Download The Heart A Muscle Activity

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ACTIVITY OVERVIEW
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1–2
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40
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The Heart—A Muscle
BO RA
T
SUMMARY
Students evaluate the strength of the heart muscle by attempting to pump water at
the same rate as their resting pulse (in beats per minute). They then compare the volume of water they pumped to the volume of blood the heart pumped in the same
amount of time.
KEY CONCEPTS AND PROCESS SKILLS
1.
Graphing data can reveal patterns that are not apparent from data tables.
2.
Creating models is one way to understand and communicate scientific
information.
3.
Systems in the human body help regulate the internal environment. For
example, the heart rate changes to keep blood oxygen levels in the range
required to survive.
4.
Human body systems are composed of organs. The structure of an organ is
adapted to perform specific functions within one or more systems.
5.
Blood is pumped around the human body by the heart. The heart acts as a
pump that works continuously without rest.
6.
Valves control the direction of flow and allow liquid to move under pressure
in both a pressure bulb and the human heart.
7.
The heart pumps a large volume of blood with each beat.
KEY VOCABULARY
function
range
model
structure
muscle
volume
Teacher’s Guide
B-135
Activity 22 • The Heart—A Muscle
MATERIALS AND ADVANCE PREPARATION
For the class
*
sponges
*
mops
For each group of four students
*
1
pressure bulb
2
45-cm (18-inch) lengths of clear plastic tubing
2
plastic bins (or buckets)
1
1-liter bottle or other measuring container, graduated into 100-mL
divisions
supply of water
1
meter stick (optional)
*
access to a wall clock or watch with a second hand
*
paper towels
*Not supplied in kit
If you do not have 1-liter flasks for measuring volume, ask students to bring
in clean, empty 1-liter soft drink bottles. Use a permanent pen and a graduated cylinder to calibrate the volume in 100-mL divisions.
If meter sticks are unavailable, use a measuring tape to mark heights in 1-inch
increments on a wall so students can easily measure their height in feet and
inches.
To prevent potential spills, fill one plastic bin 3⁄4 full of water for each group of
four students in advance. Also have sponges, mops, and paper towels available
to clean up any spills. Alternatively, you could conduct this activity outdoors.
TEACHING SUMMARY
Getting Started
1.
Discuss the heart as a muscle.
Doing the Activity
2.
Students record their resting pulse and then pump water.
Follow-Up
3.
B-136
Science and Life Issues
The class compares the heart with other muscles of the body.
The Heart—A Muscle • Activity 22
INTEGRATIONS
Mathematics
Reinforce graphing skills by having students create a bar graph of class data
(of resting pulse, volume of water pumped, or volume of blood pumped by
the heart). Discuss the range of student data.
BACKGROUND INFORMATION
Cardiac Output
While the size of a person’s body significantly affects pulse rate, people of the
same size can have a range of resting pulse values. People with a low pulse rate
for their size generally pump a larger volume of blood per pump (known as
stroke volume). Athletes tend to have low resting heart rates and high stroke
volumes. The efficiency of the heart (as exhibited by a lower resting heart
rate) is affected by a number of factors, such as overall physical condition,
stress, metabolism, and use of medications.
Cardiac output is the volume of blood the heart pumps out in a minute (stroke
volume x pulse rate). The heart of an average adult at rest pumps approximately the entire volume of blood around the body once a minute. When
exercising, an increase in the stroke volume and an increase in pulse rate work
together to increase the cardiac output, up to five times the output at rest.
Students can estimate their own cardiac outputs based on their heights (as
presented in Figure 1 on page B-62 in the Student Book). (In fact, cardiac output is more closely related to body mass. However, height is easier to measure
in the classroom and is not as sensitive a subject as body mass.)
Cardiac output is an important indicator of heart health. It can be reduced if
the heart valves are damaged and/or the arteries are narrowed because of
heart disease. Reduced cardiac output will tend to increase the heart rate, and
a faster pulse increases the workload on the heart. Reduced cardiac output
will also reduce the amount of blood getting to the tissues, which causes
fatigue, especially during exertion.
The heart starts beating about 7 months before birth and keeps beating until
death. This works out to be around 3 billion beats in an average life span. A
baby has a pulse of about 130 beats per minute. By adulthood, most people
have a resting pulse of about 70. The heart’s failure to keep beating is the leading cause of death in most developed countries.
Teacher’s Guide
B-137
The Heart—A Muscle • Activity 22
TEACHING SUGGESTIONS
n
GETTING STARTED
1.
Discuss the heart as a muscle.
Have students feel the muscles in their upper arms.
n
2.
DOING THE ACTIVIT Y
Students record their resting pulse and then
pump water.
Ask, How is your heart muscle similar to and differ-
In the first part of the activity, students measure
ent from muscles in your arms? Responses may
their resting pulse in beats per minute, as was done
include that the heart muscle is not attached to
in Activity 19, “Heart-ily Fit.” If necessary, review
bones and that it works all the time. Students may
how to measure resting pulse.
wonder how the heart expands again after the muscle has contracted. It is partly due to the elastic
recoil of the heart muscle; like the pressure bulb,
the heart returns to its resting shape. Very fit people and young people tend to have more elastic
hearts than others.
Inform students that, when completing Step 4 of the
Procedure, they should use one hand only and pump
the bulb the same number of times as their resting
heart rate in one minute. Many students will be able
to pump at about the same rate as their heart (as measured by their resting pulse). If they are not able to
Tell students that in this activity they will evaluate
pump the bulb that number of times in a minute,
how hard the heart muscle works, as well as the
they should stop at the end of one minute and record
amount of blood it is able to pump each minute.
the number of times they were able to pump the bulb.
Review the Challenge (“How can you measure how
hard your heart muscle works?”) with the class.
Point out that they will measure volume, which
can be defined as the amount of space something
occupies.
This activity provides an excellent opportunity to
assess students on either element (“Task Management” or “Group Participation”) of the GROUP
GI
INTERACTION (GI) variable. If you plan to use
Remind students that as soon as they finish pumping the water each person should measure the volume of water pumped as well as record how his or
her hand feels. This is especially important because
all the water should be returned to the original container before the next student begins pumping.
Have students work in groups of four to complete
the Procedure.
this assessment with your students, inform
After they have completed the Procedure, make sure
them in advance and be sure you have enough time
they know, or can measure, their height. Students
to evaluate every group.
need this information to answer Analysis Question 2.
(They may be surprised to find they are an inch taller
than the last time they measured!) A few students
may need help comparing their data to the chart.
Teacher’s Guide
B-139
Activity 22 • The Heart—A Muscle
n
3.
FOLLOW–UP
SUGGESTED ANSWERS
TO ANALYSIS QUESTIONS
The class compares the heart with other
muscles of the body.
1.
Compare the pressure pump model to what
Ask, Your heart is a muscle. Do you think it is stronger
you know about your heart. In what ways
or weaker than the muscles in your hand? The heart
do you think the pressure bulb is a good model for
is a very strong muscle that must work continuous-
your heart? What were the weaknesses of the pres-
ly. You may wish to point out that the heart is an
sure bulb as a model for the heart?
involuntary muscle and is controlled by the nervous system. Its ability to work continuously
The pressure bulb modeled the pumping func-
requires an uninterrupted blood supply, which is
tion of the heart. It also has valves that force
provided by the coronary arteries that are visible on
water to go in one direction, just like in the
the outside of the heart.
heart. The pressure bulb is slightly smaller than
a real heart and may not accurately approxi-
After students have completed Analysis Question 1,
mate the pressure that the heart exerts.
you may want them to compare the range of resting
pulses. Ask, How many of you were able to pump the
2.
Use Figure 1, on the following page, to find
same volume of blood as your heart does? Emphasize
out how much blood your heart pumps per minute
the idea that the heart pumps the same blood
based on your height.
through the body again and again. In an adult, the
total volume of blood in the body is 5–6 L. If appro-
a.
Record the volume of blood (in liters) pumped
by your heart each minute.
priate, have students create a bar graph of class data
(as described in the Integrations section).
Responses are likely to range from 3–5 liters.
Ask, You were able to rest the muscles of your hand at
b.
Compare the amount of blood your heart pumps
the end of one minute. When do you think your heart
each minute to the amount of water you were
muscle rests? Although many students may answer
able to pump: Was it more? Was it less? By how
“never,” the heart does rest between beats. This is
much?
one reason why stimulating one’s heart through
Students are likely to have pumped 1.5–3 liters.
smoking, drugs, or high stress levels can be detri-
If students report pumping more than 3 liters,
mental. An extremely well-conditioned athlete,
ask if they pumped with only one hand and
such as a marathon runner who has a resting pulse
whether they made a real effort to pump ap-
of 30–40 beats per minute, has a heart that is not
proximately the same number of times as their
only pumping with great efficiency but one that is
heart beats in a minute. Generally, students
also getting more resting time.
report that their heart pumps a greater volume
of blood per minute than the volume of water
they pumped with their hand. Some will find
that their heart pumps two or more times as
much volume as they pumped per minute.
B-140
Science and Life Issues
The Heart—A Muscle • Activity 22
4.
Figure 1: Heart Output
Why do you think that exercising regularly decreases
your heart rate?
Height
(feet and
inches)
Volume
of Blood
(liters per
minutes)
Height
(feet and
inches)
Volume
of Blood
(liters per
minutes)
4'0''
3.00
5'1''
4.38
ing exercise. Ask them to consider how a faster
4'1''
3.13
5'2''
4.50
heart rate will affect the volume of blood being
4'2''
3.25
5'3''
4.63
4'3''
3.38
5'4''
4.75
pulses than the general public. However, their
4'4''
3.50
5'5''
4.88
hearts pump the same volume of blood as the
4'5''
3.63
5'6''
4.95
4'6''
3.70
5'7''
5.00
heart have more tensile strength, are more elas-
4'7''
3.75
5'8''
5.13
tic, can expand more, and can pump more
4'8''
3.88
5'9''
5.25
4'9''
4.00
5'10''
5.38
4'10''
4.13
5'11”
5.45
4'11''
4.20
6'0”
5.50
5'0''
4.25
Just like other muscles, the heart muscle is
strengthened by regular exercise. Have students
think about what happens to the heart rate dur-
pumped and how hard the heart is working.
Well-conditioned athletes have lower resting
average person. Each stroke of an athlete’s heart
pumps more blood because the walls of the
forcefully. This ability is lost very quickly, however, when training ceases.
3.
Describe how hard your heart works by using quantitative and qualitative data from the activity. Hint: Be
sure to look at your notes from this activity.
The heart is a muscle that works hard. It beats
about 60–80 times a minute and pumps between 3–6 liters of blood a minute. Using their
hands to pump, most students will be able to
approximate their resting pulse, but are likely
to have pumped about half of the amount of
fluid their heart pumps. Most students are also
likely to report that their hand was very tired.
This comparison can give them a feeling for
how hard their heart muscle works.
Teacher’s Guide
B-141