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CHAPTER
8
Circulatory Systems
PowerPoint® Lecture Slides prepared by
Stephen Gehnrich, Salisbury University
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Limits of Diffusion
 Unicellular organisms and some small metazoans
lack circulatory systems
 Rely on diffusion to transport molecules
 Diffusion can be rapid over small distances, but is
very slow over large distances
 Large animals move fluid through their bodies by
bulk flow, or convective transport
 Transport can occur over greater distance
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Evolution of Circulatory Systems
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Figure 8.8
Diffusion vs. Bulk Flow
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Figure 8.1
Overview
 Most metazoans larger than a few cells have
circulatory systems
 Major function
 Transport oxygen, carbon dioxide, nutrients, waste
products, immune cells, and signaling molecules
throughout the body
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Components of Circulatory Systems
 Circulatory systems move fluids by increasing the
pressure of the fluid in one part of the body
 Fluid flows through the body, “down” the pressure
gradient
 Three main components are needed
 Pump or propulsive structures
 For example, a heart
 System of tubes, channels, or spaces
 Fluid that circulates through the system
 For example, blood
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Types of Pumps
 Chambered hearts
 Contractile chambers
 Blood enters atrium
 Blood is pumped out by ventricle
 Skeletal muscle
 Squeeze on vessels to generate pressure
 Pulsating blood vessels
 Peristalsis
 Rhythmic contractions of vessel wall pumps blood
 One-way valves help to ensure unidirectional flow
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Types of Pumps
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Figure 8.2
Closed and Open Circulatory Systems
 Closed
 Circulatory fluid remains within vessels and does not
come in direct contact with the tissues
 Circulating fluid is distinct from interstitial fluid
 Molecules must diffuse across vessel wall
 Open
 Circulatory fluid comes in direct contact with the
tissues in spaces called sinuses
 Circulating fluid mixes with interstitial fluid
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Types of Fluid
 Interstitial fluid
 Extracellular fluid that directly bathes the tissues
 Blood
 Fluid that circulates within the vessels of a closed
circulatory system
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Types of Fluid
 Lymph
 Fluid that circulates in the secondary circulatory
system of vertebrates; the lymphatic system
 Carries fluid (lymph) that has filtered out of the
vessels
 Hemolymph
 Fluid that circulates in an open circulatory system
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Some Animals Lack Circulatory Systems
 Sponges, cnidarians, and flatworms
 Lack circulatory systems but have mechanisms for
propelling fluids around their bodies
 Sponges
 Flagellated choanocytes
 Cnidarians
 Muscular contractions of the body wall pump water in
and out of body cavity
 Flatworms
 Ciliated cells move water within body cavity
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Some Animals Lack Circulatory Systems
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Figure 8.3
Annelids
 Three main classes of annelids
 Polychaeta (tube worms)
 Oligochaeta (earth worms)
 Hirudinea (leeches)
 Polychaetes and oligochaetes circulate interstitial
fluid with cilia or muscular contractions of body
wall
 Most have vessels that circulate fluid with oxygen
carrier protein
 Circulatory system can be an open (polychaetes) or
closed (oligochaetes)
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Annelids
 Polychaeta (tube worms)
 Oligochaeta (earth worms)
 Hirudinea (leeches)
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Annelids
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Figure 8.4
Molluscs
 All have hearts and
some blood vessels
 Most have open
systems
 Only cephalopods
have closed systems
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Figure 8.5
Arthropods
 All have one or more hearts and some blood vessels
 All have open systems
 No arthropods have a closed system
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Arthropods – Crustaceans
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Figure 8.6
Fairy shrimp
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Arthropods – Insects
 Relatively simple open
circulatory system
 Multiple, contractile
“hearts” along dorsal
vessel
 Insects use a tracheal
system for most gas
transport
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Figure 8.7
Chordates
 Phylum Chordata includes two invertebrate groups
and vertebrates
 Urochordates (tunicates)
 Open circulatory system
 Tubular heart at the base of the digestive tract
 Cephalochordates (lancelets)
 Closed system with a few open sinuses
 Tubular heart at the base of the digestive tract and
pulsatile blood vessels
 Vertebrates (fish, amphibian, reptiles, birds,
mammals)
 All vertebrates have closed systems
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Tunicates
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Lancelets
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Evolution of Circulatory Systems
 First evolved to transport nutrients to body cells
 Very early began to serve respiratory function
 Closed systems evolved independently in vertebrates,
cephalopods, and annelids
 Increased blood pressure and flow
 Increased control of blood distribution
 Closed systems evolved in combination with
specialized oxygen carrier molecules
 High metabolic rates
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Evolution of Circulatory Systems
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Figure 8.8
The Circulatory Plan of Vertebrates
 Muscular, chambered heart contracts to increase the
pressure of the blood
 Blood flows away from the heart in arteries
 Arteries branch to form more numerous, but smaller
diameter, arteries
 Small arteries branch into arterioles within tissues
 Blood flows from arterioles into capillaries
 Capillaries are the site of diffusion of molecules
between blood and interstitial fluid
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p357
The Circulatory Plan of Vertebrates
 Capillaries coalesce to form venules
 Venules coalesce to form veins
 Veins carry blood to the heart
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The Circulatory Plan of Vertebrates
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Figure 8.9
Vertebrate Blood Vessels
 A complex wall surrounding a central lumen
 Wall composed of up to three layers
 Tunica intima (internal lining)
 Smooth, epithelial cells ( subendothelium)
 Vascular endothelium
 Tunica media (middle layer)
 Smooth muscle
 Elastic connective tissue
 Tunica externa (outermost layer)
 Collagen
 Thickness of the wall varies among vessels
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Vertebrate Blood Vessels
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Figure 8.10
Capillaries
 Lack tunica media and tunica externa
 Continuous
 Cells held together by tight junctions
 Skin and muscle
 Fenestrated
 Cells contain pores
 Specialized for exchange
 Kidneys, endocrine organs, and
intestine
 Sinusoidal
 Few tight junctions
 Most porous for exchange of large
proteins
 Liver and bone marrow
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Figure 8.11
Vertebrates
 All have a closed system
 Structure varies depending on respiratory strategy
 Water-breathing fish
 Single circuit
 Some fish have accessory hearts in the tail
 Air-breathing tetrapods
 Two circuits
 Pulmonary circuit – right side of heart
 Systemic circuit – left side of heart
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Circulatory Patterns of Vertebrates
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Figure 8.12
Birds and Mammals
 Four-chambered heart
 Two atria
 Two ventricles
 Systemic and pulmonary circuits are divided
 Pressure can be different in the two circuits
 High pressure systemic
 Low pressure pulmonary
 Oxygenated and deoxygenated blood are
completely separate
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Birds and Mammals
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Figure 8.12b
Amphibians and Reptiles
 Heart is only partially divided
 Two atria and one ventricle
 A three-chambered heart
 Blood from both atria flow into the ventricle
 Oxygenated and deoxygenated blood can mix
 Oxygenated and deoxygenated blood are kept fairly
separate by a mechanism that is not completely
understood
 Ventricle pumps blood into pulmonary and systemic
circuits
 Blood can be diverted between pulmonary and systemic
circuits
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Amphibians and Reptiles
 Crocodilians have completely divided ventricles
 Such as, a four-chambered heart
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Figure 8.13
Physics of Blood Flow
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Physics of Blood Flow
Law of bulk flow: Q = DP/R
Q = flow
DP = pressure drop
R = resistance
R = 8Lh /pr4
L = length of the tube
h = viscosity of the fluid
r = radius of the tube
vasoconstriction / vasodilation
Poiseuille’s equation: Q = DPp r4 / 8Lh
 More detailed version of law of bulk flow
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Modeling Circulatory Systems
 Like electrical
resistors, blood vessels
can be arranged in
series or parallel
 Resistors in series
 RT = R1 + R2…
 Resistors in parallel
 1/RT = 1/R1 + 1/R2…
 Because of the law of
conservation of mass,
the flow through each
segment of the system
must be equal
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Figure 8.14
Blood Velocity
 Flow (Q)
 Volume of fluid transferred per unit time
 Velocity
 Distance per unit time
 Blood velocity = Q/A
 A = cross-sectional area of the channels
 Velocity of flow is inversely related to total crosssectional area
 For example, total cross-sectional area of capillaries is very
large  velocity is slow  long time for diffusion
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Transmural Pressure
 Pressure exerts a force across vessel wall
 Law of LaPlace
 T = a Pr
 T = tension in vessel wall
 a = constant
 0.5 for a vessel
 1.0 for a chamber
 P = transmural pressure
 difference between
internal and
external pressure
 r = vessel radius
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Figure 8.15
Hearts
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Hearts
 Cardiac cycle – pumping action of the heart
 Two phases
 Systole
 Contraction
 Blood is forced out into the circulation
 Diastole
 Relaxation
 Blood enters the heart
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Arthropod Heart
 Heart pumps hemolymph
out via arteries
 Blood returns via ostia
(holes) during diastole
 Valves in the ostia open
and close to regulate flow
 The heart is suspended
with a series of ligaments
 The heart is neurogenic
 Contraction in response to
signals from nervous
system
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Figure 8.16
Cardiac Cycle in Arthropods
Neurons of cardiac ganglion undergo spontaneous
rhythmic depolarization








Cardiomyocytes contract
Volume of heart decreases; pressure increases
Valves in ostia close as pressure increases
Blood leaves the heart via arteries
Stretched ligaments pull apart walls of heart
Volume of heart increases; pressure decreases
Valves in ostia open
Blood is sucked into heart
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Vertebrate Hearts
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Vertebrate Hearts
 Complex walls with four main parts
 Pericardium
 Sac of connective tissue that surrounds heart
 Outer (parietal ) and inner (visceral) layers
 Space between layers filled with lubricating fluid
 Epicardium
 Outer layer of heart, continuous with visceral pericardium
 Contain nerves that regulate heart and coronary arteries
 Myocardium
 Layer of heart muscle cells (cardiomyocytes)
 Endocardium
 Innermost layer of connective tissue covered by epithelial
cells (called endothelium)
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Myocardium
 Two types of myocardium
 Compact
 Tightly packed cells arranged in regular pattern
 Spongy
 Meshwork of loosely connected cells
 Relative proportions vary among species
 Mammals
 Mostly compact
 Fish and amphibians
 Mostly spongy
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Myocardium
Vertebrate Hearts
Fish Hearts
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Figure 8.17
Fish Hearts
 Four chambers
arranged in series
 Sinus venosus
 Atrium
 Ventricle
 Bulbus arteriosus
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Figure 8.18a
Amphibian Hearts
 Three-chambered heart
 Two atria, one ventricle
 Trabeculae in ventricle
 Helps prevent mixing of
oxygenated and
deoxygenated blood in
ventricle
 Spiral fold in conus
arteriosus
 Helps direct deoxygenated
blood to pulmocutaneous
circuit and oxygenated
blood to systemic circuit
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Figure 8.18b
Reptile Hearts
 Five-chambered heart
 Two atria
 Three interconnected ventricular compartments
 Cavum venosum
 Leads to systemic aortas
 Cavum pulmonale
 Leads to pulmonary artery
 Cavum arteriosum
 Separation of oxygenated and deoxygenated blood in the
ventricle is nearly complete
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Reptile Hearts
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Figure 8.19a
Shunting in Reptile Hearts
 Can shunt blood to bypass pulmonary or systemic circuit
 Right-to-left shunt
 Deoxygenated blood bypasses pulmonary circuit and enters systemic
circuit
 During breath-holding
 Left-to-right shunt
 Oxygenated blood reenters pulmonary circuit
 Aids oxygen delivery to myocardium in right heart
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Shunting in Reptile Hearts
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+
Figure 8.19a,b
Birds and Mammals
 Four chambers
 Two atria
 Thin-walled
 Two ventricles
 Thick-walled
 Ventricles separated
by intraventricular
septum
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Figure 8.20
Birds and Mammals
 Valves
 Atrioventricular (AV)
valves
 Between atria and
ventricles
 Tricuspid on right
 Bicuspid on left
 Semilunar valves
 Between ventricles
and arteries
 Aortic between left
ventricle and aorta
 Pulmonary between
right ventricle and
pulmonary artery
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Figure 8.20
Cardiac Cycle
 Fish hearts
 Serial contractions of
chambers
 Valves are passive
 Opens and closes
according to pressure
differences
 Assure unidirectional
flow of blood
 In teleosts, noncontractile
bulbus arteriosus serves as
volume and pressure
reservoir
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Figure 8.18a
Mammalian Cardiac Cycle
 Atria and ventricles alternate systole and diastole
 The two atria contract simultaneously
 There is a slight pause
 The two ventricles contract simultaneously
 Atria and ventricles relax while the heart fills with
blood
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Mammalian Cardiac Cycle
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Figure 8.21
Ventricular Pressure
 Left ventricle contracts more forcefully and
develops higher pressure
 Resistance in pulmonary circuit low due to high
capillary density in parallel
 Large cross-sectional area
 Less pressure needed to pump blood through
pulmonary circuit
 Low pressure protects delicate blood vessels of
lung
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Ventricular Pressures
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Figure 8.22
Control of Contraction
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p375
Control of Contraction
 Vertebrate hearts are myogenic
 Cardiomyocytes produce spontaneous rhythmic
depolarizations
 Do not require nerve signal
 Cardiomyocytes are electrically coupled via gap
junctions to ensure coordinated contractions
 Action potential passes directly from cell to cell
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Control of Contraction
 Pacemaker
 Cells with fastest intrinsic rhythm
 In the sinus venosus in fish
 In the right atrium of other vertebrates
 Sinoatrial (SA) node
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Pacemaker Cells
 Derived from
cardiomyocytes
 Characteristics of
pacemaker cells
 Small with few myofibrils,
mitochondria, or other
organelles
 Have unstable resting
membrane potential
(pacemaker potential) that
drifts upwards until it
reaches threshold and
initiates an action potential
P: permeability
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Figure 8.23
Control of Pacemaker Potentials
 Increasing heart rate
 Norepinephrine released from sympathetic neurons
and epinephrine released from the adrenal medulla
 More Na+ and Ca2+ channels open
 Rate of depolarization and frequency of action
potentials increase
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p377
Increasing Heart Rate
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Figure 8.24
Control of Pacemaker Potentials
 Decreasing heart rate
 Acetylcholine released from parasympathetic neurons
 More K+ channels open
 Pacemaker cells hyperpolarize
 Frequency of action potentials decreases
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Decreasing Heart Rate
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Figure 8.25
Extended Action Potentials
 Action potentials in
cardiomyocytes differ from
those in skeletal muscle
 Plateau phase
 Extended depolarization that
corresponds to refractory
period and lasts as long as
the contraction
 Caused by Ca2+ entry via
L-type channel
 Prevents tetanus
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Figure 8.26
Conducting Pathways in Mammalian Heart
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Figure 8.27
Electrocardiogram (ECG or EKG)
 Composite recording of
action potentials in cardiac
muscle
 P wave
 Atrial depolarization
 QRS complex
 Ventricular
depolarization
 T wave
 Ventricular
repolarization
 Used for clinical diagnosis
of problems with
conducting system
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Figure 8.28
Electrical and Mechanical Events in the
Cardiac Cycle
 Heart functions as an integrated organ
 Electrical and mechanical events are correlated
 Changes in pressure and volume of chambers
 Blood flow through chambers
 Heart sounds
 Opening and closing of valves
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Electrical and Mechanical Events in the
Cardiac Cycle
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Figure 8.29
Cardiac Output
 Cardiac output (CO)
 Volume of blood pumped per unit time
 CO = HR  SV
 Rate of contraction (beats per minute)
 Stroke volume (SV)
 Volume of blood pumped with each beat
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Cardiac Output
CO = HR  SV
 Cardiac output can be modified by regulating heart
rate and/or stroke volume
 Heart rate
 Modulated by autonomic nerves and adrenal medulla
 Decreased HR (bradycardia)
 Increased HR (tachycardia)
 Stroke volume
 Modulated by various nervous, hormonal, and physical
factors
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Control of Stroke Volume
 Nervous and endocrine systems can cause the
heart to contract more forcefully and pump more
blood with each beat
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Figure 8.30
Control of Stroke Volume
 Frank-Starling effect
 Increased enddiastolic volume
results in a more
forceful contraction
and increased SV
 Length-tension
relationship for
muscle
 Heart automatically
compensates for
increases in volume of
blood returning to the
heart (autoregulation)
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Figure 8.31a
Control of Stroke Volume
Level of sympathetic activity shifts the position of
the cardiac muscle length-tension relationship
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Figure 8.31b
Regulation of Blood Flow
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Regulation of Blood Flow
 Arterioles control blood distribution
 Because arterioles are arranged in parallel, they can
alter blood flow to various organs
 Vasoconstriction and vasodilation
 Changes in resistance alter flow
 Control of vasoconstriction and vasodilation
 Autoregulation
 Direct response of the arteriole smooth muscle
 Intrinsic factors
 Metabolic state of the tissue
 Extrinsic factors
 Nervous and endocrine systems
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Myogenic Autoregulation of Flow
 Some smooth muscle cells in arterioles are
sensitive to stretch and contract when blood
pressure increases
 Acts as negative feedback loop
 Prevents excessive flow of blood into tissue
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Metabolic Activity of Tissues
 Smooth muscle cells in
arterioles sensitive to
conditions of extracellular fluid
 Levels of metabolites alter
vasoconstriction/vasodilation
 Blood flow matched to
metabolic requirements
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Figure 8.32
Neural and Endocrine Control of Flow
 Norepinephrine from sympathetic neurons causes
vasoconstriction
 Decreased sympathetic tone causes vasodilation
 Other hormones affect vascular smooth muscle
 Vasopressin (ADH) from the posterior pituitary causes
generalized vasoconstriction
 Angiotensin II produced in response to decreased
blood pressure causes generalized vasoconstriction
 Arterial natriuretic peptide (ANP) produced in
response to increased blood pressure promotes
generalized vasodilation
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Control of Vasoconstriction/Vasodilation
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Table 8.1
Regulation of Pressure
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P 388
Pressure in Vertebrate Circulatory Systems
 Blood pressure in left
ventricle changes with
systole and diastole
 Pressures decreases as
blood moves through
system
 Pressure and pulse decrease
in arterioles due to high
resistance
 Velocity of blood highest
in arteries, lowest in
capillaries, and
intermediate in veins
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Figure 8.33
Arteries Act as Pressure Dampeners
 Pressure fluctuations in
arteries are smaller than
those in left ventricle
 Aorta acts as a pressure
reservoir
 Elasticity of vessel wall
 Expands during
systole
 Elastic recoil during
diastole
 Dampens pressure
fluctuations
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Figure 8.34
Mean Arterial Pressure (MAP)
 Average arterial pressure over time
 MAP = 2/3 diastolic pressure + 1/3 systolic pressure
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Table 8.2
Moving Blood Back to the Heart
 Blood in veins is under
low pressure
 Two pumps assist in
moving blood back the
heart
 Skeletal muscle
 Contraction (shortening
and thickening) of
muscle squeezes vein
 Respiratory pumps
 Pressure changes in
thoracic cavity during
ventilation
 Valves in veins assure
unidirectional flow
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Figure 8.35
Veins Act as a Volume Reservoir
 Veins have thin, compliant
walls
 Small increases in blood
pressure lead to large changes
in volume
 In mammals, veins hold more
than 60% of the blood
 Vein volume (and venous
return) controlled by
sympathetic nerves
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Figure 8.36
Regulation of Blood Pressure
 Peripheral resistance influences pressure
 Cardiac output (CO)
 Total peripheral resistance (TPR) to maintain a near
constant mean arterial pressure (MAP)
 Pressure is the primary driving force for blood flow
through organs
 Rearrange the equation: CO = MAP / TPR
 MAP = CO  TPR
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Regulation of Blood Pressure
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Figure 8.37
Baroreceptor Reflex
 Baroreceptors
 Stretch-sensitive mechanoreceptors are in walls of
many major blood vessels
 Especially carotid arteries
and aorta
 Send nerve signals to
medulla oblongata
(cardiovascular control
center)
 Baroreceptor reflex regulates
MAP
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Figure 8.38
Kidneys Help Maintain Blood Volume
 Increases in blood volume
leads to increase in blood
pressure, and vice versa
 Kidneys excrete or retain
water to adjust blood
volume (and pressure)
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Figure 8.39
Net Filtration Pressure (NFP)
 Blood pressure forces fluid out of capillaries
 Starling principle: NFP = (Pcap – Pif) – (pcap – pif)
 NFP = net filtration pressure
 Pcap = hydrostatic pressure of blood in the capillary
 Pif = hydrostatic pressure of interstitial fluid
 pcap = osmotic pressure in the capillary
 pif = osmotic pressure interstitial fluid
 May result in net filtration or net reabsorption
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Net Filtration Pressure (NFP)
NFP = (Pcap – Pif) – (pcap – pif)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 8.40
The Lymphatic System
 Collects excess
filtered fluid and
returns it to circulatory
system
 Lymph nodes filter
lymph to remove
pathogens
 Lymphocytes
 Lymphatic veins and
ducts contain valves to
prevent backflow
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Figure 8.41
Affect of Gravity on Blood Pressure
 Hydrostatic pressure
 Pressure of a column of fluid due to gravity
 DP = r  g  Dh
 DP = pressure difference between two points
 r = density of the fluid
 g = acceleration due to gravity
 Dh = height of the fluid column
 Blood flow may be with or against force of gravity
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Body Position
 Changes in body position can alter blood pressure
and flow
 Changes relative to gravity
 Standing up causes pooling of blood in lower body
  venous return,  in SV,  MAP
 Baroreceptor reflex brings MAP back to normal
  HR and  SV raise MAP
 Orthostatic hypotension
 Low blood pressure upon standing when reflex is too
slow
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Body Position and Blood Pressure
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Figure 8.42 and Figure 8.43
Composition of Blood
p397
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Composition of Blood
 Primarily water, containing
 Dissolved ions and organic solutes
 Blood cells (hemocytes)
 Dissolved proteins
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Blood Proteins
 Invertebrates
 Primarily respiratory pigments
 Vertebrates
 Carrier proteins such as albumin and globulins
 Proteins involved in blood clotting
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Blood Cells (Hemocytes)
 Functions
 Oxygen transport or storage
 Nutrient transport or storage
 Phagocytosis
 Immune defense
 Blood clotting
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 8.44
Red Blood Cells (Erythrocytes)
 Most abundant cells in blood of vertebrates
 Contain high concentrations of respiratory
pigments (such as hemoglobin)
 Major function is storage and transport of oxygen
 Erythrocytes have evolved independently several
times
 Also found in various worms, molluscs, and
echinoderms
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Vertebrate Blood
 Separates into three
main components
when centrifuged
 Plasma
 Erythrocytes
 Other blood cells and
clotting cells
 Hematocrit – Fraction
of blood made up of
erythrocytes
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Figure 8.45
Erythrocytes
 Size of erythrocytes varies among vertebrates
 Smaller in mammals than in fish and amphibians
 Generally round or oval in shape
 Mammalian erythrocytes are biconcave disks
 Increased surface area, facilitating oxygen transfer
 Mammalian erythrocytes lack nucleus,
mitochondria, and ribosomes
 Cannot divide
 Have limited lifespan in circulatory system
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•
•
Size of erythrocytes
Salamander amphiuma
2000 X
Tragulus javanicus
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White Blood Cells (Leukocytes)
 Function in immune
response
 All are nucleated
 Found both in blood and
interstitial fluid
 Some able to move across
capillary walls
 Five major types





Neutrophil
Eosinophil
Basophil
Monocyte / macrophage
Lymphocyte
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Figure 8.46
Blood Cell Formation (Hematopoiesis)
 Location of stem cells
 Adult mammals
 Only in red bone marrow
 Fishes
 Kidney
 Amphibians, reptiles, birds
 Spleen, liver, kidney, bone marrow
 Signaling factors regulate hematopoiesis
 For example, erythropoietin is a hormone released by
the kidney in response to low blood oxygen
 Stimulates formation of erythrocytes in red bone marrow
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Blood Cell Formation (Hematopoiesis)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Figure 8.47