Download Unit A - apel slice

Lesson 3
How Do Body Systems Work Together?
Fast Fact
---see picture
Miles and Miles The average adult's brain has about 100 billion nerve cells like those
shown here. If laid end to end, these cells would extend about 3.2 million km (2
million mi)! Nerve cells help your brain react to your environment. In the
Investigate, you'll test your own reaction time.
46
Testing Reaction Time
Materials
 metric ruler
 reaction time chart
Procedure
1. Sit with your arm resting on a table and your wrist hanging over the edge. Hold your
hand sideways, ready to catch the ruler with your fingers.
2. Have your partner hold the ruler above and perpendicular to your hand, so you'll be
able to catch it.
3. Have your partner let go of the ruler. Try to catch it as quickly as possible.
4. Note the measurement on the ruler, at the place where you caught it. Compare this
number to the reaction time chart to find out how long it took you to catch the ruler.
Record your results.
---see chart
5. Repeat Step 4 three times, and then trade places with your partner. Make graphs to
compare your results.
Draw Conclusions
1. How did your reaction time change with each trial? Why?
2. Inquiry Skill What can you infer about the messages your brain receives and sends
to enable you to catch the ruler?
Investigate Further
Now you know how to measure reaction time. Hypothesize how you might improve
yours. Plan and conduct an experiment that would test your hypothesis.
47
Reading in Science
VOCABULARY
circulatory system p.48
respiratory system p. 51
skeletal system p. 52
muscular system p. 52
nervous system p. 54
excretory system p. 56
SCIENCE CONCEPTS
 that the body has different systems with different roles
 how body systems interact
READING FOCUS SKILL
SEQUENCE Look for ways to organize in steps the processes described in this lesson.
Circulatory System
If you were asked to identify the most important system in the body, which would you
choose? Though all of the body's systems perform important functions, the
circulatory system is one of the most vital. It pumps blood to all parts of the body.
The circulatory system is made up of the heart, the blood vessels, and the blood.
Together, these parts of the circulatory system transport oxygen, nutrients, and
wastes through the body.
Blood is a connective tissue made up of several parts. The liquid part, called plasma, is
mostly water. Nutrients from food and waste products from cells dissolve in
plasma. Nutrients are carried to the body's cells. Waste products, which result from
cell functions, are carried away from the cells so that they can be removed from the
body.
The solid part of blood includes red blood cells, white blood cells, and platelets. Red
blood cells carry oxygen to all body cells. White blood cells help fight infection.
Platelets help the blood clot and stop bleeding from wounds.
Blood leaves the heart through blood vessels called arteries. Arteries lead to small blood
vessels called capillaries (kAp•uh•lair•eez). Capillaries are so tiny that blood cells
move through them in single file. Capillaries lead to larger blood vessels called
veins. Veins return blood to the heart.
Blood is a kind of connective tissue that is part of the circulatory system. It travels
through blood vessels, carrying oxygen and nutrients to body cells and
carrying wastes away from body cells. Blood vessels are one kind of organ of
the circulatory system.
48
Oxygen and nutrients move from the blood into cells through capillary walls.
Your heart beats at a steady rate, pushing blood into your arteries. The heart is
made of cardiac muscle.
For a more detailed look at the circulatory system, see the Health Handbook.
The circulatory system is made up of the heart, blood, capillaries, veins, and
arteries. Together, these organs and tissues provide your body's cells with the
oxygen and nutrients they need. They also help body cells get rid of wastes.
The pump in the circulatory system is the heart. Made mostly of muscle tissue, the heart
is really a double pump. It receives blood from the lungs and pumps it to the body.
At the same time, it receives blood from the body and sends it to the lungs.
SEQUENCE How does blood flow from the lungs through the body?
49
The lungs are the major organs of the respiratory system.
The exchange of carbon dioxide for oxygen takes place in the alveoli—tiny air sacs
in the lungs.
Math in Science
Interpret Data
The bar graph shows the amount of oxygen your body needs for various activities.
How does physical activity affect the amount of oxygen the body needs?
---see chart
50
Respiratory System
Think of all the things you do each day. You go to school, you might play on a sports
team, you participate in clubs, you play outdoors, and you do homework. You need
a lot of energy! So your cells need a lot of oxygen. The respiratory system is a
group of organs and tissues that exchange oxygen and carbon dioxide between your
body and the environment.
When you breathe, your body gets the oxygen it needs. Tiny hairs in your nose filter the
air you inhale. Next, capillaries in your nasal passages warm the air. Warm, clean
air then travels down your trachea, or windpipe. In your chest, the trachea branches
into two large tubes called bronchi (BRAHNG•ky). Each bronchus leads to a lung.
The lungs are the main organs of your respiratory system. In the lungs, the bronchi
branch into smaller and smaller tubes. At the end of the smallest tubes are tiny air
sacs called alveoli (al•vEE•uh•ly). The walls of the alveoli are only one cell thick
and are surrounded by capillaries. Gases are exchanged between the air in the
alveoli and blood in the capillaries.
The capillaries of the alveoli receive oxygen-poor blood from the heart. This blood
contains a lot of carbon dioxide (CO2). Your body produces CO2 as a waste product
of cell functions. CO2 passes from the blood plasma into the alveoli. Your body
gets rid of the CO2 when you exhale. Oxygen from the air you inhale passes into
the blood, and red blood cells pick up the oxygen. Oxygen-rich blood travels back
to the heart. From the heart, it is pumped throughout the body, to every body cell.
SEQUENCE How does oxygen get from the air into your blood?
Pulmonary Circulation
The heart pumps oxygen-poor blood through the pulmonary arteries to the lungs.
There, the blood picks up oxygen. The oxygen-rich blood travels back to the
heart through the pulmonary veins. The circulatory system has blood vessels
that provide blood for the heart muscle itself.
51
Skeletal and Muscular Systems
Imagine a mammal with no skeleton. Do you picture a shapeless blob on the ground?
That's probably what the mammal would look like!
Your skeletal system, which includes mainly bones, gives your body its form and
protects many of your organs. The skeletal system works with your muscular
system. The muscular system includes muscles and tendons that move bones.
The skeletal system includes bones, cartilage, and ligaments. An adult's skeleton is
made up of 206 bones. Cartilage is spongy connective tissue that cushions the ends
of many bones. Bands of connective tissue called ligaments hold bones together.
Without your skeleton's well-organized bony structure, you would not be able to sit,
stand, or move. Your brain, heart, and lungs would be at risk of injury, and your
circulatory system would lack blood cells. That's because blood cells are produced
inside your largest bones.
---see pictures
The bones at this joint are held together by ligaments. Muscles are attached to
bones by tendons.
The skeletal system supports your body. It also protects many of your internal
organs.
For a more detailed look at the skeletal and muscular systems, see the Health
Handbook.
52
Skeletal muscles work with the skeletal system to help you move your body.
You're probably aware of the muscles that support and move your body. These muscles
are skeletal muscles. They are made of groups of muscle tissue held together by
connective tissue. Skeletal muscles usually are attached to bones, either directly or
by bands of connective tissue called tendons.
Skeletal muscles often work in pairs. This means that one muscle contracts to bend a
joint and another muscle contracts to straighten it. Skeletal muscles are voluntary
muscles, because you can control them.
There are two other kinds of muscle. Smooth muscle makes up most of the walls of the
body's organs, including blood vessels and digestive organs. There, contractions
help move blood or food through tubes. Cardiac muscle makes up the walls of the
heart. It contracts strongly to pump blood to all parts of the body. These two types
of muscles are sometimes called involuntary muscles—you can't control their
movements.
SEQUENCE How do opposing muscles cause movement at a joint?
Insta-Lab
Muscle Contraction
Measure around your upper arm when your elbow is straight and when it's bent. Record
and compare the measurements. Describe the muscle that you infer controls the
bending of your arm. Explain your reasoning.
53
Nervous System
Your nervous system enables you to sense your environment and to react to it. The
nervous system directs other systems' activities, and it connects all the tissues and
organs in your body to your brain. It is amazing, but it is the least-understood part
of your body.
The nervous system has two parts. The central nervous system is made up of the brain
and spinal cord. The spinal cord is a bundle of nerves, about as thick as a pencil,
that extends from the brain all the way to the hips. The central nervous system
receives and interprets signals from the nerves throughout the body. The central
nervous system sends signals up and down the spinal cord and determines
responses that are needed. The brain sends signals through nerves that direct all of
the body's voluntary muscles. It also controls the body's automatic functions, like
contraction of cardiac muscle, respiration, digestion, and circulation.
The peripheral (puh•RIF•uh•ruhl) nervous system is made up of sensory organs, such as
your eyes and ears, and touch sensors in your skin.
Nerves connect the central nervous system—the brain and spinal cord—and all
other parts of the body.
For a more detailed look at the nervous system, see the Health Handbook.
A synapse (siN•aps) is a connection between nerve cells. Chemical signals travel
across synapses, helping to send messages to and from the brain.
54
If you accidentally prick your finger on a thorn, your hand pulls back in a reflex
action. This happens even before the information travels to your brain. The
nerve signal triggered by the thorn takes a "shortcut," signaling the spinal
cord to "tell" the muscles in your arm to pull your hand out of danger.
Sensory organs have special nerves called sensory receptors. The receptors detect
changes in your surroundings and send signals along nerves to the central nervous
system. Sensory receptors in your ears, for example, detect vibrations. They "tell"
your brain about the vibrations, and the brain interprets them as sounds.
Has your doctor ever struck your knee with a small rubber mallet? If so, you likely
experienced a reflex response. Reflexes are automatic responses to certain stimuli.
When the doctor struck your knee, a nerve signal traveled to your spinal cord,
whereit took a "shortcut." Before traveling on to your brain, the signal in your
spinal cord triggered a nerve in your muscles to jerk your leg. You kicked before
your brain was even aware there was a tap!
Reflexes often occur in response to stimuli that cause pain. The brain is bypassed at
first. Your vulnerable body part is quickly pulled from the source of the pain.
Eventually, your brain senses the pain—but not until after your body has responded
to it.
SEQUENCE What is the sequence of events in a reflex?
55
Excretory System
You know that body systems work together to carry out life functions. They digest food
and release nutrients. They carry oxygen and nutrients to body cells, and they
remove wastes from body cells. Carbon dioxide is eliminated when you exhale. But
other wastes, such as ammonia, are removed from the body by the excretory
system.
Ammonia, a waste product of certain cell functions, enters the blood. It is carried by
blood plasma to the liver. The liver converts ammonia into urea, which travels
through the blood to the kidneys. As blood flows through the kidneys, the main
organs of the excretory system, urea and other wastes are filtered from the blood.
The result is urine. Urine flows through tubes called ureters to a muscular organ
called the bladder. When the bladder is full, urine is then eliminated from the body.
SEQUENCE How is ammonia removed from the body?
Liquid wastes are removed from the blood through capillaries in the kidneys.
Materials the body needs, mostly water and salts, are returned to the blood.
For a more detailed look at the excretory system, see the Health Handbook.
The kidneys filter liquid wastes from the blood and help remove them from the
body as urine.
56
1. SEQUENCE Draw and complete the graphic organizer.
---see chart
2. SUMMARIZE Use the graphic organizer to write two or three sentences about the
movement of oxygen in the respiratory system.
3. DRAW CONCLUSIONS Between the trachea and the esophagus is a flap of tissue
that closes when you swallow. What is its function?
4. VOCABULARY Use the information in the lesson to write a clue for each
vocabulary term. Then hide each term in a grid of letters to make a word-search
puzzle.
Reading Review
Test Prep
5. Critical Thinking In what ways do the digestive and circulatory systems work
together?
6. Tendons are connective tissues that
A. make blood cells.
B. carry signals from nerves.
C. connect bones to bones.
D. connect muscles to bones.
Writing
Expository Writing
Write a biography about Percy Lavon Julian. Explain how his research helped doctors
better understand how the body is affected by disease.
Art
Pointillism
In the nineteenth-century style of painting called pointillism, pictures were painted with
small dots of color. The brain interprets the many dots as smooth forms. Make a
picture of your classroom, using the pointillism style.
Physical Education
Circulatory System
You can improve the health of your circulatory system by lowering your resting
heartbeat rate. Measure your heartbeat rate at rest. Then exercise for 30 minutes a
day for a month. How much does your resting heartbeat rate drop?
For more links and activities, go to www.hspscience.com
57