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Blood Vessels and Circulation
5 Classes of Blood Vessels
1. Arteries:
carry blood away from heart
2. Arterioles:
Are smallest branches of arteries
3. Capillaries:
are smallest blood vessels
location of exchange between blood and interstitial
4. Venules:
collect blood from capillaries
5. Veins:
return blood to heart
The Largest Blood Vessels
• Attach to heart
• Pulmonary trunk:
– carries blood from right ventricle
– to pulmonary circulation
• Aorta:
– carries blood from left ventricle
– to systemic circulation
The Smallest Blood Vessels
• Capillaries
• Have small diameter and thin walls
• Chemicals and gases diffuse across
Structure of Vessel Walls
Tunica Externa
In arteries:
In veins:
Figure 21-1
Arteries vs. Veins
• Arteries and veins run side-by-side
• Arteries have thicker walls and higher blood
• Collapsed artery has small, round lumen
• Vein has a large, flat lumen
• Vein lining contracts, artery lining does not
• Artery lining folds
• Arteries more elastic
• Veins have valves
Arteries and Pressure
• Elasticity allows arteries to absorb
pressure waves that come with each
• Contractility -Arteries change diameter
• Controlled by sympathetic division of
and Vasodilation
• Vasoconstriction -The contraction of
arterial smooth muscle by the ANS
• Vasodilatation- The relaxation of arterial
smooth muscle
Enlarging the lumen
• Both Affect:
– afterload on heart
– peripheral blood pressure
– capillary blood flow
Structure of Blood
Artery Characteristics
From heart to
capillaries, arteries
from elastic arteries
to muscular arteries
to arterioles
Figure 21-2
• Are small
• Have little or no tunica externa
• Have thin or incomplete tunica media
Artery Diameter
• Small muscular arteries and arterioles:
– changes with sympathetic or endocrine
– constricted arteries oppose blood flow
• Resistance (R) -The force opposing
blood flow
• Resistance vessels:
– arterioles
• A bulge in an arterial wall
• Is caused by weak spot in elastic fibers
• Pressure may rupture vessel
• Are smallest vessels with thin walls
• Microscopic capillary networks permeate
all active tissues
Capillary Function
• Location of all exchange functions of
cardiovascular system
• Materials diffuse between blood and
interstitial fluid
Capillary Structure
Figure 21-4
2 Types of Capillaries
1. Continuous capillaries-Have complete endothelial
Are found in all tissues except epithelia and
• Permit diffusion of:
Water, small solutes, Lipid-soluble materials
blood cells, plasma proteins
Are in CNS and thymus, Have very restricted
permeability e.g., the blood–brain barrier
2. Fenestrated capillaries-Have complete
endothelial lining
Are found in all tissues except epithelia and
cartilage, in choroid plexus, endocrine organs,
kidneys,intestinal tract
Capillary Networks
Capillary bed
or capillary
Connect 1
arteriole and
1 venule
Figure 21-5
Capillary Sphincter
• Guards entrance to each capillary
• Opens and closes, causing capillary
blood to flow in pulses
• Vasomotion -Contraction and
relaxation cycle of capillary sphincters
• Causes blood flow in capillary beds to
constantly change routes
• Collect blood from capillaries in tissues
and organs
• Return blood to heart
Veins vs. Arteries
• Are larger in diameter
• Have thinner walls
• Carry lower blood pressure
1. Venules:
3 Vein Categories
very small veins
collect blood from capillaries
2. Medium-sized veins:
thin tunica media and few smooth muscle cells
tunica externa with longitudinal bundles of
elastic fibers
3. Large veins:
have all 3 tunica layers
thick tunica externa
thin tunica media
Valves in the Venous System
Vein Valves
Folds of tunica intima
Prevent blood from
flowing backward
Compression pushes blood
toward heart
Figure 21-6
Blood Distribution
Heart, arteries,
and capillaries:
30–35% of
blood volume
Venous system:
Figure 21-7
Venous Blood Distribution
• 1/3 of venous blood is in the large
venous networks of the liver, bone
marrow, and skin
Cardiovascular Physiology
Figure 21-8
Cardiovascular Regulation
• Maintains capillary blood flow in
peripheral tissues and organs
Capillary Blood Flow
• Equals cardiac output
• Is determined by:
– pressure and resistance in the
cardiovascular system
Measuring Pressure
• Blood pressure (BP):
– arterial pressure (mm Hg)
• Capillary hydrostatic pressure (CHP):
– pressure within the capillary beds
• Venous pressure:
– pressure in the venous system
InterActive Physiology: Cardiovascular
System: Measuring Blood Pressure
• R caused by molecules and suspended
materials in a liquid
• Whole blood viscosity is about 4 times
that of water
• Swirling action that disturbs smooth
flow of liquid
• Occurs in heart chambers and great
• Atherosclerotic plaques cause
abnormal turbulence
Pressures in the
Systemic Circuit
• Systolic pressure:
– peak arterial pressure during ventricular systole
• Diastolic pressure:
– minimum arterial pressure during diastole
• Pulse pressure:
– difference between systolic pressure and
diastolic pressure
• Mean arterial pressure (MAP):
MAP = diastolic pressure + 1/3 pulse pressure
Abnormal Blood Pressure
• Hypertension:
– abnormally high blood pressure:
• greater than 140/90
• Hypotension:
– abnormally low blood pressure
Venous Return
• Amount of blood arriving at right atrium
each minute
• Determined by venous pressure
• Low effective pressure in venous system
• Low venous resistance Is assisted by:
– muscular compression of peripheral veins
– the respiratory pump
• Compression of skeletal muscles:
– pushes blood toward heart (one-way valves)
Capillary Exchange
• Vital to homeostasis
• Moves materials across capillary walls
– diffusion, filtration, and reabsorption
5 Diffusion Routes
1. Water, ions, and small molecules such as
diffuse between adjacent endothelial cells
or through fenestrated capillaries
diffuse through channels in cell membranes
2. Some ions ( Na+, K+, Ca2+, Cl—):
3. Large, water-soluble compounds:
pass through fenestrated capillaries
4. Lipids and lipid-soluble materials such as O2 and
diffuse through endothelial cell membranes
5. Plasma proteins:
cross endothelial lining in sinusoids
Capillary Filtration
Figure 21-11
Capillary Exchange
• At arterial end of capillary:
– fluid moves out of capillary
– into interstitial fluid
• At venous end of capillary:
– fluid moves into capillary
– out of interstitial fluid
The Transition Point
• Between filtration and reabsorption
– is closer to venous end than arterial end
• Capillaries filter more than reabsorb
• Excess fluid enters lymphatic vessels
4 Functions of
Blood and Lymph Cycle
1. Ensures constant plasma and interstitial
fluid communication
2. Accelerates distribution of nutrients,
hormones, and dissolves gases through
Transports insoluble lipids and tissue proteins
that can’t cross capillary walls
4. Flushes bacterial toxins and chemicals to
immune system tissues
Capillary Dynamics
• Hemorrhaging:
– reduces CHP and NFP
– increases reabsorption of interstitial fluid
(recall of fluids)
• Dehydration:
– increases BCOP
– accelerates reabsorption
• Increase in CHP or BCOP:
– fluid moves out of blood
– builds up in peripheral tissues (edema)
• Blood flow is the goal
• Total peripheral blood flow equals cardiac
• Blood pressure overcomes friction and elastic
forces to sustain blood flow
• If blood pressure is too low:
– vessels collapse, blood flow stops
– tissues die
• If blood pressure is too high:
– vessel walls stiffen, capillary beds may rupture
How do central and
local control mechanisms
interact to regulate blood
flow and pressure in tissues?
Tissue Perfusion
• Blood flow through the tissues
• Carries O2 and nutrients to tissues and
• Carries CO2 and wastes away
• Is affected by:
– cardiac output
– peripheral resistance
– blood pressure
3 Regulatory Mechanisms
• Control cardiac output and blood
1. Autoregulation:
• causes immediate, localized homeostatic
Neural mechanisms:
• respond quickly to changes at specific sites
3. Endocrine mechanisms:
• direct long-term changes
Dilate precapillary sphincters
Local vasodilators:
accelerate blood flow at tissue level
Low O2 or high CO2 levels
Low pH (acids),Nitric oxide (NO)
High K+ or H+ concentrations
Chemicals released by inflammation
5. Elevated local temperature
Patterns of
Cardiovascular Response
• Blood, heart, and cardiovascular
– work together as unit
– respond to physical and physiological
changes (e.g., exercise, blood loss)
– to maintain homeostasis
Blood Distribution
during Exercise
Table 21-2
3 Effects of Light Exercise
1. Extensive vasodilation occurs:
increasing circulation
2. Venous return increases:
with muscle contractions
3. Cardiac output rises:
due to rise in venous return (Frank–
Starling principle) and atrial stretching
5 Effects of Heavy Exercise
1. Activates sympathetic nervous system
2. Cardiac output increases to maximum:
about 4 times resting level
3. Restricts blood flow to “nonessential”
organs (e.g., digestive system)
4. Redirects blood flow to skeletal muscles,
lungs, and heart
5. Blood supply to brain is unaffected
Training and
Cardiovascular Performance
Effects of Exercise
Regular moderate exercise:
lowers total blood cholesterol levels
Intense exercise:
can cause severe physiological stress
Table 21-3
Responses to Blood Loss
Figure 21-17
Responses to Severe Blood Loss
• Also called hemorrhaging
• Entire cardiovascular system adjusts to:
– maintain blood pressure
– restore blood volume
• To prevent drop in blood pressure:
1. carotid and aortic reflexes:
• increase cardiac output (increasing heart rate)
• cause peripheral vasoconstriction
Sympathetic nervous system:
• triggers hypothalamus
• further constricts arterioles
• venoconstriction improves venous return
3 Short-Term
Responses to Hemorrhage
• To prevent drop in blood pressure:
1. carotid and aortic reflexes:
• increase cardiac output (increasing heart rate)
• cause peripheral vasoconstriction
2. Sympathetic nervous system:
• triggers hypothalamus
• further constricts arterioles
• venoconstriction improves venous return
3. Hormonal effects:
• increase cardiac output
• increase peripheral vasoconstriction (E, NE, ADH,
angiotensin II)
• Short-term responses compensate up
to 20% loss of blood volume
• Failure to restore blood pressure
results in shock
Circulatory Shock
4 Long-Term
Responses to Hemorrhage
• Restoration of blood volume can take
several days:
1. Recall of fluids from interstitial spaces
2. Aldosterone and ADH promote fluid
retention and reabsorption
3. Thirst increases
4. Erythropoietin stimulates red blood cell
What are the principle
blood vessels and functional
characteristics of the
special circulation to the
brain, heart, and lungs?
Blood Flow to the Brain
• Is top priority
• Brain has high oxygen demand
• When peripheral vessel constrict,
cerebral vessels dilate, normalizing
blood flow
• Also called cerebrovascular accident
• Blockage or rupture in a cerebral
• Stops blood flow
Blood Flow to the Heart
• Through coronary arteries
• Oxygen demand increases with activity
• Lactic acid and low O2 levels:
– dilate coronary vessels
– increase coronary blood flow
• Epinephrine:
– dilates coronary vessels
– increases heart rate
– strengthens contractions
Heart Attack
• A blockage of coronary blood flow
• Can cause:
tissue damage
heart failure
Blood Flow to the Lungs
• Regulated by O2 levels in alveoli
• High O2 content:
– vessels dilate
• Low O2 content:
– vessels constrict
Pulmonary Blood Pressure :
• In pulmonary capillaries:
– is low to encourage reabsorption
• If capillary pressure rises:
– pulmonary edema occurs
Circulation Patterns
3 Distribution Patterns:
1. Peripheral artery and vein
is the same on right and left,
except near the heart
2. The same vessel: may have
different names in different
3. Tissues and organs usually have
multiple arteries and veins:
vessels may be interconnected
by anastomoses
Figure 21-18
The Pulmonary Circuit
Figure 21-19
The Pulmonary Circuit
1. Deoxygenated blood arrives at heart from
systemic circuit:
passes through right atrium and ventricle
enters pulmonary trunk
2. At the lungs:
CO2 is removed
O2 is added
3. Oxygenated blood:
returns to the heart
is distributed to systemic circuit
Pulmonary Vessels
• Pulmonary arteries:
– carry deoxygenated blood
• Pulmonary veins:
– carry oxygenated blood
Pulmonary Arteries
• Pulmonary trunk:
– branches to left and right pulmonary
• Pulmonary arteries:
– branch into pulmonary arterioles
• Pulmonary arterioles:
– branch into capillary networks that
surround alveoli
Pulmonary Veins
• Capillary networks around alveoli:
– join to form venules
• Venules:
– join to form 4 pulmonary veins
• Pulmonary veins:
– empty into left atrium
Major Systemic Arteries
The Systemic Circuit
Contains 84% of
blood volume
Supplies entire body:
except for
pulmonary circuit
Figure 21-20
Arteries of the Chest
and Upper Limbs
3D Peel-Away of Arteries
of the Upper Limbs
Figure 21-21a, b
Systemic Arteries
• Blood moves from left ventricle:
– into ascending aorta
• Coronary arteries:
– branch from aortic sinus
The Aorta
• The ascending aorta:
– rises from the left ventricle
– curves to form aortic arch
– turns downward to become descending aorta
• Branches of the Aortic Arch deliver blood to
head and neck:
– brachiocephalic trunk
– left common carotid artery
– left subclavian artery
• The Brachiocephalic Trunk Branches to
– right subclavian artery
– right common carotid artery
• The Subclavian Arteries Branches within
thoracic cavity:
– internal thoracic artery
– vertebral artery
– thyrocervical trunk
The Subclavian Arteries
• The Subclavian Arteries Branches within
thoracic cavity:
– internal thoracic artery
– vertebral artery
– thyrocervical trunk
• Leaving the thoracic cavity:
– become axillary artery in arm
– and brachial artery distally- Divides at
coronoid fossa of humerus:
– into radial artery and ulnar artery
Arteries of the Neck and Head
3D Peel-Away of Arteries of the
Head and Neck
Figure 21-22
The Common Carotid Arteries
• Carry blood to head and neck
• Each common carotid divides into:
– external carotid artery-Supplies structures
of: Neck, lower jaw, face
– internal carotid artery-Enters skull and
divides into: opthalmic artery, anterior
cerebral artery, middle cerebral artery
Arteries of the Brain
Figure 21-23
The Vertebral Arteries
• Also supply brain with blood supply
• Left and right vertebral arteries:
– arise from subclavian arteries
– enter cranium through foramen magnum
– fuse to form basilar artery
Arteries of the Trunk
Aorta - is
divided by
diaphragm into:
thoracic aorta
Figure 21-24a
Arteries of the Trunk
Thoracic Aorta
branches are
grouped into:
3D Peel-Away of Arteries of the Trunk
Figure 21-24b
4 Visceral Branches
• Supply organs of the chest:
bronchial arteries
pericardial arteries
esophogeal arteries
mediastinal arteries
The Abdominal Aorta
• Divides at terminal segment of the
aorta into:
– left common iliac artery
– right common iliac artery
Branches of the Abdominal Aorta
• Unpaired branches:
– major branches to visceral organs
• Paired branches:
to body wall
urinary bladder
structures outside abdominopelvic cavity
Arteries of the
Abdominopelvic Organs
Figure 21-25
3 Unpaired Branches
of the Abdominal Aorta
• Celiac trunk, divides into:
– left gastric artery
– splenic artery
– common hepatic artery
• Superior mesenteric artery
• Left mesenteric artery
5 Paired Branches of
the Abdominal Aorta
Inferior phrenic arteries
Suprarenal arteries
Renal arteries
Gonadal arteries
Lumbar arteries
The Abdominal Aorta
• Divides to form:
– right and left common iliac arteries –
Divide to form: internal iliac artery,
external iliac artery
– middle sacral artery-
Arteries of the Lower Limbs
3D Peel-Away of Arteries
of the Lower Limbs
Figure 21-26
Major Systemic Veins
All Systemic Veins
Drain into either:
superior vena
cava (SVC)
or inferior vena
cava (IVC)
Figure 21-27
Arteries and Veins
• Run side by side
• Branching patterns of peripheral veins
are more variable
Differences in Artery
and Vein Distribution
• In neck and limbs:
– 1 set of arteries (deep)
– 2 sets of veins (1 deep, 1 superficial)
• Venous system controls body
Veins of the Head,
Neck, and Brain
Figure 21-28
The Superior Vena Cava (SVC)
• Receives blood from:
upper limbs
Veins of the Neck
• Temporal and maxillary veins:
– drain to external jugular vein
• Facial vein:
– drains to internal jugular vein
Veins of the Abdomen and Chest
Figure 21-29
Deep Veins of the Forearm
• Deep palmar veins drain into:
– radial and ulnar veins
– which fuse above elbow to form brachial
• Veins of the Upper Arm Cephalic vein
joins axillary vein:
– to form subclavian vein
The Subclavian Vein
• Merges with external and internal
jugular veins:
– to form brachiocephalic vein
– which enters thoracic cavity
Veins of the Thoracic Cavity
• Brachiocephalic vein receives blood
vertebral vein
– internal thoracic vein
• Merge to form the superior vena cava
Tributaries of the
Superior Vena Cava
Figure 21-30a
Tributaries of the
Inferior Vena Cava
•Inferior Vena Cava
collects blood from
organs inferior to the
Figure 21-30b
Veins of the Lower Limbs
Figure 21-31
The Femoral Vein
• Before entering abdominal wall, receives
blood from:
– great saphenous vein
– deep femoral vein
– femoral circumflex vein
• Inside the pelvic cavity:
– becomes the external iliac vein
• The Right and Left Common Iliac Veins
Merge to form the inferior vena cava
Veins of the Abdomen
6 Major Tributaries
of the
Inferior Vena
Lumbar veins
Gonadal veins
Hepatic veins
Renal veins
Suprarenal veins
Figure 21-29
The Hepatic Portal System
Figure 21-32
The Hepatic Portal System
• Connects 2 capillary beds
• Delivers nutrient-laden blood:
– from capillaries of digestive organs
– to liver sinusoids for processing
5 Tributaries of the
Hepatic Portal Vein
1. Inferior mesenteric vein:
drains part of large intestine
2. Splenic vein:
drains spleen, part of stomach, and pancreas
3. Superior mesenteric vein:
drains part of stomach, small intestine, and part
of large intestine
4. Left and right gastric veins:
drains part of stomach
5. Cystic vein:
drains gallbladder
Blood Processed in Liver
• After processing in liver sinusoids,
blood collects in hepatic veins and
empties into inferior vena cava
Fetal Circulation
• Embryonic lungs and digestive tract
• Respiratory functions and nutrition
provided by placenta
Placental Blood Supply
Blood flows to the placenta:
through a pair of umbilical
which arise from internal
iliac arteries
and enter umbilical cord
Blood returns from placenta:
in a single umbilical vein
which drains into ductus
Ductus venosus:
empties into inferior vena
Figure 21-33a
The Neonatal Heart
Before Birth -Fetal
lungs are collapsed
O2 provided by
placental circulation
At Birth -Newborn
breathes air
Lungs expand
Pulmonary circulation
provides O2
Figure 21-33b
2 Fetal Pulmonary
Circulation Bypasses
1. Foramen ovale:
interatrial opening
covered by valve-like flap
directs blood from right to left atrium
2. Ductus arteriosus:
short vessel
connects pulmonary and aortic trunks
Cardiovascular Changes at Birth
• Pulmonary vessels expand
• Reduced resistance allows blood flow
• Rising O2 causes ductus arteriosus
• Rising left atrium pressure closes
foramen ovale
Cardiovascular Problems
Develop if proper circulatory changes do not occur at
Figure 21-34
Aging and the
Cardiovascular System
• Cardiovascular capabilities decline
with age
• Age-related changes occur in:
– blood
– heart
– blood vessels
3 Age-Related Changes in Blood
1. Decreased hematocrit
2. Blood clots (thrombus)
3. Blood-pooling in legs
due to venous valve deterioration
5 Age-Related
Changes in the Heart
Reduced maximum cardiac output
Changes in nodal and conducting cells
Reduced elasticity of fibrous skeleton
Progressive atherosclerosis
Replacement of damaged cardiac
muscle cells by scar tissue
3 Age-Related
Changes in Blood Vessels
1. Arteries become less elastic:
pressure change can cause aneurysm
2. Calcium deposits on vessel walls:
can cause stroke or infarction
3. Thrombi can form:
at atherosclerotic plaques
Integration with Other Systems
Figure 21-35
Clinical Patterns
• There are many categories of
cardiovascular disorders
• Disorders may:
– affect all cells and systems
– be structural or functional
– result from disease or trauma
• 3 types of blood vessels:
– arteries
– veins
– Capillaries
Structure of vessel walls
Differences between arteries and veins
Atherosclerosis, arteriosclerosis, and plaques
Structures of:
– elastic arteries
– muscular arteries
– arterioles
• Structures of capillary walls:
– continuous
– Fenestrated
• Structures of capillary beds:
– precapillary sphincters
– vasomotion
– arteriovenous anastomoses
• Functions of the venous system and valves
• Distribution of blood and venous reserves
• Circulatory pressures:
– blood pressure
– capillary hydrostatic pressure
– venous pressure
• Resistance in blood vessels:
– viscosity
– turbulence
– Vasoconstriction
• The respiratory pump
• Capillary pressure and capillary exchange:
– osmotic pressure
– net filtration pressure
• Physiological controls of cardiovascular system:
– Autoregulation, neural controls
– hormonal controls
• Cardiovascular responses to exercise and blood loss
• Special circulation to brain, heart, and lungs
• Distribution of arteries in pulmonary and systemic
• Distribution of veins in pulmonary and systemic
• Fetal circulation and changes at birth
• Effects of aging on the cardiovascular system