume
© 2013 Pearson Education, Inc.
Maintaining Blood Pressure
• F =  P/R; CO =  P/R;  P = CO × R
• Blood pressure = CO × PR (and CO
depends on blood volume)
• Blood pressure varies directly with CO,
PR, and blood volume
• Changes in one variable quickly
compensated for by changes in other
variables
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Cardiac Output (CO)
• CO = SV × HR; normal = 5.0-5.5 L/min
• Determined by venous return, and neural
and hormonal controls
• Resting heart rate maintained by
cardioinhibitory center via parasympathetic
vagus nerves
• Stroke volume controlled by venous return
(EDV)
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Cardiac Output (CO)
• During stress, cardioacceleratory center
increases heart rate and stroke volume via
sympathetic stimulation
– ESV decreases and MAP increases
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Figure 19.8 Major factors enhancing cardiac output.
Exercise
BP activates cardiac centers in medulla
Activity of respiratory pump
(ventral body cavity pressure)
Sympathetic activity
Parasympathetic activity
Activity of muscular pump
(skeletal muscles)
Epinephrine in blood
Sympathetic venoconstriction
Venous return
Contractility of cardiac muscle
ESV
EDV
Stroke volume (SV)
Heart rate (HR)
Initial stimulus
Physiological response
Result
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Cardiac output (CO = SV x HR)
Control of Blood Pressure
• Short-term neural and hormonal controls
– Counteract fluctuations in blood pressure by
altering peripheral resistance and CO
• Long-term renal regulation
– Counteracts fluctuations in blood pressure by
altering blood volume
© 2013 Pearson Education, Inc.
Short-term Mechanisms: Neural Controls
• Neural controls of peripheral resistance
– Maintain MAP by altering blood vessel
diameter
• If low blood volume all vessels constricted except
those to heart and brain
– Alter blood distribution to organs in response
to specific demands
© 2013 Pearson Education, Inc.
Short-term Mechanisms: Neural Controls
• Neural controls operate via reflex arcs
that involve
– Baroreceptors
– Cardiovascular center of medulla
– Vasomotor fibers to heart and vascular
smooth muscle
– Sometimes input from chemoreceptors and
higher brain centers
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The Cardiovascular Center
• Clusters of sympathetic neurons in medulla
oversee changes in CO and blood vessel
diameter
• Consists of cardiac centers and vasomotor
center
• Vasomotor center sends steady impulses via
sympathetic efferents to blood vessels 
moderate constriction called vasomotor tone
• Receives inputs from baroreceptors,
chemoreceptors, and higher brain centers
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Short-term Mechanisms: Baroreceptor
Reflexes
• Baroreceptors located in
– Carotid sinuses
– Aortic arch
– Walls of large arteries of neck and thorax
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Short-term Mechanisms: Baroreceptor
Reflexes
• Increased blood pressure stimulates
baroreceptors to increase input to
vasomotor center
– Inhibits vasomotor and cardioacceleratory
centers, causing arteriolar dilation and
venodilation
– Stimulates cardioinhibitory center
–  decreased blood pressure
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Short-term Mechanisms: Baroreceptor
Reflexes
• Decrease in blood pressure due to
– Arteriolar vasodilation
– Venodilation
– Decreased cardiac output
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Short-term Mechanisms: Baroreceptor
Reflexes
• If MAP low
–  Reflex vasoconstriction  increased CO 
increased blood pressure
– Ex. Upon standing baroreceptors of carotid
sinus reflex protect blood to brain; in
systemic circuit as whole aortic reflex
maintains blood pressure
• Baroreceptors ineffective if altered blood
pressure sustained
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Figure 19.9 Baroreceptor reflexes that help maintain blood pressure homeostasis.
3
Impulses from baroreceptors
stimulate cardioinhibitory center
(and inhibit cardioacceleratory
center) and inhibit vasomotor
center.
4a
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
2 Baroreceptors
in carotid sinuses
and aortic arch
are stimulated.
4b
Rate of
vasomotor impulses
allows vasodilation,
causing R.
1 Stimulus:
Blood pressure
(arterial blood
pressure rises
above normal
range).
5 CO and R
return blood
pressure to
homeostatic range.
1 Stimulus:
5 CO and R return
blood pressure to
homeostatic range.
Blood pressure
(arterial blood
pressure falls below
normal range).
4b Vasomotor
fibers stimulate
vasoconstriction,
causing R.
2 Baroreceptors
in carotid sinuses
and aortic arch
are inhibited.
4a
Sympathetic
impulses to heart
cause HR,
contractility, and
CO.
© 2013 Pearson Education, Inc.
3 Impulses from baroreceptors
activate cardioacceleratory center
(and inhibit cardioinhibitory center)
and stimulate vasomotor center.
Slide 1
Short-term Mechanisms: Chemoreceptor
Reflexes
• Chemoreceptors in aortic arch and large
arteries of neck detect increase in CO2, or
drop in pH or O2
• Cause increased blood pressure by
– Signaling cardioacceleratory center 
increase CO
– Signaling vasomotor center  increase
vasoconstriction
© 2013 Pearson Education, Inc.
Short-term Mechanisms: Influence of Higher
Brain Centers
• Reflexes in medulla
• Hypothalamus and cerebral cortex can
modify arterial pressure via relays to
medulla
• Hypothalamus increases blood pressure
during stress
• Hypothalamus mediates redistribution of
blood flow during exercise and changes in
body temperature
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Short-term Mechanisms: Hormonal Controls
• Short term regulation via changes in
peripheral resistance
• Long term regulation via changes in blood
volume
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Short-term Mechanisms: Hormonal Controls
• Cause increased blood pressure
– Epinephrine and norepinephrine from adrenal
gland  increased CO and vasoconstriction
– Angiotensin II stimulates vasoconstriction
– High ADH levels cause vasoconstriction
• Cause lowered blood pressure
– Atrial natriuretic peptide causes decreased
blood volume by antagonizing aldosterone
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Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism
Arterial pressure
Indirect renal mechanism (renin-angiotensin-aldosterone)
Initial stimulus
Arterial pressure
Physiological response
Result
Inhibits baroreceptors
Sympathetic nervous
system activity
Filtration by kidneys
Angiotensinogen
Renin release
from kidneys
Angiotensin I
Angiotensin converting
enzyme (ACE)
Angiotensin II
Urine formation
Adrenal cortex
ADH release by
posterior pituitary
Thirst via
hypothalamus
Secretes
Aldosterone
Blood volume
Sodium reabsorption
by kidneys
Water reabsorption
by kidneys
Water intake
Blood volume
Mean arterial pressure
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Mean arterial pressure
Vasoconstriction;
peripheral resistance
Long-term Mechanisms: Renal Regulation
•
•
•
Baroreceptors quickly adapt to chronic
high or low BP so are ineffective
Long-term mechanisms control BP by
altering blood volume via kidneys
Kidneys regulate arterial blood pressure
1. Direct renal mechanism
2. Indirect renal (renin-angiotensin-aldosterone)
mechanism
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Direct Renal Mechanism
• Alters blood volume independently of
hormones
– Increased BP or blood volume causes
elimination of more urine, thus reducing BP
– Decreased BP or blood volume causes
kidneys to conserve water, and BP rises
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Indirect Mechanism
• The renin-angiotensin-aldosterone
mechanism
–  Arterial blood pressure  release of renin
– Renin catalyzes conversion of
angiotensinogen from liver to angiotensin I
– Angiotensin converting enzyme, especially
from lungs, converts angiotensin I to
angiotensin II
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Functions of Angiotensin II
• Increases blood volume
– Stimulates aldosterone secretion
– Causes ADH release
– Triggers hypothalamic thirst center
• Causes vasoconstriction directly
increasing blood pressure
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Figure 19.10 Direct and indirect (hormonal) mechanisms for renal control of blood pressure.
Direct renal mechanism
Arterial pressure
Indirect renal mechanism (renin-angiotensin-aldosterone)
Initial stimulus
Arterial pressure
Physiological response
Result
Inhibits baroreceptors
Sympathetic nervous
system activity
Filtration by kidneys
Angiotensinogen
Renin release
from kidneys
Angiotensin I
Angiotensin converting
enzyme (ACE)
Angiotensin II
Urine formation
Adrenal cortex
ADH release by
posterior pituitary
Thirst via
hypothalamus
Secretes
Aldosterone
Blood volume
Sodium reabsorption
by kidneys
Water reabsorption
by kidneys
Water intake
Blood volume
Mean arterial pressure
© 2013 Pearson Education, Inc.
Mean arterial pressure
Vasoconstriction;
peripheral resistance
Figure 19.11 Factors that increase MAP.
Activity of
muscular
pump and
respiratory
pump
Release
of ANP
Fluid loss from
hemorrhage,
excessive
sweating
Crisis stressors:
exercise, trauma,
body
temperature
Conservation
of Na+ and
water by kidneys
Blood volume
Blood pressure
Blood pH
O2
CO2
Blood
volume
Baroreceptors
Chemoreceptors
Venous
return
Activation of vasomotor and cardioacceleratory centers in brain stem
Stroke
volume
Heart
rate
Vasomotor tone;
bloodborne
chemicals
(epinephrine,
NE, ADH,
angiotensin II)
Diameter of
blood vessels
Cardiac output
Physiological response
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Blood
viscosity
Body size
Blood vessel
length
Peripheral resistance
Initial stimulus
Result
Dehydration,
high hematocrit
Mean arterial pressure (MAP)
Monitoring Circulatory Efficiency
• Vital signs: pulse and blood pressure,
along with respiratory rate and body
temperature
• Pulse: pressure wave caused by
expansion and recoil of arteries
• Radial pulse (taken at the wrist) routinely
used
• Pressure points where arteries close to
body surface
– Can be compressed to stop blood flow
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Figure 19.12 Body sites where the pulse is most easily palpated.
Superficial temporal artery
Facial artery
Common carotid artery
Brachial artery
Radial artery
Femoral artery
Popliteal artery
Posterior tibial
artery
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Dorsalis pedis
artery
Measuring Blood Pressure
• Systemic arterial BP
– Measured indirectly by auscultatory method
using a sphygmomanometer
– Pressure increased in cuff until it exceeds
systolic pressure in brachial artery
– Pressure released slowly and examiner
listens for sounds of Korotkoff with a
stethoscope
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Measuring Blood Pressure
• Systolic pressure, normally less than 120
mm Hg, is pressure when sounds first
occur as blood starts to spurt through
artery
• Diastolic pressure, normally less than 80
mm Hg, is pressure when sounds
disappear because artery no longer
constricted; blood flowing freely
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Variations in Blood Pressure
• Transient elevations occur during changes
in posture, physical exertion, emotional
upset, fever.
• Age, sex, weight, race, mood, and posture
may cause BP to vary
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Alterations in Blood Pressure
• Hypertension: high blood pressure
– Sustained elevated arterial pressure of 140/90
or higher
– Prehypertension if values elevated but not
yet in hypertension range
• May be transient adaptations during fever, physical
exertion, and emotional upset
• Often persistent in obese people
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Homeostatic Imbalance: Hypertension
• Prolonged hypertension major cause of
heart failure, vascular disease, renal
failure, and stroke
– Heart must work harder  myocardium
enlarges, weakens, becomes flabby
– Also accelerates atherosclerosis
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Primary or Essential Hypertension
• 90% of hypertensive conditions
• No underlying cause identified
– Risk factors include heredity, diet, obesity,
age, diabetes mellitus, stress, and smoking
• No cure but can be controlled
– Restrict salt, fat, cholesterol intake
– Increase exercise, lose weight, stop smoking
– Antihypertensive drugs
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Homeostatic Imbalance: Hypertension
• Secondary hypertension less common
– Due to identifiable disorders including
obstructed renal arteries, kidney disease, and
endocrine disorders such as hyperthyroidism
and Cushing's syndrome
– Treatment focuses on correcting underlying
cause
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Alterations in Blood Pressure
• Hypotension: low blood pressure
– Blood pressure below 90/60 mm Hg
– Usually not a concern
• Only if leads to inadequate blood flow to tissues
– Often associated with long life and lack of
cardiovascular illness
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Homeostatic Imbalance: Hypotension
• Orthostatic hypotension: temporary low
BP and dizziness when suddenly rising
from sitting or reclining position
• Chronic hypotension: hint of poor
nutrition and warning sign for Addison's
disease or hypothyroidism
• Acute hypotension: important sign of
circulatory shock; threat for surgical
patients and those in ICU
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Circulatory Shock
• Hypovolemic shock: results from largescale blood loss
• Vascular shock: results from extreme
vasodilation and decreased peripheral
resistance
• Cardiogenic shock results when an
inefficient heart cannot sustain adequate
circulation
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Figure 19.18 Events and signs of hypovolemic shock.
Acute bleeding (or other events that reduce
blood volume) leads to:
1. Inadequate tissue perfusion
resulting in O2 and nutrients to cells
Initial stimulus
Physiological response
Signs and symptoms
Result
2. Anaerobic metabolism by cells, so lactic
acid accumulates
3. Movement of interstitial fluid into blood,
so tissues dehydrate
Chemoreceptors activated
(by in blood pH)
Baroreceptor firing reduced
(by blood volume and pressure)
Hypothalamus activated
(by blood pressure)
Brain
Minor effect
Major effect
Respiratory centers
activated
Cardioacceleratory and
vasomotor centers activated
Heart rate
Sympathetic nervous
system activated
ADH
released
Neurons
depressed
by pH
Intense vasoconstriction
(only heart and brain spared)
Central
nervous system
depressed
Kidneys
Renal blood flow
Adrenal
cortex
Renin released
Angiotensin II
produced in blood
Aldosterone
released
Rate and
depth of
breathing
CO2 blown
off; blood
pH rises
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Tachycardia;
weak, thready
pulse
Kidneys retain
salt and water
Skin becomes
cold, clammy,
and cyanotic
Blood pressure maintained;
if fluid volume continues to
decrease, BP ultimately
drops. BP is a late sign.
Water
retention
Urine output
Thirst
Restlessness
(early sign)
Coma
(late sign)
Figure 19.15 Intrinsic and extrinsic control of arteriolar smooth muscle in the systemic circulation.
Vasodilators
Metabolic
O2
CO2
H+
K+
• Prostaglandins
• Adenosine
• Nitric oxide
Neuronal
Sympathetic tone
Hormonal
• Atrial natriuretic
peptide
Extrinsic mechanisms
Intrinsic mechanisms
(autoregulation)
Vasoconstrictors
• Metabolic or myogenic controls
• Distribute blood flow to individual
organs and tissues as needed
Myogenic
• Stretch
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Neuronal
Sympathetic tone
Metabolic
Hormonal
• Endothelins
• Angiotensin II
• Antidiuretic hormone
• Epinephrine
• Norepinephrine
• Neuronal or hormonal controls
• Maintain mean arterial pressure
(MAP)
• Redistribute blood during exercise
and thermoregulation
Hydrostatic Pressures
• Capillary hydrostatic pressure (HPc)
(capillary blood pressure)
– Tends to force fluids through capillary walls
– Greater at arterial end (35 mm Hg) of bed
than at venule end (17 mm Hg)
• Interstitial fluid hydrostatic pressure
(HPif)
– Pressure that would push fluid into vessel
– Usually assumed to be zero because of
lymphatic vessels
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Colloid Osmotic Pressures
• Capillary colloid osmotic pressure
(oncotic pressure) (OPc)
– Created by nondiffusible plasma proteins,
which draw water toward themselves
– ~26 mm Hg
• Interstitial fluid osmotic pressure (OPif)
– Low (~1 mm Hg) due to low protein content
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Hydrostatic-osmotic Pressure Interactions:
Net Filtration Pressure (NFP)
• NFP—comprises all forces acting on
capillary bed
– NFP = (HPc + OPif) – (HPif + OPc)
• Net fluid flow out at arterial end
• Net fluid flow in at venous end
• More leaves than is returned
– Excess fluid returned to blood via lymphatic
system
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Capillary Exchange of Respiratory Gases
and Nutrients
• Diffusion down concentration gradients
– O2 and nutrients from blood to tissues
– CO2 and metabolic wastes from tissues to blood
• Lipid-soluble molecules diffuse directly through
endothelial membranes
• Water-soluble solutes pass through clefts and
fenestrations
• Larger molecules, such as proteins, are actively
transported in pinocytotic vesicles or caveolae
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Figure 19.21b Major arteries of the systemic circulation.
Arteries of the head and trunk
Internal carotid artery
External carotid artery
Common carotid arteries
Vertebral artery
Subclavian artery
Brachiocephalic trunk
Arteries that supply the upper limb
Subclavian artery
Axillary artery
Brachial artery
Aortic arch
Ascending aorta
Coronary artery
Celiac trunk
Abdominal aorta
Superior mesenteric
artery
Renal artery
Gonadal artery
Radial artery
Ulnar artery
Deep palmar arch
Superficial palmar arch
Digital arteries
Arteries that supply the lower
limb
External iliac artery
Inferior mesenteric artery
Femoral artery
Common iliac artery
Popliteal artery
Internal iliac artery
Anterior tibial artery
Posterior tibial artery
Illustration, anterior view
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Arcuate artery
Figure 19.22b Arteries of the head, neck, and brain.
Ophthalmic artery
Basilar artery
Vertebral
artery
Internal
carotid artery
External
carotid artery
Common
carotid artery
Thyrocervical
trunk
Costocervical
trunk
Subclavian
artery
Axillary
artery
Arteries of the head and neck, right aspect
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Branches of
the external
carotid artery
• Superficial
temporal artery
• Maxillary artery
• Occipital artery
• Facial artery
• Lingual artery
• Superior thyroid
artery
Larynx
Thyroid gland
(overlying trachea)
Clavicle (cut)
Brachiocephalic
trunk
Internal thoracic
artery
Figure 19.22d Arteries of the head, neck, and brain.
Anterior
Cerebral arterial
circle
(circle of Willis)
Frontal lobe
Optic chiasma
• Anterior
communicating
artery
Middle
cerebral
artery
• Anterior
cerebral artery
Internal
carotid
artery
• Posterior
communicating
artery
Mammillary
body
• Posterior
cerebral artery
Basilar artery
Temporal
lobe
Vertebral artery
Pons
Occipital lobe
Cerebellum
Posterior
Major arteries serving the brain (inferior view, right side
of cerebellum and part of right temporal lobe removed)
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Figure 19.24b Arteries of the abdomen.
Liver (cut)
Inferior vena cava
Celiac trunk
Common
hepatic artery
Hepatic
artery proper
Gastroduodenal
artery
Right
gastric artery
Diaphragm
Esophagus
Left gastric artery
Stomach
Splenic artery
Left gastroepiploic
artery
Spleen
Gallbladder
Pancreas
(major portion lies
posterior to stomach)
Right gastroepiploic
artery
Duodenum
Abdominal aorta
Superior mesenteric
artery
The celiac trunk and its major branches. The left half of the liver has been removed.
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Figure 19.24c Arteries of the abdomen.
Hiatus (opening)
for inferior vena cava
Hiatus (opening)
for esophagus
Diaphragm
Inferior
phrenic artery
Adrenal
(suprarenal) gland
Middle
suprarenal artery
Celiac trunk
Renal artery
Kidney
Superior
mesenteric artery
Abdominal aorta
Lumbar arteries
Ureter
Median
sacral artery
Major branches of the abdominal aorta.
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Gonadal
(testicular
or ovarian) artery
Inferior
mesenteric artery
Common
iliac artery
Figure 19.24d Arteries of the abdomen.
Celiac trunk
Superior mesenteric
artery
Branches of
the superior
mesenteric artery
• Middle colic artery
• Intestinal arteries
• Right colic artery
• Ileocolic artery
Ascending colon
Right common iliac
artery
Ileum
Transverse colon
Aorta
Inferior mesenteric
artery
Branches of
the inferior
mesenteric artery
• Left colic artery
• Sigmoidal arteries
• Superior rectal
artery
Descending colon
Cecum
Appendix
Distribution of the superior and inferior mesenteric arteries.
The transverse colon has been pulled superiorly.
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Sigmoid colon
Rectum
Figure 19.25b Arteries of the right pelvis and lower limb.
Common iliac artery
Internal iliac artery
Superior gluteal artery
External iliac artery
Deep artery of thigh
Lateral circumflex
femoral artery
Medial circumflex
femoral artery
Obturator artery
Femoral artery
Adductor hiatus
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Fibular artery
Dorsalis pedis artery
Arcuate artery
Dorsal metatarsal
arteries
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Anterior view
Figure 19.25c Arteries of the right pelvis and lower limb.
Popliteal artery
Anterior tibial
artery
Posterior tibial
artery
Lateral plantar
artery
Medial plantar
artery
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Posterior view
Fibular artery
Dorsalis pedis
artery (from top
of foot)
Plantar arch
Figure 19.26b Major veins of the systemic circulation.
Veins of the head and trunk
Dural venous sinuses
External jugular vein
Vertebral vein
Internal jugular vein
Right and left
brachiocephalic veins
Superior vena cava
Great cardiac vein
Hepatic veins
Splenic vein
Hepatic portal vein
Renal vein
Superior mesenteric vein
Inferior mesenteric vein
Inferior vena cava
Common iliac vein
Internal iliac vein
Veins that drain
the upper limb
Subclavian vein
Axillary vein
Cephalic vein
Brachial vein
Basilic vein
Median cubital vein
Ulnar vein
Radial vein
Digital veins
Veins that drain
the lower limb
External iliac vein
Femoral vein
Great saphenous vein
Popliteal vein
Posterior tibial vein
Anterior tibial vein
Small saphenous vein
Dorsal venous arch
Dorsal metatarsal veins
Illustration, anterior view. The vessels of the pulmonary circulation are not shown.
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Figure 19.27b Venous drainage of the head, neck, and brain.
Ophthalmic vein
Superficial
temporal vein
Facial vein
Occipital vein
Posterior
auricular vein
External
jugular vein
Vertebral vein
Internal
jugular vein
Superior and
middle thyroid veins
Brachiocephalic
vein
Subclavian vein
Superior
vena cava
Veins of the head and neck, right superficial aspect
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Figure 19.27c Venous drainage of the head, neck, and brain.
Superior sagittal sinus
Falx cerebri
Inferior sagittal sinus
Straight sinus
Cavernous sinus
Transverse sinuses
Sigmoid sinus
Jugular foramen
Right internal jugular vein
Dural venous sinuses of the brain
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Figure 19.28b Veins of the thorax and right upper limb.
Brachiocephalic veins
Right subclavian vein
Axillary vein
Brachial vein
Cephalic vein
Basilic vein
Internal jugular vein
External jugular vein
Left subclavian vein
Superior vena cava
Azygos vein
Accessory hemiazygos
vein
Hemiazygos vein
Posterior intercostals
Inferior vena cava
Ascending lumbar vein
Median cubital
vein
Median
antebrachial vein
Cephalic vein
Radial vein
Anterior view
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Basilic vein
Ulnar vein
Deep venous
palmar arch
Superficial venous
palmar arch
Digital veins
Figure 19.29a Veins of the abdomen.
Inferior vena cava
Cystic vein
Hepatic
portal
system
Inferior phrenic veins
Hepatic veins
Hepatic portal vein
Superior mesenteric vein
Splenic vein
Suprarenal veins
Renal veins
Inferior
mesenteric
vein
Gonadal veins
Lumbar veins
R. ascending
lumbar vein
L. ascending
lumbar vein
Common iliac veins
External iliac vein
Internal iliac veins
Schematic flowchart.
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Figure 19.29b Veins of the abdomen.
Hepatic veins
Inferior phrenic
vein
Inferior vena cava
Right suprarenal
vein
Left suprarenal
vein
Renal veins
Right gonadal
vein
External iliac
vein
Left ascending
lumbar vein
Lumbar veins
Left gonadal
vein
Common iliac
vein
Internal iliac
vein
Tributaries of the inferior vena cava.
Venous drainage of abdominal organs not drained by the hepatic portal vein.
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Figure 19.29c Veins of the abdomen.
Hepatic veins
Liver
Hepatic portal
vein
Gastric veins
Spleen
Inferior vena cava
Splenic vein
Right
gastroepiploic vein
Inferior
mesenteric vein
Superior
mesenteric vein
Small intestine
Large intestine
Rectum
The hepatic portal circulation.
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Figure 19.30b Veins of the right lower limb.
Common iliac vein
Internal iliac vein
External iliac vein
Inguinal ligament
Femoral vein
Great saphenous
vein (superficial)
Popliteal vein
Small
saphenous vein
Fibular vein
Anterior
tibial vein
Dorsalis
pedis vein
Dorsal
venous arch
Dorsal
metatarsal veins
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Anterior view