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3.4 The Circulatory System

The Circulatory System
The human circulatory system is made up of the blood, the heart, and
the blood vessels. The function of the circulatory system is to transport
substances around the body. It moves nutrients absorbed from the intestine
to all of the body’s cells. Blood flows through the lungs (part of the
respiratory system) to pick up oxygen and then flows through the body
to deliver it to active cells. Blood also carries wastes from the body tissues
for disposal. It carries carbon dioxide to the lungs, where it is released into
the air. Other waste substances are carried to the kidneys (an organ of the
urinary system), where the substances are filtered out and excreted.
Among the circulatory system’s other vital functions are the regulation of
body temperature and the transport of disease-fighting white blood cells to
areas of the body where there are viruses or bacteria.
circulatory system the organ system that
is made up of the heart, the blood, and the
blood vessels; the system that transports
oxygen and nutrients throughout the body
and carries away wastes
To watch a dissection of the organ
systems of a fish,
dioxide out
Parts of the Circulatory System
The three main parts of the circulatory system are the blood, the
heart, and the blood vessels. The heart pumps the blood through
large blood vessels, called arteries, which branch into smaller
and smaller blood vessels. The smallest blood vessels are called
capillaries. In the capillaries, blood exchanges many substances
with the surrounding tissues (Figure 1). After this exchange, blood
flows into larger blood vessels called veins and eventually returns to
the heart. Let’s now look at these parts in detail.
oxygen in
capillaries in lungs, where
gas exchange takes place
Blood is a type of connective tissue that circulates throughout all
parts of your body. The blood consists of four components (Figure 2):
• Red blood cells are the most plentiful of the body’s blood
cells. These cells make up almost half of the blood’s volume.
Red blood cells contain a protein called hemoglobin, which
allows them to transport oxygen throughout the body.
Hemoglobin makes the cells appear red.
• White blood cells are infection-fighting cells in the blood.
They recognize and destroy invading bacteria and viruses.
White blood cells make up less than 1 % of the volume
of blood. They are the only blood cells to have a nucleus.
• Platelets are tiny cells that help in blood clotting. They also
comprise less than 1 % of the blood.
• Plasma is a protein-rich liquid that carries the blood cells along.
It makes up over half of blood’s volume.
dioxide in
oxygen out
capillaries in body tissues,
where gas exchange takes place
Figure 1 The circulatory system
connects all parts of the body. In this
the oxygenated blood is shown
in red. The deoxygenated blood is
shown in blue. Note that this diagram is
not to scale.
Joel and Sharon Harris
Figure 2 Blood cells
3.4 The Circulatory System
The Heart
Artificial Heart
Dr. Tofy Mussivand, of the Medical
Devices Centre at the University of
Ottawa Heart Institute, researches
and designs artificial hearts. A patient
needing a heart transplant may receive
an artificial heart until a donor heart
becomes available.
The heart is made up of three different types of tissue: cardiac muscle tissue,
nerve tissue, and connective tissue. Cardiac muscle tissue is a special type of
muscle found only in the heart (Figure 3). All of the cardiac muscle tissue
in each part of the heart contracts at the same time. This makes the heart
contract and moves the blood around the body.
Your heart pumps with a regular beat. The frequency of the beat (the
heart rate) changes depending on your physical activity and other factors,
such as stress, temperature, and your general health.
The muscles and nerves are covered by a smooth layer of epithelial tissues.
This covering reduces friction and protects the heart from damage when the
lungs expand and contract. The inner surface of the heart, where the blood
flows, is also lined with smooth epithelial tissue to allow the blood to flow freely.
Any hardening or roughening of this inner lining can lead to health problems.
Blood Vessels
artery a thick-walled blood vessel that
carries blood away from the heart
vein a blood vessel that returns blood to
the heart
capillary a tiny, thin-walled blood vessel
that enables the exchange of gases,
nutrients, and wastes between the blood
and the body tissues
Three types of blood vessels form a network of tubes throughout the body to
transport the blood. These three types of blood vessels are arteries, veins, and
capillaries. Arteries carry blood away from the heart. Because the blood in
the arteries is being pumped away from the heart, it is under greater pressure
than the blood in other blood vessels. The walls of arteries are thicker than
the walls of other blood vessels to withstand this pressure. Veins carry blood
toward the heart. This blood is at lower pressure, so the walls of the veins are
not as thick. Both arteries and veins can vary considerably in size. The largest
are nearest the heart, where just a few blood vessels carry large volumes of
blood. Further from the heart, the blood vessels are much smaller, and there
are more of them, like twigs on a tree. Arteries and veins are linked together
by the capillaries (Figure 4). Capillaries are tiny blood vessels with very thin
walls that allow substances to diffuse between the blood and other body fluids
and tissues. Oxygen and nutrients diffuse from the blood into the surrounding
tissues. Carbon dioxide and other wastes pass from the body tissues into the
blood to be carried away for disposal. Every part of the body is supplied with
blood by a network of capillaries.
Figure 3 In this photo of healthy cardiac tissue, the fibres of cardiac
muscle are stained pink. Their nuclei are purple.
Chapter 3 • Animal Systems
Figure 4 Capillaries can be so narrow that red blood cells can only
pass through one at a time.
SKILLS: Performing, Observing, Communicating
2.D., 3.B.6.
Arteries, veins, and capillaries are all blood vessels, but they
have very different functions. In this activity, you will look at their
structures and see how the structure is related to the function.
1. Use your microscope to examine the slide showing an artery.
Draw a diagram to illustrate what you see.
Equipment and Materials: microscope; lens paper; prepared
slides of cross-sections through arteries, veins, and capillaries
A. How are the different functions of the three blood vessels
reflected in their structures? T/I
2. Repeat Step 1 with the other two slides.
Diseases and Disorders of the
Circulatory System
There are many conditions that affect the function of the circulatory system.
There are over a dozen types of heart disease alone that can affect people
of all ages and all levels of fitness. The most common heart problems is
coronary artery disease, which can lead to heart attack.
Coronary Artery Disease
Your heart is a hard-working organ, and the cardiac muscle tissue needs
a steady supply of oxygen and nutrients. Coronary arteries are the blood
vessels that provide blood to the heart muscle tissue itself. These arteries can
become partially blocked with plaque—a deposit made of fat, cholesterol,
calcium, and other substances that normally circulate in the blood. This
plaque buildup can be caused by inherited genetic information or by poor
lifestyle choices, such as a high-fat diet, smoking, and lack of exercise.
Symptoms of coronary artery disease include tiredness, dizziness, and
pain or a burning sensation in the chest or arms. The problem can be
diagnosed with the aid of a special X-ray called an angiogram, in which a
fluorescent dye is injected into the bloodstream. This dye shows up on the
X-ray image (Figure 5).
Describing Observations
Use a thesaurus to find words
that describe your observations as
specifically and accurately as possible.
Use words that help readers visualize
your observations clearly. By using
concrete nouns, adjectives, verbs, and
adverbs, your description will give
readers a clear picture of what you saw.
Figure 5 During an angiogram, a
fluorescent dye is injected into the
artery and X-ray scans are taken. This
X-ray image has been colourized by a
computer. A white rectangle highlights
the blockage in the artery in a patient’s
3.4 The Circulatory System
Heart Attack
Blood Clotting
It is important that blood forms clots
when the blood vessels are damaged
by a cut or scrape. Some people
have disorders that cause the blood
to clot too easily, causing blockages,
or not quickly enough, so they bleed
uncontrollably. Both problems can be
Coronary arteries can become completely blocked, either with plaque or
with a blood clot. When this happens, the heart muscle cells no longer
receive the oxygen and nutrients they need to function. The heart stops
pumping, and the heart tissue starts to die.
General symptoms of a possible heart attack include
• chest pain or pressure
• shortness of breath
• nausea
• anxiety
• upper body pain
• abdominal or stomach pain
• sweating
• dizziness
• unusual fatigue
electrocardiogram (ECG) a diagnostic
test that measures the electrical activity
pattern of the heart through its beat cycle
Figure 6 A patient having an
electrocardiogram. The blue and white
circles are electrodes placed on the
skin. These electrodes detect electrical
The actual symptoms of a heart attack can vary widely between men
and women and from person to person, but any suspicion of a heart attack
requires immediate medical attention. A heart attack can be diagnosed
with a blood test and an electrocardiogram. The blood test identifies
certain proteins that are present only when cardiac muscle tissue dies. The
electrocardiogram (or ECG) measures the electrical signals created by the
heart as it beats (Figure 6). The electrical signals from damaged heart muscle
tissue are not the same as those from healthy heart muscle.
Chapter 3 • Animal Systems
SKILLS: Researching, Analyzing the Issue, Communicating
The circulatory system is vitally important to our health.
Blockages and other problems can occur in blood vessels in
many parts of the body.
1. Chose one specific disease or disorder of the circulatory
system to research, such as coronary artery disease, heart
attack, stroke, deep vein thrombosis, or anemia.
2. Research your chosen disease. Find out the causes,
symptoms, diagnostic technologies, treatment, and long-term
effects. If you have time, you could also look at the social and
economic impacts of your chosen disease.
4.A., 4.B.
A. Think about how life would change for someone who
discovers that he or she has this problem. Write a list of
probable life changes. T/I A
B. Summarize your findings in an illustrated presentation or
as a short dramatic performance. T/I C
C. As a class, discuss whether there are any drawbacks to the
use of medical technologies. How expensive are they? Are
they readily available to everybody? C A
UNIT TASK Bookmark
How could you use information about the symptoms of heart disease as you work on the
Unit Task on page 156?
• The circulatory system is an organ system made
up of the blood, the heart, and the blood vessels.
• Heart disease is a group of conditions that affect
the function of the heart.
• The function of the circulatory system is to move
nutrients and gases to all of the cells of the body
and to carry away wastes through the bloodstream.
• Angiograms and electrocardiograms are two
medical technologies that are used to help
diagnose abnormalities in the circulatory system.
1. Describe the function of the circulatory system. K/U
2. Name at least four substances that are carried by the
circulatory system. K/U
3. Explain how the circulatory system interacts with the
digestive system. K/U
4. How does an angiogram differ from a regular X-ray
scan? K/U
5. Figure 7 shows cross-sections of three different blood
vessels. Name each one and describe how its structure
matches its function. K/U
6. Create a table that lists the main parts of the circulatory
system and the tissue types in each part. K/U C
7. (a) Create a pie chart to illustrate the volumes of the
various components of blood.
(b) What challenges did you face when creating your
chart? K/U C
8. How is cardiac muscle different from the smooth muscle
that surrounds the digestive tract? K/U
9. Name and briefly describe two diseases or disorders
of the circulatory system. K/U
Figure 7
3.4 The Circulatory System