The Circulatory System
The circulatory system
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Is the organ system made up of the heart, blood vessels, and blood
The role of the circulatory system is transportation
The heart is a pump that pushes blood through blood vessels
Blood vessels are a network of tubes throughout the entire body, which allows the blood to
reach all parts
Blood
 Blood is a type of connective tissue made up of four parts: red blood cells, white blood cells,
platelets, and plasma
 Blood transports oxygen and nutrients to cells
 Blood moves hormones, disease-fighting materials, and even thermal energy around the body
 Blood removes waste from the body tissues for disposal: carbon dioxide to the lungs, where it is
released into the air, and other wastes to the kidneys.
 Stem cells in your bone marrow are constantly producing new blood cells to replace lost,
damaged, or aging blood cells
 Each type of blood cell performs a specific task
Blood
Component
What it looks like
Description
Function
Red blood cell
Red blood cells make
up half the blood by
volume. They are
bright red and lack
nuclei
Red blood cells contain
hemoglobin, a protein
that picks up oxygen
and carbon dioxide
White blood cell
White blood cells make
up only 1% of blood by
volume.
White blood cells fight
and destroy diseasecausing bacteria and
viruses.
Platelet
Platelets are small cells
that make up less than
1 % of blood by
volume.
Platelets are small cells
that help the blood
clot, seal wounds, and
stop bleeding.
Plasma
Plasma is the proteinrich liquid in which
blood cells float. It
makes up half the
blood by volume
Plasma carries blood
cells, dissolved wastes,
nutrients, and
hormones.
The Heart
 Heart is organized into four chambers – two upper and two lower
 A special group of heart cells called pacemaker cells send an electrical signal. This signal tells the
muscles in the walls of the upper chambers to contract. This pushes blood into the larger, lower
chambers. One-tenth of a second later, the pacemaker cells’ signal reaches the lower chambers,
causing them to contract.
 Valves in the heart keep the blood flowing smoothly in the right direction.
 Cardiac muscles do not tire as other muscles do. They continue to regularly contract for our
entire lives.
 Your heart beats according to your body’s need for oxygen.
Blood Vessels
 A network of tubes that carry blood throughout the body.
 Three types of blood vessels: arteries, veins, and capillaries.
 They are lined with a smooth layer of epithelial tissue which allows the blood to move through
the vessels easily.
Arteries
 A blood vessel that carries blood away from the heart.
 Because blood is squeezed into the arteries, blood is under more pressure than in any of the
other blood vessels. Therefore, arteries have thick, muscular walls to withstand this pressure,
and to help move the blood along
Veins
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A blood vessel that carries blood back toward the heart.
Valves in the veins make sure the blood continues to flow in the correct direction
Capillaries
 Blood vessels are largest near the heart
 Farther from the heart, they branch into smaller and smaller vessels called capillaries
 A tiny blood vessel with very thin walls that are only one cell thick
 Are so narrow that red blood cells can only travel in single file.
 Link arteries and veins together
 Thin walls allow oxygen and nutrients to easily diffuse from the blood into the cells
 The opposite occurs with carbon dioxide and other wastes
 Carbon dioxide goes to the lungs and other wastes go to the kidneys
Arteries
Veins
Capillaries
Circulation of blood
The right side of the heart pumps blood to the lungs. Gas exchange takes place in the lungs: blood
absorbs oxygen and gives off carbon dioxide.
The oxygen-rich blood then travels back from the lungs to the left side of the heart. From here, the
heart pumps the blood to the rest of the body through the arteries. The arteries divide into smaller and
smaller vessels, until they are capillaries. From the capillaries, oxygen and other substances diffuse out
of the blood into the surrounding tissues. Wastes can also diffuse from these tissues into the blood to be
carried away.
Some of the blood goes to the kidneys. The kidneys remove most of the waste substances from the
blood. The blood then flows from capillaries into veins. It completes the circuit as it returns to the right
side of the heart.
Questions
1. Explain the function of the circulatory system and each of its parts
2. Describe how the circulatory system is related to the respiratory system
3. An athlete measures how fast his heart is beating before and immediately after a race. What is he
likely to observe? Why?
4. Describe the path of a red blood cell as it travels through the entire circulatory system, beginning and
ending at the heart. Include information about its route and activities.
5. Make a chart listing the major differences between the three types of blood vessels.
6. Using the diagram of the heart see if you can follow the path of blood through the heart. List each
part of the heart in the order that the blood travels through.
7. The heart consists of how many chambers?
8. Explain the role of the pacemaker cells.
9. What four parts make up blood?
10. What is the role of white blood cells?
11. Where do most wastes from cells end up?
12. What is the main role of the circulatory system?