The Circulatory System
The Nature of Blood Circulation
 A circulatory system distributes materials
throughout the vertebrate body (and some
invertebrates)
 Uses a transport medium called blood.
 A heart is a muscular organ that pumps the
transport medium (blood) through vessels.
 Blood and interstitial fluid (fluid between cells)
make up the body’s internal environment
Two Kinds of Circulatory Systems
 Open circulatory system (arthropods, mollusks)
• Blood moves through hearts and large vessels, but
also mixes with interstitial fluid
 Closed circulatory system (annelids, vertebrates)
• Blood remains inside heart and blood vessels
• Materials diffuse between blood and interstitial fluid
at capillaries
Open Circulatory Systems
aorta
heart
pump
spaces or
cavities
in body
tissues
A In a grasshopper’s open system, a heart (not like yours) pumps
blood through a vessel, a type of aorta. From there, blood moves into
tissue spaces, mingles with interstitial fluid, then reenters the heart at
openings in the heart wall.
Fig. 37-2a, p. 638
Closed Circulatory Systems
dorsal blood vessel
pump
largediameter
blood
vessels
capillary bed (many
small vessels that serve
as a diffusion zone)
large-diameter
blood vessels
two of five
hearts
ventral blood gut cavity
vessels
B The closed system of an earthworm confines
blood inside pairs of muscular hearts near the head
end and inside many blood vessels.
Fig. 37-2b, p. 638
Evolution of Circulation in Vertebrates
 Fishes
• Heart with two chambers
• Single circuit of circulation
 Amphibians
• Heart with three chambers
• Two partially separated circuits
 Birds and mammals
• Heart with four chambers
• Two fully separate circuits
Single Circuit of Circulation
capillary beds
of gills
heart
A In fishes, the heart has two
chambers: one atrium and one
ventricle. Blood flows through one
circuit. It picks up oxygen in the
capillary beds of the gills, and
delivers it to capillary beds in all
body tissues. Oxygen-poor blood
then returns to the heart.
rest of body
Fig. 37-3a, p. 639
Two Partially Circuits of Circulation
lungs
right
atrium
left
atrium
ventricle
rest of body
B In amphibians, the heart has
three chambers: two atria and one
ventricle. Blood flows along two
partially separated circuits. The
force of one contraction pumps
blood from the heart to the lungs
and back. The force of a second
contraction pumps blood from the
heart to all body tissues and back
to the heart.
Fig. 37-3b, p. 639
Circulation in Birds and Mammals
 The four-chambered heart has two separate
halves, each with an atrium and a ventricle
 Each half pumps blood in a separate circuit
• Pulmonary circuit: Blood flows from right half of
heart, to lungs (gains oxygen), to left half of heart
• Systemic circuit: Blood flows from left half of
heart, to body (loses oxygen), to right half of heart
Two Fully Separate Circuits of Circulation
lungs
right
atrium
right ventricle
left
atrium
left ventricle
C In birds and mammals, the heart
has four chambers: two atria and two
ventricles. The blood flows through
two fully separated circuits. In one
circuit, blood flows from the heart to
the lungs and back. In the second
circuit, blood flows from the heart to
all body tissues and back.
rest of body
Fig. 37-3c, p. 639
Analogy of Slowing Blood in Capillaries
lake
river in
river out
1 2 3
1 2 3
123
D Why flow slows in capillaries.
Picture a volume of water in two
fast rivers flowing into and out
of a lake. The flow rate is
constant, with an identical
volume moving from points 1 to
3 in the same interval. However,
flow velocity decreases in the
lake. Why? The volume spreads
out through a larger crosssectional area and flows
forward a shorter distance
during the specified interval.
Fig. 37-3d, p. 639
Overview of Circulatory Systems
 Fill in the blank.
 Many animals have either an ________ or a
________ circulatory system that transports
substances to and from all body tissues.
 All vertebrates have a _______ circulatory
system, in which blood is
_______________________________.
Overview of Circulatory Systems
 Many animals have either an open or a closed
circulatory system that transports substances to
and from all body tissues
 All vertebrates have a closed circulatory system,
in which blood is always contained within the
heart or blood vessels
Characteristics of Blood
 Blood, considering it is made of cells, can be
called a large interconnect tissue.
 Blood consists mainly of plasma, a protein-rich
fluid that carries wastes, gases and nutrients.
 Blood cells and platelets form in bone marrow
and are transported in plasma.
• Platelets are fragments of megakaryocytes,
active in clotting.
Blood Cells
 Red blood cells (erythrocytes)
• Contain hemoglobin that carries oxygen from
lungs to tissues
• Quantified in cell count
 White blood cells (leukocytes)
• Defend the body from pathogens
• Neutrophils, basophils, eosinophils, monocytes,
and lymphocytes (B and T cells)
Components of Human Blood
Components
Amounts
Main Functions
Plasma Portion (50-60% of total blood volume)
1. Water
91-92% of total
plasma volume
2. Plasma proteins (albumins,
globulins, fibrinogen, etc. 7-8%
3. Ions, sugars, lipids, amino
acids, hormones, vitamins, 1-2%
dissolved gases, etc.
Solvent
Defense, clotting, lipid
transport, extracellular
fluid volume controls
Nutrition, defense,
respiration, extracellular
fluid volume controls,
cell communication, etc.
Cellular Portion (40-50% of total blood volume; numbers per microliter)
Oxygen, carbon
1. Red blood cells
4,600,000-5,400,000 dioxide transport to
and from lungs
2. White blood cells:
Neutophils
Lymphoctyes
Monocytes (macrophages)
Eosinophils
Basophils
3,000-6,750
1,000-2,700
150-720
100-380
25-90
Fast-acting phagocytosis
Immune responses
Phagocytosis
Killing parasitic worms
Anti-inflammatory secretions
3. Platelets
250,000-300,000
Red
Roles in blood clotting blood cell
White
blood cell
platelet
Stepped Art
Fig. 37-4, p. 640
Cellular Components of Human Blood
stem cell in bone marrow
myeloid stem cell
red blood cell
precursor
granulocyte
precursor
lymphoid stem cell
monocyte
precursor
megakaryocytes
platelets
red blood cells
(erythrocytes)
neutrophils
basophils monocytes
T lymphocytes
eosinophils
(immature
(mature in
phagocytes)
thymus)
B lymphocytes
(mature in bone
marrow)
Fig. 37-5, p. 641
Hemostasis
 Hemostasis = Heme (blood) stasis (balance)
• Keeping blood pressure/volume stable.
 How do we stop bleeding?
 Initiated by a hormone cascade when an injury
is sustained and blood vessels are broken.
 Hemostasis is a three-phase process that stops
blood loss, constructs a framework for repairs
• Damaged vessel constricts
• Platelets accumulate
• Cascading enzyme reactions involving plasma
proteins cause clot formation
Three-Phase Process of Hemostasis
Stimulus
A blood vessel is damaged.
Phase 1 response
A vascular spasm constricts the vessel.
Phase 2 response
Platelets stick together plugging the site.
Phase 3 response
Clot formation starts:
1. Enzyme cascade results in activation
of Factor X.
2. Factor X converts prothrombin in
plasma to thrombin
3. Thrombin converts fibrinogen, a
plasma protein, to fibrin threads.
4. Fibrin forms a net that entangles
cells and platelets, forming a clot.
Stepped Art
Fig. 37-6, p. 642
Blood Typing
 Blood type
• Genetically determined differences in molecules
on the surface of red blood cells
 Agglutination
• Clumping of foreign cells by plasma proteins
• When blood of incompatible types mixes, the
immune system attacks the unfamiliar molecules
Agglutination
Light micrographs showing (a) an absence of
agglutination in a mixture of two different yet compatible
blood types and (b) agglutination in a mixture of
incompatible types.
ABO Blood Typing
 Blood type O is a universal donor; blood type AB
can receive blood from any donor
Mixing
ABO
Blood
Types
O
Blood Type of Donor
A
B
AB
Blood Type of Recipient
O
A
B
AB
Fig. 37-8, p. 643
Rh Blood Typing
 An Rh- mother may develop Rh+ antibodies if
blood from an Rh+ child enters her bloodstream
during childbirth
 These antibodies may attack the red blood cells
of the next Rh+ fetus
Rh Complications of Pregnancy
How Rh differences can complicate pregnancy.
Blood Composition and Function
 Fill in the blanks.
 Vertebrate blood is a fluid connective ________.
 It consists of _______, ________, ________,
and _________ (the transport medium)
 _____ _______ cells function in gas exchange;
_____ _______ cells defend tissues, and
_________ function in clotting
Blood Composition and Function
 Vertebrate blood is a fluid connective tissue
 It consists of red blood cells, white blood cells,
platelets, and plasma (the transport medium)
 Red blood cells function in gas exchange; white
blood cells defend tissues, and platelets function
in clotting
Human Cardiovascular System
 The term “cardiovascular” comes from the Greek
kardia (for heart) and Latin vasculum (vessel)
 In a cardiovascular circuit, blood flows from the
heart through arteries, arterioles, capillaries,
venules, veins, and back to the heart.
Two Circuits of
the Human Cardiovascular System
 Pulmonary circuit
• Oxygen-poor blood flows from the heart, through
a pair of lungs, then back to the heart
• Blood takes up oxygen in the lungs
 Systemic circuit
• Oxygenated blood flows from the heart (through
the aorta) into capillary beds where it gives up O2
and takes up CO2, then flows back to the heart
of the Human Cardiovascular System
right pulmonary artery
capillary bed
of right lung
Accessing the
lungs to rid
blood stream of
excess CO2 & to
replenish O2
pulmonary
trunk
left pulmonary artery
capillary bed
of left lung
to systemic circuit
from
systemic
circuit
pulmonary
veins
heart
Blood vessels carrying oxygenated blood
are shown in red. Those that hold oxygenpoor blood are color-coded blue.
Fig. 37-10a, p. 644
Systemic Circuit
of the Human
Cardiovascular
System
Accessing the
rest of the body
to deliver O2
& to retrieve CO2
Pulmonary and systemic
circuits of the human
cardiovascular system. Blood
vessels carrying oxygenated
blood are shown in red. Those
that hold oxygen-poor blood
are color-coded blue.
(pulmonary
vessels to and
from thoracic
cavity)
capillary beds of head,
upper extremities
to pulmonary aorta
circuit
from
pulmonary
circuit
heart
(diaphragm, the
muscular partition
between thoracic
and abdominal
cavities)
capillary beds of other
organs in thoracic cavity
capillary bed of liver
capillary beds of intestines
B
Systemic Circuit for
Blood Flow
capillary beds of other abdominal
organs and lower extremities
The Pulmonary Circuit
Does?
The Systemic Circuit
Does?
Blue = deoxygenated
Red = oxygenated
food, water intake
oxygen intake
Digestive System
nutrients,
water, salts
The Circulatory System
and Homeostasis
Respiratory System
oxygen
elimination of
carbon dioxide
carbon dioxide
Circulatory System
Urinary System
water, solutes
elimination of
food residues
Functional links
between the circulatory
rapid transport to system and other organ elimination of
and from all living systems with major
excess water, salts,
cells
roles in maintaining the wastes
internal environment.
Fig. 37-12, p. 645
The Human Heart
 A sac of connective tissue (pericardium)
surrounds the heart muscle (myocardium)
 Endothelium lines heart chambers and blood
vessels
 Heart valves keep blood moving in one direction
• AV valves separate atria and ventricles
• Semilunar valves separate ventricles and arteries
The Human Heart
right lung
left lung
1
B The heart is
located between
the lungs in the
thoracic cavity.
2
ribs
1–8
3
4
5
6
7
8
pericardium
diaphragm
Fig. 37-13b, p. 646
The Human Heart
superior vena cava
(flow from head, arms)
arch of aorta
trunk of pulmonary
arteries (to lungs)
right semilunar valve
(shown closed) to
pulmonary trunk
left semilunar valve
(closed) to aorta
right pulmonary
veins (from lungs)
left pulmonary veins
(from lungs)
right atrium
left atrium
right AV valve
(opened)
left AV valve
(opened)
right ventricle
left ventricle
(muscles that
prevent valve
from everting)
endothelium
and underlying
connective tissue
inferior vena cava
(from trunk, legs)
myocardium
septum (partition between
heart’s two halves)
inner layer
of pericardium
heart’s apex
Fig. 37-13a, p. 646
The Human Heart
C Outer appearance.
Pads of fat on the
heart’s surface are
normal.
Fig. 37-13c, p. 646
The Cardiac Cycle
 Cardiac cycle: Heart muscle alternates between
diastole (relaxation) and systole (contraction)
•
•
•
•
Blood collects in atria
AV valves open, blood flows into ventricles
Contraction of ventricles drives blood circulation
Ventricles contract with a wringing motion from
bottom to top
The Cardiac Cycle
A Atria fill. Fluid
pressure opens
the AV valves,
blood flows into
the ventricles.
B Next, atria
contract. As
fluid pressure
rises in the
ventricles, AV
valves close.
D Ventricles
relax. Semilunar
valves close as
atria begin
filling for the
next cardiac
cycle.
C Ventricles
contract.
Semilunar
valves open.
Blood flows
into aorta and
pulmonary
artery.
Stepped Art
Fig. 37-14, p. 647
Cardiac Muscle
 Cardiac muscle cells are striated (divided into
sarcomeres) and have many mitochondria
 Cells attach end to end at intercalated discs
 Neighboring cells communicate through gap
junctions that conduct waves of excitation
Cardiac Muscle Cells and Gap Junctions
intercalated disk
a branching cardiac muscle cell
(part of one cardiac muscle fiber)
b Part of a gap junction across the
plasma membrane of a cardiac muscle
cell. The junctions connect cytoplasm of
adjoining cells and allow electrical signals
that stimulate contraction to spread
swiftly between them.
Fig. 37-15, p. 647
How the Heart Beats
 Cardiac pacemaker (SA node)
• A clump of noncontracting cells in the right
atrium’s wall spontaneously fires action potentials
about 70 times per minute
 Cardiac conduction system
• Signal spreads from SA node to AV node and
junctional fibers in the septum, so heart contracts
in a coordinated fashion
The Cardiac Conduction System
SA node
(cardiac pacemaker)
AV node
(the only point of
electrical contact
between atria and
ventricles)
junctional fibers
branchings of
junctional fibers
(carry electrical
signals through the
ventricles)
Fig. 37-16, p. 647
The Human Heart and Two Flow Circuits
 Fill in the blanks
 The ______-chambered human heart pumps
blood through _____ separate circuits of blood
vessels
 One circuit extends through _____________,
the other through _______ tissue only.
 Both circuits loop back to the __________,
which keeps blood flowing through the _______
circuits.
The Human Heart and Two Flow Circuits
 The four-chambered human heart pumps blood
through two separate circuits of blood vessels
 One circuit extends through all body regions, the
other through lung tissue only.
 Both circuits loop back to the heart, which keeps
blood flowing through the two circuits.
Part II
 Pressure, Transport,
and Flow Distribution
Major Blood Vessels
of the Human Cardiovascular System
Jugular Veins
Carotid Arteries
Ascending Aorta
Superior Vena Cava
Pulmonary Arteries
Pulmonary Veins
Coronary Arteries
Hepatic Vein
Brachial Artery
Renal Vein
Renal Artery
Inferior Vena Cava
Abdominal Aorta
Iliac Veins
Iliac Arteries
Femoral Vein
Femoral Artery
Fig. 37-11, p. 645
Pressure, Transport,
and Flow Distribution
 Contracting ventricles put pressure on the blood,
forcing it through a series of vessels
•
•
•
•
•
Arteries carry blood from ventricles to arterioles
Arterioles control blood distribution to capillaries
Capillaries exchange substances
Venules collect blood from capillaries
Veins deliver blood back to heart
Human Blood Vessels
outer
coat
smooth
muscle
basement
membrane
endothelium
Artery
elastic tissue
elastic tissue
Fig. 37-17a, p. 648
Human Blood Vessels
outer
coat
smooth muscle rings basement
over elastic tissue
membrane endothelium
Arteriole
Fig. 37-17b, p. 648
Human Blood Vessels
basement
membrane
endothelium
Capillary
(venules have a
similar structure)
Fig. 37-17c, p. 648
Human Blood Vessels
outer
coat
smooth muscle,
elastic fibers
basement
membrane
endothelium
Vein
valve
Fig. 37-17d, p. 648
Blood Pressure
 Blood pressure
• The pressure exerted by blood on the walls of
blood vessels
• Highest in arteries, then declines through circuit
• Rate of blood flow depends on the difference in
blood pressure between two points, and
resistance to flow
arteries
capillaries
veins
Blood Pressure
in the Systolic
Circuit: Plot of fluid
pressure for a volume of
blood as it flows through
the systemic circuit.
Systolic pressure occurs
when ventricles contract,
diastolic when ventricles
are relaxed.
arterioles
venules
Fig. 37-18, p. 648
Blood Flow
 Thick, elastic arteries smooth out variations in
blood pressure during the cardiac cycle
 Arterioles respond to signals from the autonomic
and nervous systems, and to chemical signals,
to direct blood flow to different parts of the body
100%
Distribution
of Cardiac
Output
in a Resting
Person
Figure It Out: What
percentage of the
brain’s blood supply
arrives from the
heart’s right half?
Answer: None
lungs
heart’s right half
liver
digestive tract
kidneys
skeletal muscle
brain
skin
bone
cardiac muscle
all other regions
heart’s left half
6%
21%
20%
15%
13%
9%
5%
3%
8%
Fig. 37-19, p. 649
Controlling Blood Pressure
 Blood pressure depends on total blood volume,
how much blood the ventricles pump (cardiac
output), and whether arterioles are constricted or
dilated
 Receptors in the aorta and carotid arteries
monitor blood pressure and send signals to the
medulla, which regulates cardiac output and
arteriole diameter
Measuring Blood Pressure
Diffusion at Capillaries,
Then Back to the Heart
 Capillary
• A cylinder of endothelial cells, one cell thick
• Capillary beds are diffusion zones, where blood
exchanges substances with interstitial fluid
• Hydrostatic pressure moves materials out
(ultrafiltration)
• Osmotic pressure moves water in (capillary
reabsorption)
Fluid Movement at a Capillary Bed
blood to
venule
high pressure
causes outward flow
blood from
arteriole
Fluid movement at a capillary bed. Fluid crosses a capillary wall by way of
ultrafiltration and reabsorption. (a) At the capillary’s arteriole end, a difference
between blood pressure and interstitial fluid pressure forces out plasma, but few
plasma proteins, through clefts between endothelial cells of the capillary wall.
Ultrafiltration is the outward flow of fluid across the capillary wall as a result of
hydrostatic pressure. (b) Reabsorption is the osmotic movement of some
interstitial fluid into the capillary. It happens when the water concentration between
interstitial fluid and the plasma differs. Plasma, with its dissolved proteins, has a
greater solute concentration and therefore a lower water concentration.
Reabsorption near the end of a capillary bed tends to balance ultrafiltration at the
start of it. Normally, there is only a small net filtration of fluid, which vessels of the
lymphatic system return to blood (Section 37.10).
cells of
tissue
inward-directed
osmotic movement
B
A
Venous Pressure
 Venules deliver blood from capillaries to veins
 Veins deliver blood to the heart
• Large-diameter, blood volume reservoirs
• Valves help prevent backflow
• Amount of blood in veins varies with activity level
Venous Valve
Action
Venous valve action. (a)
Valves in medium-sized
veins prevent the backflow of
blood. Adjacent skeletal
muscles helps raise fluid
pressure inside a vein. (b)
These muscles bulge into a
vein as they contract.
Pressure inside the vein
rises and helps keeps blood
flowing forward. (c) When
muscles relax, the pressure
that they exerted on the vein
is lifted. Venous valves shut
and cut off backflow.
venous valve
Fig. 37-22a, p. 651
blood flow to heart
valve
open
valve
closed
valve
closed
valve
closed
Key Concepts
Blood Vessel Structure and Function
 The heart pumps blood rhythmically, on its own
 Adjustments at arterioles regulate how blood
volume is distributed among tissues
 Exchange of gases, wastes, and nutrients
between the blood and tissues takes place at
capillaries
Blood and Cardiovascular Disorders
 Red blood cell disorders
• Anemias, beta-thalassemias, polycythemia
 White blood cell disorders
• Infectious mononucleosis, leukemias, lymphomas
 Clotting disorders
• Hemophilia, thrombus, embolus
Blood and Cardiovascular Disorders
 Atherosclerosis
• Buildup of lipids in the arterial wall that narrows
the lumen, may rupture and trigger heart attack
wall of artery,
cross-section
unobstructed
lumen of
a normal
artery
Fig. 37-23a, p. 652
atherosclerotic
plaque
blood clot
sticking to
plaque
narrowed
lumen
Fig. 37-23b, p. 652
Clogged Coronary Arteries
coronary
artery
The photo shows coronary arteries and other blood vessels that service the
heart. Resins were injected into them. Then the cardiac tissues were dissolved
to make an accurate, three-dimensional corrosion cast.
Fig. 37-24a, p. 653
The sketch shows two
coronary bypasses
(color-coded green),
which extend from the
aorta past two clogged
parts of the coronary
arteries.
aorta
coronary
artery
blockage
location of a shunt
made of a section
taken from one of
the patient’s other
blood vessels
Fig. 37-24b, p. 653
Blood and Cardiovascular Disorders
 Hypertension – a silent killer
• Chronic blood pressure above 140/90
 High blood pressure and atherosclerosis
increase the risk of heart attack and stroke
one normal
heartbeat
Blood and
Cardiovascular
Disorders
 Arrhythmias –
abnormal heart
rhythms
• EKGs record
electrical
activity of
cardiac cycle
0 0.2 0.4 0.6 0.8
a time (seconds)
bradycardia
(here, 46
beats per
minute)
b
tachycardia
(here, 136
beats per
minute)
c
ventricular
fibrillation
d
Fig. 37-25, p. 653
Risk Factors
 Cardiovascular disorders are the leading cause
of death in the United States
 Risk factors
• Tobacco smoking, family history, hypertension,
high cholesterol, diabetes mellitus, obesity, age,
physical inactivity, gender
Key Concepts
When the System Breaks Down
 Cardiovascular problems include clogged blood
vessels or abnormal heart rhythms
 Some problems have a genetic basis; most are
related to age or life-style