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Chapter 15
The Circulation of the
Blood
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Lesson 15.1
Structure and Function of Blood Vessel Circulation
and Related Disorders
Describe the structure and function of each major
type of blood vessel: artery, vein, and capillary.
2. List the major disorders of blood vessels and explain
how they develop.
3. Trace the path of blood through the systemic,
pulmonary, portal, and fetal circulations.
1.
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2
Blood Vessels
 Types
 Arteries—carry blood away from the heart and toward
capillaries
 Veins—carry blood toward the heart and away from
capillaries
 Capillaries—carry blood from the arterioles to the venules
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Structure of Blood Vessels
 Arteries
 Tunica intima—inner layer of endothelial cells
 Tunica media—smooth muscle, thick in arteries;
some elastic tissue; important in blood pressure
regulation
 Tunica externa—outer layer of fibrous
connective elastic tissue
 Capillaries—microscopic vessels
 Only one layer—the tunica intima
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Structure of Veins
 Tunica intima—inner layer; valves prevent
retrograde movement of blood
 Tunica media—smooth muscle; thin in veins
 Tunica externa—heavy layer of fibrous
connective tissue in many veins
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Artery and Vein
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Blood Vessels
 Functions
 Arteries—distribute
nutrients, gases, etc., carried
in the blood by way of high
pressure; assist in maintaining
the arterial blood pressure;
serve as blood reservoirs
 Capillaries—serve as
exchange vessels for nutrients,
wastes, and fluids
 Veins—collect blood for
return to the heart; lowpressure flow of blood
(compared to arteries)
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Principal Arteries of the Body
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Systemic
Arteries
Principal
systemic
arteries.
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Principal Veins of the Body
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Systemic Veins
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Disorders of Blood Vessels
 Disorders of arteries—arteries must withstand
high pressure and remain free of blockage
 Arteriosclerosis—hardening of arteries caused
by calcification of fatty deposits on arterial walls


Reduces flow of blood, possibly causing ischemia that
may progress to necrosis (or gangrene)
May be corrected by vasodilators (vessel-relaxing
drugs) or angioplasty (mechanical widening of
vessels), or surgical replacement
 Atherosclerosis—lipids and other matter block
arteries
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Partial Blockage of an Artery in
Atherosclerosis
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Balloon Angioplasty
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Disorders of Arteries

Aneurysm—abnormal
widening of arterial wall
• Promotes formation of
thrombi that may obstruct
blood flow to vital tissues
• Arterial walls may burst,
resulting in life-threatening
hemorrhaging
• Cerebrovascular accident
(CVA) or stroke—ischemia
(reduced blood flow) of brain
tissue caused by embolism or
hemorrhage
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Disorders of Veins
 Veins are low-pressure vessels
 Varicose veins (varices)—enlarged veins in which
blood pools


Hemorrhoids are varicose veins in the rectum
Treatments include supporting affected veins and
surgical removal of veins
 Thrombophlebitis—vein inflammation
(phlebitis) accompanied by clot (thrombus)
formation; may result in fatal pulmonary
embolism
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Varicose Veins
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Circulation of Blood
 Systemic and pulmonary circulation
 Blood circulation—refers to the flow of blood
through all the vessels, which are arranged in a
complete circuit or circular pattern
 Systemic circulation


Carries blood throughout the body
Path goes from left ventricle through aorta, smaller
arteries, arterioles, capillaries, venules, venae cavae, to
right atrium
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Diagram of Blood Flow in the
Circulatory System
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Pulmonary & Hepatic Portal Circulation
 Pulmonary circulation
 Carries blood to and from the lungs
 Arteries deliver deoxygenated blood to the lungs
for gas exchange
 Path goes from right ventricle through pulmonary
arteries, lungs, pulmonary veins, to left atrium
 Hepatic portal circulation
 Unique blood route through the liver
 Vein (hepatic portal vein) exists between two
capillary beds
 Assists with homeostasis of blood glucose levels
 Stores glycogen and detoxifies the blood
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Hepatic Portal Circulation
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Fetal Circulation
 Refers to circulation before birth
 Modifications required for fetus to efficiently
secure oxygen and nutrients from the maternal
blood
 Unique structures include the placenta,
umbilical arteries and vein, ductus venosus,
ductus arteriosus, and foramen ovale
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The Fetal Circulation
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Changes to Fetal Circulation at
Birth
 Baby's specialized fetal blood vessels must stop working
 When newborn first breathes air, the pressure exerted
closes off those vessels and the foramen ovale
 If the foramen ovale fails to close, ATRIAL SEPTAL
DEFECT (ASD) occurs, creating a lack of oxygen
 Resulting bluish tint is called cyanosis
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Congenital heart defects.
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Circulation Physiology
 Blood exchanges oxygen, carbon dioxide, other
substances generated by cells.
 Tissue fluid (interstitial fluid) is the exchange medium.
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Circulation Physiology (cont.)
Capillary Exchange
 How substances move between cells and capillary blood
 Diffusion

Main process
 Blood pressure

Moves material into the interstitial fluid (filtration)
 Osmotic pressure

Moves material from the interstitial fluid back into capillaries
(osmosis)
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Circulation Physiology
The role of capillaries.
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Circulation Physiology (cont.)
Return of Blood to the Heart
 Mechanisms that promote blood’s return to the heart
 Contraction of skeletal muscles
 Valves in the veins
 Breathing
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Circulation Physiology (cont.)
Blood return.
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Lesson 15.2
Blood Pressure and Hypertension, Pulse Points,
and Circulatory Shock
4. Identify and discuss the factors involved in the
generation of blood pressure and how they relate to
each other.
5. Define pulse and locate the major pulse points on the
body.
6. Define hypertension and its associated risk factors
and complications.
7. Explain what is meant by the term circulatory shock
and describe the major types.
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Blood Pressure
 Defining blood pressure
 “Push” or force of blood in the blood vessels
 Exists in all blood vessels—highest in arteries,
lowest in veins
 Blood pressure gradient—causes blood to
circulate; liquids can flow only from areas of high
pressure to areas of low pressure


Hypotension- Low or nonexistent blood pressure
gradient is fatal if not reversed
Hypertension- (high blood pressure) can cause a
blood vessel to rupture
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Pressure Gradients in Blood Flow
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Factors that Influence Blood Pressure
 Blood volume—the larger the volume, the more
pressure is exerted on vessel walls
 Strength of heart contractions—affect cardiac
output; stronger heartbeat increases pressure;
weaker beat decreases it
 Heart rate—increased rate increases pressure;
decreased rate decreases pressure
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Blood Viscosity and Resistance to Flow
 Blood viscosity (thickness)—less than normal
viscosity decreases pressure; more than normal
viscosity increases pressure
 Resistance to blood flow (peripheral
resistance)—affected by many factors, including
the vasomotor mechanism (vessel muscle
contraction/relaxation)
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Vasomotor Mechanism
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Fluctuations in Blood Pressure
 Blood pressure varies within normal range from time
to time
 Central venous pressure—influences pressure in
large peripheral veins
 Venous return of blood to the heart depends on five
mechanisms
 A strongly beating heart
 An adequate arterial blood pressure
 Valves in the veins
 Pumping action of skeletal muscles as they contract
 Changing pressures in the chest cavity caused by
breathing
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Pulse
 Definition—alternate expansion and recoil of the
blood vessel wall
 Nine major pulse points named after arteries over
which they are felt
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Pulse Points
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Hypertension (HTN)
 Occurs when blood pressure exceeds 140/90 mm
Hg
 Ninety percent of HTN cases are primary essential
(idiopathic); secondary HTN can be caused by
kidney disease or other causes
 Many risk factors for HTN, including genetics, age,
stress, obesity, and more
 Untreated HTN may contribute to heart disease,
kidney failure, and stroke
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Classification of Hypertension
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Circulatory Shock
 Failure of the circulatory system to deliver oxygen
to the tissues adequately, resulting in cell
impairment
 Cardiogenic shock—caused by heart failure
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Hypovolemic Shock
 Drop in blood volume that causes blood pressure
(and blood flow) to drop
 Often caused by hemorrhage or loss of interstitial
fluid, causing blood plasma to drain out of the
vessels
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Negative Feedback
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Neurogenic Shock
 Caused by nerve condition that relaxes (dilates)
blood vessels and thus reduces blood flow
 Occurs when sympathetic stimulation is disrupted
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Anapyhlactic Shock
 Results from an acute allergic reaction called
anaphylaxis
 Causes the same kind of blood vessel dilation that
occurs in neurogenic shock
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Septic Shock
 Results from complications of septicemia (toxins in
blood resulting from infection)
 Toxins dilate blood vessels, inducing shock
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