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Blood Vessels

Blood is carried in a closed system of vessels that begins and
ends at the heart

In adult, blood vessels stretch 60,000 miles!

The three major types of vessels are arteries, capillaries, and
veins

Arteries carry blood away from the heart (O2 rich, except
pulmonary)


Veins carry blood toward the heart (O2 poor, except pulmonary)


They branch, diverge, fork
They join, merge, converge
Capillaries contact tissue cells and directly serve cellular needs
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Generalized Structure of Blood Vessels



Arteries and veins are composed of three tunics –
tunica interna, tunica media, and tunica externa
Lumen – central blood-containing space
surrounded by tunics
Capillaries are composed of endothelium with
sparse basal lamina
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Generalized Structure of Blood Vessels
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Figure 19.1b
Tunics


Tunica interna (tunica intima)

Endothelial layer that lines the lumen of all vessels

Continuation w/ the endocardial lining of the heart

Flat cells, slick surface

In vessels larger than 1 mm, a subendothelial connective
tissue basement membrane is present
Tunica media

Circularly arranged smooth muscle and elastic fiber layer,
regulated by sympathetic nervous system

Controls vasoconstriction/vasodilation of vessels
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Tunics

Tunica externa (tunica adventitia)

Collagen fibers that protect and reinforce vessels

Contains nerve fibers, lymphatic vessels, & elastin
fibers

Larger vessels contain vasa vasorum that nourish
more external tissues of the blood vessel wall
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Blood Vessel Anatomy
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Table 19.1
Elastic (Conducting) Arteries

Thick-walled arteries near the heart; the aorta and
its major branches

Large lumen allow low-resistance conduction of
blood

Contain elastin in all three tunics

Inactive in vasoconstriction

Serve as pressure reservoirs expanding and
recoiling as blood is ejected from the heart
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Muscular (Distributing) Arteries and Arterioles



Muscular arteries – distal to elastic arteries; deliver
blood to body organs
Account for most of the named structures in lab

Have thickest tunica media (proportionally) of all
the vessels

Active in vasoconstriction
Arterioles – smallest arteries; lead to capillary beds

Control flow into capillary beds via vasodilation
and constriction
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Capillaries

Capillaries are the smallest blood vessels (microscopic)

Walls consisting of a thin tunica interna, one cell thick

Allow only a single RBC to pass at a time

Pericytes on the outer surface stabilize their walls

Tissues have a rich capillary supply

Tendons, ligaments are poorly vascularized

Cartilage, cornea, lens, and epithelia lack capillaries
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Vascular Components
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Figure 19.2a, b
Types of Capillaries

There are three structural types of capillaries:

Continuous

Fenestrated

Sinusoids
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Continuous Capillaries

Continuous capillaries are abundant in the skin and muscles

Endothelial cells provide an uninterrupted lining

Adjacent cells are connected with tight junctions

Intercellular clefts allow the passage of fluids & small solutes

Brain capillaries do not have clefts (blood-brain barrier)
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Fenestrated Capillaries

Found wherever active capillary absorption or filtrate formation
occurs (e.g., small intestines, endocrine glands, and kidneys)

Characterized by:

An endothelium riddled with pores (fenestrations)

Greater permeability than other capillaries
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Sinusoids

Highly modified, leaky, fenestrated capillaries with large lumens

Found in the liver, bone marrow, lymphoid tissue, and in some endocrine
organs

Allow large molecules (proteins and blood cells) to pass between the blood
and surrounding tissues

Blood flows sluggishly (e.g. in spleen) allowing for removal of unwanted
debris and immunogens
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Capillary Beds

A microcirculation moving from arterioles to venules

Consist of two types of vessels:


Vascular shunts – metarteriole–thoroughfare channel
connecting an arteriole directly with a postcapillary venule
True capillaries – the actual exchange vessels

Terminal arteriole feeds metarteriole which is
continuous w/ the thoroughfare channel which
joins the postcapillary venule
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Blood Flow Through Capillary Beds

True capillaries: 10-100/bed

Branch from, then return to, the capillary bed

Precapillary sphincter


Cuff of smooth muscle that surrounds each true capillary at
the metarteriole and acts as a valve to regulate flow
Blood flow is regulated by vasomotor nerves and local
chemical conditions

True bed is open after meals, closed between meals

True bed is rerouted to skeletal muscles during physical
exercise
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Capillary Beds
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Figure 19.4a
Capillary Beds
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Figure 19.4b
Venous System: Venules



Venules are formed when capillary beds unite
Postcapillary venules – smallest venules,
composed of endothelium and a few pericytes
Allow fluids and WBCs to pass from the
bloodstream to tissues
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Venous System: Veins

Veins:

Formed when venules converge

Composed of three tunics, with a thin tunica media
and a thick tunica externa consisting of collagen
fibers and elastic networks

Accommodate a large blood volume

Capacitance vessels (blood reservoirs) that contain
65% of the blood supply
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Venous System: Veins

Veins have much lower blood pressure and thinner
walls than arteries

To return blood to the heart, veins have special
adaptations


Large-diameter lumens, which offer little resistance
to flow

Valves (resembling semilunar heart valves), which
prevent backflow of blood
Venous sinuses – specialized, flattened veins with
extremely thin walls (e.g., coronary sinus of the
heart and dural sinuses of the brain)
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Vascular Anastomoses

Merging blood vessels, more common in veins than
arteries

Arterial anastomoses provide alternate pathways (collateral
channels) for blood to reach a given body region


If one branch is blocked, the collateral channel can supply
the area with adequate blood supply

E.g. occur around joints, abdominal organs, brain, & heart

E.g. poorly anastomized organs are retina, kidney, spleen
Thoroughfare channels are examples of arteriovenous
anastomoses
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Physiology of Circulation: Blood Flow

Actual volume of blood flowing in a given period:

Is measured in ml per min.

Is equivalent to cardiac output (CO), considering
the entire vascular system

Is relatively constant when at rest

Varies widely through individual organs
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Blood Pressure (BP)


Force / unit area exerted on the wall of a blood
vessel by its contained blood

Expressed in millimeters of mercury (mm Hg)

Measured in reference to systemic arterial BP in
large arteries near the heart
The differences in BP within the vascular system
provide the driving force that keeps blood moving
from higher to lower pressure areas
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Resistance

Resistance – opposition to flow (friction)

Measure of the amount of friction blood encounters

Generally encountered in the systemic circulation away
from the heart


Referred to as peripheral resistance (PR)
The three sources of resistance are:

Blood viscosity

Total blood vessel length

Blood vessel diameter
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Resistance Factors: Viscosity and Vessel
Length

Resistance factors that remain relatively constant are:


Blood viscosity:

Internal resistance to flow that exist in all fluids

Increased viscosity increases resistance (molecules
ability to slide past one another)
Blood vessel length:

The longer the vessel, the greater the resistance

E.g. one extra pound of fat = 1 mile of small vessels
required to service it = more resistance
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Resistance Factors: Blood Vessel Diameter

Changes in vessel diameter are frequent and significantly
alter peripheral resistance
Fluid flows slowly
Fluid flows freely

The smaller the tube the greater the resistance

Resistance varies inversely with the fourth power of vessel
radius

For example, if the radius is doubled, the resistance is 1/16
as much
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Resistance Factors: Blood Vessel Diameter

Small-diameter arterioles are the major
determinants of peripheral resistance

Fatty plaques from atherosclerosis:

Cause turbulent blood flow

Dramatically increase resistance due to turbulence
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Blood Flow, Blood Pressure, and Resistance

Blood flow (F) is directly proportional to the difference in
blood pressure (P) between two points in the circulation


Blood flow is inversely proportional to resistance (R)


If P increases, blood flow speeds up; if P decreases,
blood flow declines
If R increases, blood flow decreases
R is more important than P in influencing local blood
pressure
F = P/R
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Systemic Blood Pressure

Any fluid driven by a pump thru a circuit of closed
channels operates under pressure

The fluid closest to the pump is under the greatest
pressure

The heart generates blood flow.

Pressure results when flow is opposed by
resistance…eg. Systemic Blood Pressure
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Systemic Blood Pressure


Systemic pressure:

Is highest in the aorta

Declines throughout the length of the pathway

Is 0 mm Hg in the right atrium
The steepest change in blood pressure occurs in the
arterioles which offer the greatest resistance to
blood flow
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Systemic Blood Pressure
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Figure 19.5
Arterial Blood Pressure


Arterial BP reflects two factors of the arteries close
to the heart

Their elasticity (how much they can be stretched)

The volume of blood forced into them at any given
time
Blood pressure in elastic arteries near the heart is
pulsatile (BP rises and falls)
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Arterial Blood Pressure


Systolic pressure – pressure exerted on arterial
walls during left ventricular contraction pushing
blood into the aorta (120 mm Hg)
Diastolic pressure – aortic SL valve closes
preventing backflow and the walls of the aorta
recoil resulting in pressure drop

lowest level of arterial pressure during a
ventricular cycle
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Arterial Blood Pressure

Pulse pressure – the difference between systolic and diastolic pressure



Felt as a pulse during systole as arteries are expanded
Mean arterial pressure (MAP) – pressure that propels the blood to the
tissues
Because diastole is longer than systole…

MAP = diastolic pressure + 1/3 pulse pressure

E.g. systolic BP = 120 mm Hg

E.g. diastolic BP = 80 mm Hg

MAP = 93

MAP & pulse pressure decline w/ distance from the heart

At the arterioles blood flow is steady
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Capillary Blood Pressure

Capillary BP ranges from 40 (beginning) to 20
(end) mm Hg

Low capillary pressure is desirable because high
BP would rupture fragile, thin-walled capillaries

Low BP is sufficient to force filtrate out into
interstitial space and distribute nutrients, gases,
and hormones between blood and tissues
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Venous Blood Pressure

Venous BP is steady and changes little during the
cardiac cycle

The pressure gradient in the venous system is only
about 20 mm Hg (from venules to venae cavae) vs.
60 mm Hg from the aorta to the arterioles

A cut vein has even blood flow; a lacerated artery
flows in spurts
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Factors Aiding Venous Return

Venous BP alone is too low to promote adequate
blood return and is aided by the:



Respiratory “pump” – pressure changes created
during breathing suck blood toward the heart by
squeezing local veins
Muscular “pump” – contraction of skeletal muscles
surrounding deep veins “pump” blood toward the
heart with valves prevent backflow during venous
return
Smooth muscle contraction of the tunica media by
the SNS
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Factors Aiding Venous Return
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Figure 19.6
Maintaining Blood Pressure

Maintaining blood pressure requires:

Cooperation of the heart, blood vessels, and
kidneys

Supervision of the brain
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Maintaining Blood Pressure

The main factors influencing blood pressure are:

Cardiac output (CO)

Peripheral resistance (PR)

Blood volume

Blood pressure = CO x PR

Blood pressure varies directly with CO, PR, and
blood volume

Changes in one (CO, PR, BV) are compensated by
the others to maintain BP
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Cardiac Output (CO)

CO = stroke volume (ml/beat) x heart rate (beats/min)

Units are L/min

Cardiac output is determined by venous return and neural
and hormonal controls

Resting heart rate is controlled by the cardioinhibitory
center via the vagus nerves

Stroke volume is controlled by venous return (end diastolic
volume, or EDV)

Under stress, the cardioacceleratory center increases heart
rate and stroke volume

The end systolic volume (ESV) decreases and MAP
increases
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Cardiac Output (CO)
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Figure 19.7
Controls of Blood Pressure


Short-term controls:

Are mediated by the nervous system and
bloodborne chemicals

Counteract moment-to-moment fluctuations in
blood pressure by altering peripheral resistance
Long-term controls regulate blood volume
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Short-Term Mechanisms: Neural Controls


Neural controls of peripheral resistance:

Alter blood distribution in response to demands

Maintain MAP by altering blood vessel diameter
Neural controls operate via reflex arcs involving:

Baroreceptors & afferent fibers

Vasomotor centers of the medulla

Vasomotor fibers

Vascular smooth muscle
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Short-Term Mechanisms: Vasomotor Center

Vasomotor center – a cluster of sympathetic neurons in the
medulla that oversees changes in blood vessel diameter


Maintains blood vessel tone by innervating smooth muscles
of blood vessels, especially arterioles
Cardiovascular center – vasomotor center plus the cardiac
centers that integrate blood pressure control by altering
cardiac output and blood vessel diameter

Vasomotor fibers (T1-L2) innervate smooth muscle of the
arterioles

Vasomotor state is always in a state of moderate
constriction
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Short-Term Mechanisms: Vasomotor Activity


Sympathetic activity causes:

Vasoconstriction and a rise in BP if increased

BP to decline to basal levels if decreased
Vasomotor activity is modified by:

Baroreceptors (pressure-sensitive), chemoreceptors
(O2, CO2, and H+ sensitive), higher brain centers,
bloodborne chemicals, and hormones
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Short-Term Mechanisms: BaroreceptorInitiated Reflexes

When arterial blood pressure rises, it stretches
baroreceptos located in the carotid sinuses, aortic arch,
walls of most large arteries of the neck & thorax

Baroreceptors send impulses to the vasomotor center
inhibiting it resulting in vasodilation of arterioles and veins
and decreasing blood pressure

Venous dilation shifts blood to venous reservoirs causing a
decline in venous return and cardiac output

Baroreceptors stimulate parasympathetic activity and
inhibit the cardioacceletory center to decrease heart rate
and contractile force
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Short-Term Mechanisms: BaroreceptorInitiated Reflexes
 Declining blood pressure stimulates the
cardioacceleratory center to:

Increase cardiac output and vasoconstriction
causing BP to rise

Peripheral resistance & cardiac output are
regulated together to minimize changes in BP
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Short-Term Mechanisms: Baroreceptor-Initiated
Reflexes

Baroreceptors respond to rapidly changing
conditions like when you change posture

They are ineffective against sustained pressure
changes, e.g. chronic hypertension, where they will
adapt and raise their set-point
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Impulse traveling along
afferent nerves from
baroreceptors:
Stimulate cardioinhibitory center
(and inhibit cardioacceleratory center)
Baroreceptors
in carotid
sinuses and
aortic arch
stimulated
Sympathetic
impulses to
heart
( HR and contractility)
CO
Inhibit
vasomotor center
R
Rate of vasomotor
impulses allows
vasodilation
( vessel diameter)
Arterial
blood pressure
rises above
normal range
CO and R
return blood
pressure to
Homeostatic
range
Stimulus:
Rising blood
pressure
Homeostasis: Blood pressure in normal range
Stimulus:
Declining
blood pressure
CO and R
return blood
pressure to
homeostatic
range
Peripheral
resistance (R)
Cardiac
output
(CO)
Impulses from
baroreceptors:
Stimulate cardioacceleratory center
(and inhibit cardioinhibitory center)
Sympathetic
impulses to heart
( HR and contractility)
Vasomotor
fibers
stimulate
vasoconstriction
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Arterial blood pressure
falls below normal range
Baroreceptors in
carotid sinuses
and aortic arch
inhibited
Stimulate
vasomotor
center
Figure 19.8
Short-Term Mechanisms: Chemical Controls

Blood pressure is regulated by chemoreceptor
reflexes sensitive to oxygen and carbon dioxide

Prominent chemoreceptors are found in the carotid
and aortic bodies

Response is to increase cardiac output and
vasoconstriction

Increased BP speeds the return of blood to the heart
and lungs
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Influence of Higher Brain Centers

Reflexes that regulate BP are integrated in the
medulla

Higher brain centers (cortex and hypothalamus)
can modify BP via relays to medullary centers
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Chemicals that Increase Blood Pressure


Adrenal medulla hormones – norepinephrine and
epinephrine increase blood pressure

NE has a vasoconstrictive action

E increases cardiac output and causes
vasodilation in skeletal muscles
Nicotine causes vasoconstriction: stimulates
sympathetic neurons and the release of large
amounts of NE & E
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Chemicals that Increase Blood Pressure


Antidiuretic hormone (ADH, aka vasopressin) –
produced by the hypothalamus and causes intense
vasoconstriction in cases of extremely low BP. It
also stimulates the kidneys to conserve H2O
Angiotensin II – released when renal perfusion is
inadequate. The kidney’s release of renin
generates angiotensin II, which causes
vasoconstriction
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Chemicals that Decrease Blood Pressure




Atrial natriuretic peptide (ANP) – produced by the
atrium and causes blood volume and pressure to
decline along with general vasodilation
Nitric oxide (NO) – is a brief but potent
vasodilator
Inflammatory chemicals – histamine, prostacyclin,
and kinins are potent vasodilators
Alcohol – causes BP to drop by inhibiting ADH
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Long-Term Mechanisms: Renal Regulation

Long-term mechanisms control BP by altering
blood volume

Baroreceptors adapt to chronic high or low BP

Increased BP stimulates the kidneys to eliminate
water, thus reducing BP

Decreased BP stimulates the kidneys to increase
blood volume and BP
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Kidney Action and Blood Pressure

Kidneys act directly and indirectly to maintain
long-term blood pressure

Direct renal mechanism alters blood volume

Indirect renal mechanism involves the reninangiotensin mechanism
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Kidney Action and Blood Pressure: Direct Renal
Mechanism

Increase in BV causes an increase in BP

This stimulates the kidneys to release H2O which
lowers BV which in turn lowers BP
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Kidney Action and Blood Pressure: Indirect Renal
Mechanism

Declining BP causes the release of renin, which
triggers the release of angiotensin II

Angiotensin II is a potent vasoconstrictor that
stimulates aldosterone secretion

Aldosterone enhances renal reabsorption resulting
in increased BP and BP
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Kidney Action and Blood Pressure
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Figure 19.9
Monitoring Circulatory Efficiency



Efficiency of the circulation can be assessed by
taking pulse and blood pressure measurements
Vital signs – pulse and blood pressure, along with
respiratory rate and body temperature
Pulse – pressure wave caused by the expansion and
recoil of elastic arteries

Radial pulse (taken on the radial artery at the wrist)
is routinely used
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Palpated Pulse
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Figure 19.11
Measuring Blood Pressure

Systemic arterial BP is measured indirectly with
the auscultatory method

A sphygmomanometer is placed on the arm
superior to the elbow

Pressure is increased in the cuff until it is greater
than systolic pressure in the brachial artery

Pressure is released slowly and the examiner
listens with a stethoscope
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Measuring Blood Pressure

The first sound heard is recorded as the systolic
pressure

The pressure when sound disappears is recorded as
the diastolic pressure
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Alterations in Blood Pressure



Normal BP at rest: 110-140 mm Hg (systolic) &
70-80 mm Hg (diastolic)
Hypotension – low BP in which systolic pressure is
below 100 mm Hg
Hypertension – condition of sustained elevated
arterial pressure of 140/90 or higher
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Blood Flow Through Tissues

Blood flow, or tissue perfusion, is involved in:

Delivery of oxygen and nutrients to, and removal
of wastes from, tissue cells

Gas exchange in the lungs

Absorption of nutrients from the digestive tract

Urine formation by the kidneys
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Velocity of Blood Flow

Blood velocity:

Changes as it travels through the systemic
circulation

Is inversely proportional to the cross-sectional area

E.g. Fast in the aorta
Slow in capillaries
Fast again in the veins
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Velocity of Blood Flow
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Figure 19.13
Autoregulation: Local Regulation of Blood
Flow
 Autoregulation – automatic adjustment of blood
flow to each tissue in proportion to its
requirements at any given point in time

Blood flow through an individual organ is
intrinsically controlled by modifying the diameter
of local arterioles feeding its capillaries

MAP remains constant, while local demands
regulate the amount of blood delivered to various
areas according to need
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Blood Flow: Skeletal Muscles

Capillary density & blood flow is greater in red
(slow oxidative) fibers than in white (fast
glycolytic) fibers

When muscles become active, blood flow to them
increases (hyperemia)

This autoregulation occurs in response to low O2
levels

SNS activity increases causing an increase in NE
which causes vasoconstriction of the vessels of
blood reservoirs to the skin and viscera diverting
blood away to the skeletal muscles
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Blood Flow: Brain

Blood flow to the brain is constant, as neurons are intolerant of ischemia

Brain cannot store essential nutrients

Very precise autoregulatory system,



E.g. when you make a fist, blood supply shifts to those neurons
in the cerobral motor cortex
Metabolic controls – brain tissue is extremely sensitive to declines in pH,
and increased carbon dioxide causes marked vasodilation
Myogenic controls protect the brain from damaging changes in blood
pressure

Decreases in MAP cause cerebral vessels to dilate to ensure adequate
perfusion

Increases in MAP cause cerebral vessels to constrict so smaller vessels
do not rupture

MAP below 60mm Hg can cause syncope (fainting)
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Blood Flow: Skin

Blood flow through the skin:

Supplies nutrients to cells in response to oxygen
need

Helps maintain body temperature

Provides a blood reservoir
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Blood Flow: Skin

Blood flow to venous plexuses below the skin
surface:

Varies from 50 ml/min (cold) to 2500 ml/min (hot),
depending on body temperature

Is controlled by sympathetic nervous system
reflexes initiated by temperature receptors and the
central nervous system

Does this via arteriole-venule shunts located at
fingertips, palms, toes, soles of feet, ears, nose, lips
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Temperature Regulation


As temperature rises (e.g., heat exposure, fever, vigorous
exercise):

Hypothalamic signals reduce vasomotor stimulation of the
skin vessels

Blood flushes into capillary beds

Heat radiates from the skin
Sweat also causes vasodilation via bradykinin in perspiration


Bradykinin stimulates the release of NO which increases
vasodilation
As temperature decreases, skin vessels constrict and blood is
shunted to deeper, more vital organs

Rosy cheeks: blood entrapment in superficial
capillary loops
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Blood Flow: Lungs (Think Reversal)

Blood flow in the pulmonary circulation is unusual
in that:

The pathway is short

Arteries/arterioles are more like veins/venules
(thin-walled, with large lumens)

Because of this they have a much lower arterial
pressure (24/8 mm Hg versus 120/80 mm Hg)
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Blood Flow: Lungs

The autoregulatory mechanism is exactly opposite
of that in most tissues

Low pulmonary oxygen levels cause
vasoconstriction; high levels promote
vasodilation

As lung air sacs fill w/ air, capillary beds dilate
to take it up
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Blood Flow: Heart


Small vessel coronary circulation is influenced by:

Aortic pressure

The pumping activity of the ventricles
During ventricular systole:

Coronary vessels compress

Myocardial blood flow ceases

Stored myoglobin supplies sufficient oxygen

During ventricular diastole, aortic pressure forces blood thru the
coronary circulation

During exercise, coronary blood vessels dilate in response to
elevated CO2 levels
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Capillary Exchange of Respiratory Gases and
Nutrients
 Oxygen, carbon dioxide, nutrients, and metabolic
wastes diffuse between the blood and interstitial
fluid along concentration gradients

Oxygen and nutrients pass from the blood to
tissues

Carbon dioxide and metabolic wastes pass from
tissues to the blood

Water-soluble solutes pass through clefts and
fenestrations

Lipid-soluble molecules diffuse directly through
endothelial membranes
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Capillary Exchange of Respiratory Gases and
Nutrients
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Figure 19.15.1
Four Routes Across Capillaries
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Figure 19.15.2
Fluid Movement: Bulk Flow

Fluid is forced out of capillary beds thru clefts at
the arterial end, with most of it returning at the
venous end of the bed

This process determines relative fluid volume in
blood stream and extracellular space
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Capillary Exchange: Fluid Movements

Hydrostatic pressure is the force of a fluid pressed
against a wall

Direction and amount of fluid flow depends upon
the difference between:

Capillary hydrostatic pressure (HPc)

Capillary colloid osmotic pressure (OPc)
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Capillary Exchange: Fluid Movements

HPc – pressure of blood against the capillary walls:

Tends to force fluids through the capillary walls
(filtration) leaving behind cells and proteins

Is greater at the arterial end of a bed than at the
venule end

HPc is opposed by interstitial fluid hydrostatic
pressure (HPif)

Net pressure is the difference between HPc and
HPif
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Colloid Osmotic Pressure


The force opposing hydrostatic pressure (HPc)
OPc– created by nondiffusible plasma proteins,
which draw water toward themselves (osmosis)

E.g. serum albumin

OPc does not vary from one end of the capillary
bed to the other
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Net Filtration Pressure (NFP)



Hydrostatic-Osmotic Pressure interactions
determine if there is a net gain or loss of fluid from
the blood, calculated as the Net Filtration Pressure
(NFP)
NFP – all the forces acting on a capillary bed
Thus, fluid will leave the capillary bed if the NFP
is greater than the net OP and vice versa
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Net Filtration Pressure (NFP)

At the arterial end of a bed, hydrostatic forces
dominate (fluids flow out)

At the venous end of a bed, osmotic forces
dominate (fluids flow in)

More fluids enter the tissue beds than return blood,
and the excess fluid is returned to the blood via the
lymphatic system
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Net Filtration Pressure (NFP)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 19.16
Circulatory Shock


Circulatory shock – any condition in which blood
vessels are inadequately filled and blood cannot
circulate normally
E.g. hypovolemic shock: large scale blood loss

Blood volume decreases causing an increase in
heart rate resulting in a weak pulse

Vasoconstriction occurs enhancing venous
return
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Circulatory Shock

Vascular Shock:

Blood volume is normal, but circulation is poor as a result
of an abnormal expansion of the vascular bed caused by
extreme vasodilation

Results in rapid fall in blood pressure

Most common cause is anaphylactic shock

Body-wide vasodilation due to massive histamine
release

Neurogenic shock: failure of ANS regulation

Septic shock (septicemia): severe systemic bacterial
infection
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
KU Game Day!!

No Games 

But Valentine’s Day is Wednesday 
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 19.17
Circulatory Pathways

The vascular system has two distinct circulations


Pulmonary circulation – short loop that runs from
the heart to the lungs and back to the heart
Systemic circulation – routes blood through a long
loop to all parts of the body and returns to the heart
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Differences Between Arteries and Veins
Arteries
Veins
Delivery
Blood pumped into single
systemic artery – the aorta
Blood returns via superior and
interior venae cavae and the
coronary sinus
Location
Deep, and protected by
tissue
Both deep and superficial
Pathways
Fair, clear, and defined
Convergent interconnections
Supply/drainage
Predictable supply
Dural sinuses and hepatic portal
circulation
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Developmental Aspects

The endothelial lining of blood vessels arises from
mesodermal cells, which collect in blood islands

Blood islands form rudimentary vascular tubes
through which the heart pumps blood by the fourth
week of development

Fetal shunts (foramen ovale and ductus arteriosus)
bypass nonfunctional lungs

The ductus venosus bypasses the liver

The umbilical vein and arteries circulate blood to
and from the placenta
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Developmental Aspects

Blood vessels are trouble-free during youth

Vessel formation occurs:


As needed to support body growth

For wound healing

To rebuild vessels lost during menstrual cycles
With aging, varicose veins, atherosclerosis, and
increased blood pressure may arise
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Pulmonary Circulation
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Figure 19.18b
Systemic Circulation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 19.19
Internal carotid artery
External carotid artery
Vertebral artery
Brachiocephalic trunk
Axillary artery
Ascending aorta
Brachial artery
Abdominal aorta
Superior mesenteric artery
Gonadal artery
Inferior mesenteric
artery
Common iliac artery
External iliac artery
Digital arteries
Femoral artery
Common carotid arteries
Subclavian artery
Aortic arch
Coronary artery
Thoracic aorta
Branches of celiac trunk:
• Left gastric artery
• Splenic artery
• Common hepatic artery
Renal artery
Radial artery
Ulnar artery
Internal iliac artery
Deep palmar arch
Superficial palmar arch
Popliteal artery
Anterior tibial artery
Posterior tibial artery
Arcuate artery
(b)
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Figure 19.20b
Superficial
temporal artery
Basilar artery
Occipital artery
Vertebral artery
Internal
carotid artery
External
carotid artery
Common
carotid artery
Thyrocervical
trunk
Costocervical
trunk
Subclavian
artery
Axillary
artery
(b)
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Ophthalmic artery
Maxillary artery
Facial artery
Lingual artery
Superior thyroid
artery
Larynx
Thyroid gland
(overlying trachea)
Clavicle (cut)
Brachiocephalic
trunk
Internal thoracic
artery
Figure 19.21b
Arteries of the Brain
Anterior
Frontal lobe
Optic chiasma
Middle
cerebral
artery
Internal
carotid
artery
Pituitary
gland
Cerebral arterial
circle
(circle of Willis)
• Anterior
communicating
artery
• Anterior
cerebral artery
• Posterior
communicating
artery
• Posterior
cerebral artery
Basilar artery
Temporal
lobe
Pons
Occipital
lobe
Vertebral artery
Cerebellum
(c)
(d)
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Posterior
Figure 19.21c,d
Common carotid
arteries
Right subclavian
artery
Left subclavian
artery
Left axillary
artery
Brachiocephalic
trunk
Vertebral artery
Thyrocervical trunk
Costocervical trunk
Suprascapular artery
Thoracoacromial artery
Axillary artery
Subscapular artery
Posterior circumflex
humeral artery
Anterior circumflex
humeral artery
Brachial artery
Posterior
intercostal
arteries
Anterior
intercostal
artery
Internal
thoracic
artery
Descending
aorta
Lateral
thoracic
artery
Deep artery
of arm
Common
interosseous
artery
Radial
artery
Ulnar
artery
Deep palmar arch
Superficial palmar arch
Digitals
(b)
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Figure 19.22b
Arteries of the Abdomen
Liver (cut)
Inferior vena cava
Celiac trunk
Hepatic artery
proper
Common hepatic
artery
Right gastric artery
Gallbladder
Gastroduodenal
artery
Right gastroepiploic
artery
Duodenum
Abdominal aorta
(b)
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Diaphragm
Esophagus
Left gastric
artery
Left gastroepiploic
artery
Splenic artery
Spleen
Stomach
Pancreas
(major portion
lies posterior
to stomach)
Superior
mesenteric
artery
Figure 19.23b
Arteries of the Abdomen
Opening
for inferior
vena cava
Hiatus (opening)
for esophagus
Celiac trunk
Diaphragm
Inferior phrenic
artery
Middle suprarenal
artery
Renal artery
Kidney
Superior
mesenteric artery
Lumbar arteries
Abdominal aorta
Median sacral
artery
Gonadal (testicular
or ovarian) artery
Inferior
mesenteric artery
Common iliac artery
Ureter
(c)
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Figure 19.23c
Arteries of the Abdomen
Celiac trunk
Middle colic artery
Right colic artery
Ileocolic artery
Ascending colon
Ileum
Superior rectal
artery
Cecum
Appendix
Transverse colon
Superior
mesenteric artery
Intestinal arteries
Left colic artery
Inferior
mesenteric artery
Aorta
Sigmoidal arteries
Descending colon
Left common
iliac artery
Sigmoid colon
Rectum
(d)
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Figure 19.23d
Arteries of the
Lower Limbs
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
Popliteal
artery
Posterior
tibial
artery
Lateral
plantar
artery
Medial
plantar
artery
Anterior
tibial
artery
Fibular
artery
Dorsalis
pedis artery
(from top
of foot)
Plantar
arch
(c)
Dorsalis pedis artery
Arcuate artery
Metatarsal arteries
(b)
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Figure 19.24b, c
Dural sinuses
External jugular vein
Vertebral vein
Internal jugular vein
Superior vena cava
Axillary vein
Great cardiac vein
Hepatic veins
Hepatic portal vein
Superior mesenteric
vein
Inferior vena cava
Ulnar vein
Radial vein
Digital veins
Common iliac vein
External iliac vein
Femoral vein
Great saphenous vein
Popliteal vein
Posterior tibial vein
Anterior tibial vein
Fibular vein
Dorsal venous arch
(b)
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Subclavian vein
Right and left
brachiocephalic veins
Cephalic vein
Brachial vein
Basilic vein
Splenic vein
Median cubital vein
Renal vein
Inferior mesenteric vein
Internal iliac vein
Dorsal digital
veins
Figure 19.25b
Veins of the Head and Neck
Ophthalmic vein
Superficial
temporal vein
Facial vein
Occipital vein
(b)
Posterior
auricular vein
External
jugular vein
Vertebral vein
Internal
jugular vein
Superior and middle
thyroid veins
Brachiocephalic
vein
Subclavian
vein
Superior
vena cava
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Figure 19.26b
Veins of the Brain
Superior sagittal
sinus
Falx cerebri
Inferior sagittal
sinus
Straight sinus
Cavernous sinus
Junction of sinuses
Transverse sinuses
Sigmoid sinus
Jugular foramen
(c)
Right internal
jugular vein
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Figure 19.26c
Veins of the Upper Limbs and Thorax
Internal jugular vein
External jugular vein
Brachiocephalic veins
Left subclavian vein
Right subclavian vein
Superior vena cava
Axillary vein
Azygos vein
Accessory hemiazygos vein
Brachial vein
Cephalic vein
Basilic vein
Hemiazygos vein
Posterior
intercostals
Inferior
vena cava
Ascending
lumbar vein
Median
cubital vein
Median
antebrachial
vein
Cephalic
vein
Radial
vein
Basilic vein
Ulnar vein
Deep palmar
venous arch
Superficial palmar
venous arch
Digital veins
(b)
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Figure 19.27b
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
(b)
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Figure 19.28b
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
(c)
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Figure 19.28c
Common iliac vein
Internal iliac vein
External iliac vein
Inguinal ligament
Femoral vein
Great saphenous
vein (superficial)
Great saphenous vein
Popliteal vein
Anterior tibial vein
Fibular (peroneal) vein
Popliteal vein
Fibular (peroneal)
vein
Anterior tibial vein
Small saphenous vein
(superficial)
Dorsalis pedis vein
Dorsal venous arch
Metatarsal veins
Plantar veins
(b)
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Posterior tibial vein
Plantar arch
Digital veins
(c)
Figure 19.29b, c