Human Anatomy, Physiology, and Health Sciences

Our Body Works Together

Your body is amazing. It is made of many parts, and each part has a job to do.

But the body does not work as separate pieces. The parts of your body work together as one team. When one part helps another part, your whole body can move, grow, think, and stay healthy.

This is called an integrated system. That means many body parts and body systems work together.

What is a body system?

A body system is a group of body parts that do a big job together. Your body has many systems, and each one helps keep you alive and well.

Let’s learn about some important body systems.

1. The skeletal system

Your skeletal system is made of your bones. Bones give your body shape. Bones also help hold you up and protect parts inside your body.

• Your skull protects your brain.
• Your ribs help protect your heart and lungs.
• Your leg bones help you stand and walk.

2. The muscular system

Your muscles help you move. You use muscles when you run, jump, smile, and blink.

Muscles and bones work together. Bones give support, and muscles pull on bones to make movement happen.

3. The respiratory system

Your respiratory system helps you breathe. The lungs take in air.

Your body needs oxygen from the air. Oxygen helps your body have energy for all its jobs.

4. The circulatory system

Your circulatory system includes your heart and blood. Your heart pumps blood through your body.

Blood carries oxygen and food to body parts. Blood also helps carry waste away.

5. The digestive system

Your digestive system helps break down food. Food gives your body energy and helps you grow.

When you eat, your body changes food into tiny parts your body can use.

6. The nervous system

Your nervous system includes your brain, spinal cord, and nerves. This system helps you think, feel, learn, and remember.

It also sends messages through your body. For example, your brain tells your legs to walk and your hands to clap.

How body systems work together

No body system works all alone. Systems help one another every day.

• You eat food with help from your digestive system.
• Your digestive system gets nutrients from food.
• Your circulatory system carries those nutrients through your blood.
• Your respiratory system brings in oxygen.
• Your circulatory system carries oxygen to body parts.
• Your muscles use oxygen and nutrients to move.
• Your nervous system tells your muscles when and how to move.
• Your bones support your body while you move.

That means eating, breathing, moving, and thinking are all connected.

An easy way to think about it

Think of your body like a team. On a team, each player has a job. But the team does best when everyone works together.

Your heart, lungs, brain, muscles, bones, and stomach all have jobs. Together they help you live.

Example: running on the playground

When you run, many systems work together at the same time.

1. Your brain tells your body to start running.
2. Your muscles move your legs and arms.
3. Your bones support your body.
4. Your lungs bring in more oxygen.
5. Your heart pumps blood faster to carry oxygen.
6. Your body uses energy from food.

You may feel your heart beat faster and your breathing get quicker. That is your body systems helping each other.

Example: eating lunch

When you eat lunch, body systems work together too.

1. You see your food with your eyes and decide to eat.
2. Your brain helps you chew and swallow.
3. Your digestive system breaks down the food.
4. Your blood carries nutrients from the food.
5. Your body uses the nutrients for energy and growth.

So even a simple lunch uses many parts of the body.

Example: touching something cold

Let’s look at another example.

1. Your hand touches something cold.
2. Nerves send a message to your brain.
3. Your brain understands, “That is cold!”
4. Your brain sends a message back.
5. Your muscles move your hand away.
6. Your bones help your arm move.

This shows that the nervous system, muscular system, and skeletal system work together.

Worked Example 1: What helps you kick a ball?

Question: If you kick a ball, which body parts are working together?

Think: You need to know to kick, move your leg, and stay standing.

Answer:

• Your brain and nerves tell your body what to do.
• Your muscles move your leg.
• Your bones support your body.

So: Kicking a ball takes teamwork inside your body.

Worked Example 2: Why do you breathe faster when you run?

Question: Why does breathing get faster when you run?

Think: Running makes muscles work hard.

Answer: Your muscles need more oxygen when you run. Your lungs bring in more air, and your heart pumps blood faster to carry oxygen.

So: The respiratory system and circulatory system help your muscles do their job.

Worked Example 3: How does food help you play?

Question: You eat breakfast and then play outside. How does your body use the food?

Think: Food must be changed and carried.

Answer:

• Your digestive system breaks down the food.
• Your blood carries nutrients from the food.
• Your muscles use that energy to play.

So: Eating helps your whole body because systems work together.

How to keep body systems healthy

Because body systems work together, taking care of your body helps all of it.

• Eat healthy foods to help your body grow.
• Drink water to help your body work well.
• Exercise and play to make muscles, heart, and lungs strong.
• Sleep to help your brain and body rest.
• Wash your hands to help keep germs away.
• Wear safety gear like a helmet to protect your body.

Important idea to remember

Your body is not just one part. It is many parts working together at the same time.

Your brain, heart, lungs, stomach, muscles, bones, and blood all help one another. That is why the human body is an integrated system.

Brief Summary

The human body is made of many systems, such as the skeletal, muscular, respiratory, circulatory, digestive, and nervous systems. Each system has its own job, but no system works alone. They depend on one another so you can eat, move, breathe, think, grow, and stay healthy.

The Muscular System and Movement

Your body can move in many ways. You can walk, jump, smile, blink, and wave. You can even breathe while you sleep. Your muscular system helps you do all of these things.

Muscles are body parts that can squeeze and let go. When a muscle squeezes, it gets shorter and tighter. When it lets go, it gets longer and softer. This helps body parts move.

Kinematics is a big word. It means how things move. In 1st grade, we can think about kinematics as noticing if something moves fast or slow, up or down, and back and forth.

What are muscles?

Muscles are found all over your body. They work with your bones to help you move. Bones are hard. Muscles are softer. Muscles pull on bones so your body can bend and straighten.

For example, when you bend your arm, muscles in your arm pull to move your lower arm. When you straighten your arm, another muscle helps pull the other way. Muscles work as a team.

What do muscles do?

• Help you move by pulling on bones
• Help you stand and sit up
• Help you make faces like smiling and frowning
• Help you breathe
• Help your heart beat

Some movements are ones you choose, like hopping or clapping. These are called voluntary movements. Some movements happen without you thinking about them, like your heart beating and your chest moving as you breathe. These are called involuntary movements.

Muscles and bones work together

Your muscles do not push your bones. They pull on them. Joints are places where bones meet, like your elbow, knee, and shoulder. When muscles pull near a joint, the body part moves.

Think about your elbow. One muscle helps bend your arm. Another muscle helps straighten it. One pulls, then the other pulls. This teamwork helps your body move smoothly.

How things move

We can describe movement in simple ways:

• Fast or slow
• Up or down
• Forward or backward
• Still or moving

When you run, your leg muscles help your legs move fast. When you tiptoe, your leg and foot muscles help you move slowly and carefully. When you nod your head, neck muscles help it move up and down.

Muscles can get tired

If you jump many times, your legs may feel tired. That is because your muscles have been working hard. Muscles need rest, healthy food, and water to help them do their jobs.

Exercise helps muscles grow stronger. Running, climbing, dancing, stretching, and playing outside are good ways to help muscles stay healthy.

Worked Example 1: Bending an arm

Question: What helps your lower arm move when you bend your elbow?

Step 1: Look at the body part that moves. The lower arm moves.

Step 2: Think about what pulls on bones. Muscles pull on bones.

Answer: The muscles help your lower arm move by pulling near the elbow joint.

Worked Example 2: Choosing the movement word

Question: Mia is walking to class. Is her body still or moving?

Step 1: Walking means going from one place to another.

Step 2: If someone goes from one place to another, that person is moving.

Answer: Mia is moving.

Worked Example 3: Fast or slow

Question: Ben is racing on the playground. Are his leg muscles helping him move fast or slow?

Step 1: A race usually means going quickly.

Step 2: His muscles are helping his legs move quickly.

Answer: His leg muscles are helping him move fast.

Worked Example 4: Voluntary or not

Question: You smile for a picture. Is that something you choose to do, or does it happen without thinking?

Step 1: Smiling for a picture is something you decide to do.

Step 2: Movements you choose are voluntary movements.

Answer: Smiling for a picture is a voluntary movement.

Let’s remember

• Muscles help your body move.
• Muscles squeeze and let go.
• Muscles pull on bones near joints.
• Muscles help with movements you choose and movements your body does on its own.
• We can describe movement as fast, slow, up, down, still, or moving.
• Rest, water, healthy food, and exercise help muscles stay healthy.

Brief Summary

Your muscular system is the group of muscles in your body. These muscles work with your bones and joints to help you move. They help you do big movements, like running, and small movements, like blinking and smiling. Learning how body parts move helps us understand kinematics, or how things move.

The Respiratory System

Your body needs air to live. The respiratory system is the body system that helps you breathe in and breathe out.

When you breathe in, your body takes in air. That air has oxygen in it. Oxygen is something your body needs to help you move, play, grow, and stay alive.

When you breathe out, your body gets rid of a waste gas called carbon dioxide. Your body does not need this gas, so breathing out helps remove it.

Let’s learn about the main parts that help you breathe.

Main Parts of the Respiratory System

• Nose and mouth: Air can enter your body through your nose or your mouth.
• Trachea: This is the air tube in your neck. It carries air down toward your lungs.
• Lungs: These are two soft organs in your chest. They fill with air when you breathe in and let air out when you breathe out.

How Breathing Works

1. You breathe in air through your nose or mouth.
2. The air travels down the trachea.
3. The air goes into your lungs.
4. Your body takes the oxygen from the air.
5. You breathe out and send out carbon dioxide.

You can feel breathing happening all day. Put your hand on your chest. When you breathe in, your chest rises. When you breathe out, your chest falls.

Why Oxygen Is Important

Every part of your body needs oxygen. Your muscles need oxygen to run and jump. Your brain needs oxygen to think and learn. Your whole body works better when it gets the oxygen it needs.

Why We Breathe Out Carbon Dioxide

As your body works, it makes carbon dioxide. This is a waste gas. Your respiratory system helps send it out when you breathe out.

The Lungs Work All the Time

Your lungs work when you are awake. They also work when you are asleep. You do not have to remind your lungs to breathe. Your body keeps breathing for you.

Breathing Faster and Slower

Sometimes you breathe slowly, like when you are resting. Sometimes you breathe faster, like after running or playing. That is because your body needs more oxygen when you move a lot.

Keeping the Respiratory System Healthy

• Breathe clean air when you can.
• Stay away from smoke.
• Cover your mouth and nose when you cough or sneeze.
• Wash your hands to help stop germs.
• Exercise and play to help keep your body strong.

Worked Examples

Example 1: What happens when you breathe in?

Question: Mia takes a big breath in. Where does the air go?

Answer: The air goes in through her nose or mouth, down the trachea, and into her lungs.

Example 2: What do lungs take from the air?

Question: Jay asks, “What does my body need from air?”

Answer: Your body needs oxygen from the air.

Example 3: What happens when you breathe out?

Question: Ana breathes out after running. What gas is her body sending out?

Answer: Her body is sending out carbon dioxide.

Example 4: Why are you breathing fast?

Question: Leo runs across the playground. Now he is breathing fast. Why?

Answer: His body needs more oxygen after running, so he breathes faster.

Let’s Remember

• The respiratory system helps you breathe.
• Air goes in through the nose or mouth.
• Air travels down the trachea.
• The lungs take in oxygen.
• Your body breathes out carbon dioxide.

Brief Summary

The respiratory system is the part of your body that helps you breathe. Air goes in through your nose or mouth, down the trachea, and into the lungs. Your body takes in oxygen and breathes out carbon dioxide. This system helps your body stay alive and healthy every day.

The Nervous System

Your body is always busy. It breathes, moves, feels, learns, and remembers. The nervous system is the body system that helps control all of these jobs.

The nervous system is like a fast message system. It sends and receives messages all around your body. These messages help you know what is happening and help your body decide what to do next.

The three main parts of the nervous system are the brain, the spinal cord, and the nerves.

• Brain: the control center of the body
• Spinal cord: the long bundle that carries messages between the brain and body
• Nerves: tiny pathways that carry messages to and from all body parts

What does the brain do?

The brain is inside your skull. It helps you think, learn, remember, and feel emotions. It also helps control breathing, heartbeat, balance, and movement.

When you read a book, tie your shoes, smell cookies, or laugh at a joke, your brain is working. Even when you are asleep, your brain is still busy helping your body.

What does the spinal cord do?

The spinal cord is a thick bundle of nerves that runs down your back. It connects the brain to the rest of the body.

Messages travel from the brain down the spinal cord and out to the body. Messages also travel from the body up the spinal cord to the brain.

What do nerves do?

Nerves are found all over your body. They are like little roads for messages. Some nerves carry messages from your senses to your brain. Other nerves carry messages from your brain to your muscles.

Because of nerves, you can feel a soft blanket, hear music, see colors, and pull your hand away from something hot.

How does the nervous system work?

Your nervous system works by sending messages very quickly. These messages help your body react.

Here is a simple way it happens:

1. Your senses notice something.
2. Nerves send a message to the brain.
3. The brain understands the message.
4. The brain sends a message back through nerves.
5. Your body responds.

For example, if you touch ice, nerves in your skin send a message to your brain: “This feels very cold!” Then your brain may tell your hand to let go.

The five senses and the nervous system

Your nervous system works closely with your five senses:

• Sight: your eyes send messages about light and color
• Hearing: your ears send messages about sounds
• Smell: your nose sends messages about odors
• Taste: your tongue sends messages about flavors
• Touch: your skin sends messages about pressure, temperature, and pain

Your brain puts all of this information together so you can understand the world around you.

The nervous system helps with movement

When you want to move, your brain sends messages through the spinal cord and nerves to your muscles. Then your muscles move.

If you decide to wave, kick a ball, or jump, your nervous system helps make that happen. Your brain plans the movement, and the nerves help carry the message.

The nervous system also protects you

The nervous system helps keep you safe. If something is too hot, too sharp, or too loud, your body can react quickly.

Sometimes your body reacts before you even think about it. For example, if you step on something sharp, you may lift your foot right away. This quick action helps protect your body.

Worked Example 1: Feeling something hot

Question: Mia touches a hot pan by accident. What happens in her nervous system?

Step 1: The skin on Mia’s hand feels the heat.

Step 2: Nerves send a message to the brain through the spinal cord.

Step 3: The brain understands: “That is hot!”

Step 4: The brain sends a message back to the hand muscles.

Answer: Mia pulls her hand away quickly.

Worked Example 2: Hearing your name

Question: Jordan hears his teacher call his name. How does the nervous system help?

Step 1: Jordan’s ears hear the sound.

Step 2: Nerves send the sound message to the brain.

Step 3: The brain understands that the teacher said, “Jordan.”

Step 4: The brain sends a message to turn his head and pay attention.

Answer: Jordan looks at his teacher.

Worked Example 3: Catching a ball

Question: A ball is thrown to Ana. How does her nervous system help her catch it?

Step 1: Ana’s eyes see the ball coming.

Step 2: Nerves send that message to her brain.

Step 3: Her brain figures out where the ball is going.

Step 4: Her brain sends messages through the spinal cord and nerves to move her arms and hands.

Answer: Ana lifts her hands and catches the ball.

Worked Example 4: Matching body parts to jobs

Question: Match each part to its job: brain, spinal cord, nerves.

• Control center
• Carries messages between brain and body
• Carry messages all around the body

Step 1: Think about what each part does.

• The brain is the control center.
• The spinal cord carries messages between the brain and body.
• The nerves carry messages all around the body.

Answer:

• Brain → Control center
• Spinal cord → Carries messages between brain and body
• Nerves → Carry messages all around the body

How to keep your nervous system healthy

Your nervous system is very important, so it is important to take care of it.

• Wear a helmet when riding a bike or scooter.
• Wear a seat belt in the car.
• Get enough sleep so your brain can rest.
• Eat healthy foods and drink water.
• Exercise and play safely.
• Tell an adult if you hit your head or get hurt badly.

Let’s remember

The nervous system is the body’s message system. It helps you sense, think, move, and stay safe.

The brain is the control center. The spinal cord connects the brain to the body. The nerves carry messages all around the body.

Every time you see, hear, touch, move, learn, or react, your nervous system is doing an important job.

The Digestive System

Your body needs food to grow, move, play, and learn. But first, your body has to break food down into tiny pieces it can use. The body system that does this job is called the digestive system.

The digestive system is like a food path inside your body. Food goes in your mouth, moves to your stomach, and then goes into your intestines. Each part has an important job.

1. The Mouth

Digestion begins in the mouth. When you take a bite of food, your teeth chew it. Chewing breaks food into smaller pieces. Your tongue helps move the food around in your mouth.

Your mouth also makes saliva. Saliva is the wet spit in your mouth. It helps soften food so it is easier to swallow. So in the mouth, food gets crushed, mashed, and mixed.

2. The Stomach

After you swallow, food travels down into your stomach. The stomach is like a stretchy bag. It squishes and mixes the food.

The stomach also uses strong juices to help break food down even more. These juices are called acids. The acids help turn the food into a mushy mixture. This makes it easier for your body to use the food later.

3. The Intestines

Next, the food moves into the intestines. The intestines are long, twisty tubes inside your body.

In the intestines, the food is broken down into tiny tiny parts called nutrients. Nutrients are the good parts of food that help your body. They help you grow, have energy, and stay healthy.

Your body takes in these tiny nutrients from the intestines. This is called absorbing the nutrients. That means the nutrients move into your body where they are needed.

How Food Moves Through the Digestive System

1. You eat food.
2. Your mouth chews and mixes it with saliva.
3. Your stomach squishes it and mixes it with acids.
4. Your intestines take the tiny nutrients from the food.
5. Your body uses those nutrients for energy, growth, and health.

Why Digestion Is Important

If your body did not digest food, the food would stay in big pieces. Your body cannot use big pieces of food very well. Digestion changes food into tiny parts your body can use.

That means the digestive system helps you:

• grow bigger,
• have energy to play,
• help your body stay strong,
• help your brain work while you learn.

Worked Example 1

Question: Where does digestion start?

Think: What part touches the food first and chews it?

Answer: Digestion starts in the mouth.

Why: The teeth chew the food, and saliva helps soften it.

Worked Example 2

Question: What does the stomach do to food?

Think: Does it chew, jump, or squish and mix?

Answer: The stomach squishes and mixes food.

Why: The stomach uses strong juices called acids to help break food down.

Worked Example 3

Question: What do the intestines take from food?

Think: What are the tiny good parts of food called?

Answer: The intestines take in nutrients.

Why: Nutrients are the tiny parts of food that help your body grow and have energy.

Worked Example 4

Question: Put these body parts in order: intestines, mouth, stomach.

Think: Where does food go first, next, and last?

Answer: Mouth  Stomach  Intestines

Why: Food is chewed in the mouth, mixed in the stomach, and nutrients are taken in by the intestines.

Easy Things to Remember

• Mouth: chew and soften
• Stomach: squish and mix
• Intestines: take in nutrients

You can remember it like this: Chew, squish, soak up.

Brief Summary

The digestive system helps your body use food. Food goes from the mouth to the stomach to the intestines. The mouth chews, the stomach mixes with acids, and the intestines take in nutrients that help you grow, move, and stay healthy.

Sleep is very important for our brains and bodies. When we sleep, we are not just "doing nothing." Sleep is a special time when the brain and body do important jobs.

This lesson will help you learn why sleep matters. You will learn how sleep helps us learn, grow, and feel better.

What is sleep?

Sleep is a time when your body rests and your brain keeps working in a helpful way. Your eyes close, your muscles relax, and your body becomes calm. But inside your head, your brain is still busy doing important jobs.

Sleep helps the brain.

Your brain helps you think, learn, remember, and pay attention. After a day of playing, reading, talking, and learning, your brain has a lot to sort out.

When you sleep, your brain helps save what you learned. It is like putting school papers into the right folder. Sleep helps your brain remember new songs, new words, and new ideas.

That means if you learn something today and then get a good night's sleep, your brain can help you remember it better tomorrow.

Sleep helps the body.

While you sleep, your body also does important work. It helps fix little hurts from the day. It helps your body heal and get ready for the next day.

Your body also grows during sleep. Sleep is a time when the body gets help to grow strong bones, strong muscles, and healthy skin.

Sleep helps us feel good.

When children get enough sleep, they often feel happier, calmer, and more ready to learn. They may have more energy to play and listen.

When children do not get enough sleep, they may feel tired, grumpy, or have trouble paying attention. It can be harder to remember things and make good choices.

What happens during the day and night?

• In the daytime, you learn, move, play, and use your body and brain.
• At night, sleep helps your brain remember and helps your body repair and grow.

So daytime and nighttime work together. Daytime is for doing. Nighttime is for helping your body and brain get ready to do more.

Signs that sleep is important

• You can pay attention better.
• You can remember better.
• Your body feels stronger.
• You may feel calmer and kinder.
• You have energy to learn and play.

Healthy sleep habits

There are simple ways to help your body get ready for sleep.

• Go to bed at about the same time each night.
• Have a calm bedtime routine, like brushing teeth and reading a book.
• Sleep in a quiet, cozy place.
• Rest your body and close your eyes.

Worked Example 1

Mia learned a new song at school. That night, she got a good night's sleep. The next day, she remembered more of the song.

Why did this happen?

It happened because sleep helped Mia's brain remember what she learned.

Worked Example 2

Jay played outside, ran, climbed, and jumped all day. At night, he slept well.

What did sleep help Jay's body do?

Sleep helped Jay's body rest, repair, and grow so he could be ready for the next day.

Worked Example 3

Lina went to bed very late. The next day, she felt tired and had trouble listening to her teacher.

What may have happened?

Lina may not have gotten enough sleep. Without enough sleep, it can be harder to pay attention and learn.

Worked Example 4

Two children are getting ready for a school day:

1. Noah slept well.
2. Eva did not sleep enough.

Who will most likely feel more ready to learn?

Noah will most likely feel more ready to learn because sleep helps the brain and body get ready for the day.

Let’s remember the big idea.

Sleep is not just quiet time. Sleep is working time for the brain and body. The brain uses sleep to help remember learning. The body uses sleep to repair and grow.

That is why sleep is a very important part of staying healthy.