Download Introduction to the Cardiovascular System

Introduction to the
Cardiovascular System
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Printed: October 7, 2014
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C HAPTER
Chapter 1. Introduction to the Cardiovascular System
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Introduction to the
Cardiovascular System
Lesson Objectives
•
•
•
•
•
Identify the main structures of the cardiovascular system.
Identify three types of blood vessels.
Describe the differences between the pulmonary and the systemic circulations.
Identify the main structures of the lymphatic system.
Outline how the cardiovascular and the lymphatic systems work together.
Check Your Understanding
• What is an organ system?
• What are the three types of muscles found in the human body?
Vocabulary
•
•
•
•
•
•
•
•
arteries
blood
capillaries
lymphatic system
plasma
pulmonary circulation
systemic circulation
veins
Functions of the Cardiovascular System
Your cardiovascular system has many jobs. It acts as a message delivery service, a pump, a heating system, and
a protector of the body against diseases. Every cell in your body depends on your cardiovascular system. In this
chapter, you will learn how your cardiovascular system works and how it helps to maintain homeostasis.
The cardiovascular system shown in Figure 1.1 is the organ system that is made up of the heart, the blood vessels,
and the blood. It moves nutrients, hormones, gases (such as oxygen) and wastes (such as carbon dioxide) to and
from your cells. It also helps to keep you warm by moving warm blood around your body. To do these tasks, your
cardiovascular system works with other organ systems, such as the respiratory, endocrine, and nervous systems.
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FIGURE 1.1
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The cardiovascular system moves nutrients and other substances throughout the body.
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Chapter 1. Introduction to the Cardiovascular System
The Movement of Gases
The movement of gases, especially oxygen and carbon dioxide, is one of the most important jobs of the cardiovascular system. But the cardiovascular system cannot do this alone. It must work with other organ systems, especially
the respiratory system, to move these gases throughout your body.
Oxygen is needed by every cell in your body. You breathe in oxygen and breathe out carbon dioxide through your
respiratory system. Once oxygen enters your lungs, it must enter your blood stream in order to move around your
body. Oxygen is moved in your blood by attaching to a protein called hemoglobin. The oxygen moves from the
blood into the tissues, while carbon dioxide travels in the opposite direction. Carbon dioxide is transported back to
the lungs, where it moves out of the blood and into your lungs for release from your body.
Parts of the Cardiovascular System
Your heart pushes the blood around your body through the blood vessels. The heart, shown in Figure 1.2, is made
of cardiac muscle. The heart is connected to many blood vessels that bring blood all around the body. The cardiac
muscle contracts and pumps blood through the blood vessels.
FIGURE 1.2
Blood is collected in the heart and
pumped out to the lungs, where it releases carbon dioxide and picks up oxygen before it is pumped to the rest of the
body.
Blood Vessels
The job of the blood vessels is to move the blood around the body. There are three main types of blood vessels in
the body.
1. Arteries are blood vessels that carry blood away from the heart. Arteries have thick walls that have a layer
of smooth muscle, as shown in Figure 1.3. Arteries usually carry oxygen-rich blood around the body. The
blood that is in arteries is under pressure. The contractions of the heart muscle causes blood to push against
the walls of the arteries. This "push" is referred to as blood pressure. Blood pressure is highest in the arteries
and decreases as the blood moves into smaller blood vessels. Thick walls help prevent arteries from bursting
under the pressure of blood.
2. Veins are blood vessels that carry blood back to the heart. Veins have thinner walls than arteries do, as you can
see in Figure 1.4. The blood in veins is not under pressure. Veins have valves that stop blood from moving
backward. Blood is moved forward in veins when the skeletal muscles squeeze the veins. Blood that is carried
by veins is usually low in oxygen. The only veins that carry oxygen-rich blood are called the pulmonary veins,
which carry blood to the heart from the lungs.
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FIGURE 1.3
Arteries are thick-walled vessels with many layers, including a layer of
smooth muscle.
FIGURE 1.4
The walls of veins are not as thick as artery walls; veins have valves that
stop blood from flowing backward.
3. Capillaries these are the tiniest blood vessels in the body. Every cell in the body needs oxygen, but arteries
are too large to bring oxygen and nutrients to single cells. Further from the heart, arteries form capillaries. The
walls of capillaries are only as thick as a single layer of cells. Capillaries connect arteries and veins together,
as shown in Figure 1.5. Capillaries also send water, oxygen and other substances to body cells, while they
collect carbon dioxide and other wastes from cells and tissues. Capillaries are so narrow that blood cells must
move in single file through them. A capillary bed is the network of capillaries that supply an organ with blood.
The more active a tissue or organ is, the more capillaries it needs to get nutrients and oxygen.
FIGURE 1.5
Capillaries connect arteries and veins.
Blood
Blood is a body fluid that is a type of connective tissue. Blood is made of blood cells, and a liquid called plasma.
The main types of cells found in blood are red blood cells and white blood cells.
• Red blood cells carry oxygen. Oxygen-rich blood is bright red and oxygen-poor blood is dark red.
• White blood cells fight against infection and disease.
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Chapter 1. Introduction to the Cardiovascular System
The cardiovascular system of humans is "closed." That means the blood never leaves the blood vessels inside of the
body Other organisms have blood vessels that interact with the environment.
Two Blood Circulation Systems
The blood is pumped around in two large “loops” within the body. One loop moves blood around the body - to the
head, limbs, and internal organs. The other loop moves blood to and from the lungs where carbon dioxide is released
and oxygen is picked up by the blood. A simple version of these two “loops” is shown in Figure 1.6.
Systemic circulation is the part of the cardiovascular system that carries oxygen-rich blood away from the heart, to
the body, and returns oxygen-poor blood back to the heart. Pulmonary circulation is the part of the cardiovascular
system that carries oxygen-poor blood away from the heart to the lungs, and returns oxygen-rich blood back to the
heart.
FIGURE 1.6
The double circulatory system. Trace the
systemic circulation. Where is the path of
pulmonary circulation?
The Lymphatic System
The lymphatic system is a network of vessels and tissues that carry a clear fluid called lymph. The lymphatic
system, shown in Figure 1.7 spreads all around the body. Lymph vessels are tube-shaped, just like blood vessels.
The lymphatic system works with the cardiovascular system to return body fluids to the blood. The lymphatic system
and the cardiovascular system are often called the body’s two "circulatory systems."
Role of the Lymphatic System in Circulation
You may think that your blood vessels have thick walls without any leaks, but it’s not true! Blood vessels can leak
just like any other pipe. The lymphatic system makes sure leaked blood returns back to the bloodstream.
When a small amount of fluid leaks out from the blood vessels, it collects in the spaces between cells and tissues.
Some of the fluid returns to the cardiovascular system, and the rest is collected by the lymph vessels of the lymphatic
system, which are shown in Figure 1.8. The fluid that collects in the lymph vessels is called lymph. The lymphatic
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FIGURE 1.7
The lymphatic system helps return fluid that leaks from the blood vessels
back to the cardiovascular system.
system then returns the lymph to the cardiovascular system. Unlike the cardiovascular system, the lymphatic system
is not closed and has no central pump (or heart). Lymph moves slowly in lymph vessels. It is moved along in the
lymph vessels by the squeezing action of smooth muscles and skeletal muscles.
FIGURE 1.8
Lymph capillaries collect fluid that leaks
out from blood capillaries.
Role of the Lymphatic System in the Body’s Defenses
The lymphatic system also plays an important role in the immune system. The lymphatic system makes white blood
cells that protect the body from diseases.
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Chapter 1. Introduction to the Cardiovascular System
Organs of the Lymphatic System
Along with the lymph vessels, lymph ducts, and lymph nodes, the lymphatic system also includes many organs. The
tonsils, thymus, and spleen, which are shown in Figure 1.7, also help prevent diseases. Many of these organs are
also part of the immune system.
Tonsils
If you open your mouth and look at your throat in a mirror, you may see some lumps in the back of your throat.
These are your tonsils. Tonsils are areas of lymphatic tissue on either side of the throat Figure 1.9. There are also
tonsils in the nasal cavity and behind the tongue. Like other organs of the lymphatic system, the tonsils are also part
of the immune system. The immune system helps protect the body against infection. The tonsils are believed to help
fight off nose and throat, and other upper respiratory tract infections such as colds. Tonsillitis is an infection of the
tonsils that can cause a sore throat and fever.
FIGURE 1.9
This illustration shows the tonsils in the
back of the throat, but there are also
tonsils in the nasal cavity and behind the
tongue.
Bone Marrow
Bone marrow is the tissue found in the middle of bones. The marrow in the large bones of adults makes new blood
cells, like white blood cells, called T-cells. Other white blood cells, called B-cells, are also created in the bone
marrow.
Thymus
The thymus is found in the upper chest. Chemicals made by the thymus help produce cells that fight infection.
White blood cells called lymphocytes move from the bone marrow to the thymus to finish growing. The thymus
grows to its largest size near puberty, and gets smaller as a person ages. If a person’s thymus is surgically removed
or damaged by disease while they are young, the person will be more prone to infection.
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Spleen
The spleen is in the abdomen, as shown in Figure 1.10. In an area of the spleen called red pulp, materials are
filtered from the blood, including old and dead red blood cells. The spleen also makes red blood cells. Areas called
white pulp help fight infections by making white blood cells. If a person’s spleen is surgically removed, or does
not work properly, the person is at risk for certain infections. You can learn more about the roles of the lymphatic
system and white blood cells in the Diseases and the Body’s Defenses chapter.
FIGURE 1.10
In the spleen, the white pulp makes white
blood cells, while the red pulp acts like a
filter and removes dead and dying cells
from the blood.
Lesson Summary
• Table 1.1 summarizes the structures and functions of the cardiovascular and lymphatic systems.
TABLE 1.1: Structures and Functions of the Cardiovascular and Lymphatic Systems
System
Lymphatic
Structure (organs and tissues)
Lymph vessels
Lymph nodes
Spleen, tonsils, and adenoids
Thymus
Cardiovascular
Blood vessels
Blood
Heart
Function
Transport fluid (lymph) from between body cells back to blood
Trap invading diseases and cells
with cancer
Trap invading diseases
where white blood cell (lymphocytes) grow larger
Transport blood around the body
Moves oxygen and nutrients; also
carries white blood cells to sites of
infection and inflammation
Pumps blood around the body
• The cardiovascular system includes the heart, the blood vessels, and the blood.
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Chapter 1. Introduction to the Cardiovascular System
• There are three main types of blood vessels in the body: arteries, veins, and capillaries.
• Systemic circulation is the part of the cardiovascular system that carries oxygen-rich blood away from the
heart, to the body, and returns oxygen-poor blood back to the heart.
• Pulmonary circulation is the part of the cardiovascular system that carries oxygen-poor blood away from the
heart to the lungs, and returns oxygen-rich blood back to the heart.
• Organs of the lymphatic system include the tonsils, thymus, and spleen.
• The lymphatic system works with the cardiovascular system to return body fluids to the blood.
Review Questions
Recall
1. Identify the three main parts of the cardiovascular system.
2. Identify three types of blood vessels found in the body.
3. Which blood vessels move blood away from the heart?
4. What are the smallest blood vessels in the body called?
5. Which blood vessels bring blood back to the heart?
6. Identify three main organs of the lymphatic system.
7. Name one function of tonsils.
Apply Concepts
8. Where does blood in the pulmonary system go after it leaves the heart?
9. Where does blood in systemic circulation go after it leaves the heart?
10. What does blood that leaves the heart in systemic circulation have that body cells need?
11. How do the cardiovascular and lymphatic systems work together?
12. What is lymph, and where does it come from?
13. What might happen if a person did not have a spleen?
Critical Thinking
14. Explain how there are actually two circulatory systems in the body.
Further Reading / Supplemental Links
• http://en.wikipedia.org/wiki/Heart
Points to Consider
Next we look further at the heart and blood vessels.
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• How can the heart pump blood to the entire body?
• How do you think a hole in the heart muscle affect blood flow?
References
1. Mariana Ruiz Villarreal (User:LadyofHats/Wikimedia Commons). http://commons.wikimedia.org/wiki/Fi
le:Arterial_System_en.svg . Public Domain
2. Left: Patrick Lynch, C. Carl Jaffe, M.D.; Right: User:alexanderpiavas134/Wikipedia. Left: http://commons
.wikimedia.org/wiki/File:Heart_circulation_diagram.svg; Right: http://commons.wikimedia.org/wiki/File:Hu
mhrt2.jpg . Left: CC BY 2.5; Right: Public Domain
3. Laura Guerin. CK-12 Foundation . CC BY-NC 3.0
4. Laura Guerin. CK-12 Foundation . CC BY-NC 3.0
5. Courtesy of the National Cancer Institute. Capillaries connect arteries and veins . Public Domain
6. Sam McCabe. CK-12 Foundation . CC BY-NC 3.0
7. User:The Emirr/Wikimedia Commons. http://commons.wikimedia.org/wiki/File:TE-Lymphatic_system_diagr
am.svg . CC BY 3.0
8. Courtesy of the National Cancer Institute. http://commons.wikimedia.org/wiki/File:Illu_lymph_capillary.png
. Public Domain
9. Laura Guerin. CK-12 Foundation . CC BY-NC 3.0
10. Laura Guerin. CK-12 Foundation . CC BY-NC 3.0
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