Heart, Lungs and a Healthy Lifestyle

Your heart is busy even when you are asleep. It pushes blood around the circulatory system, your body's transport system. The other parts are blood and the tubes called blood vessels.

A muscle inside your chest

Your heart is a hollow, muscular organ about your fist's size. It sits between your lungs, behind your breastbone. About two-thirds of it lies left of the middle of your chest. Your ribs help protect it. Its shape is closer to a rounded cone than a heart drawn on a greeting card.

The heart's walls contract, which means they squeeze. That squeeze pushes blood out. The walls then relax, and the heart fills again. One squeeze and relaxation makes one heartbeat. Flaps called valves stop blood from flowing backward. Their closing makes the "lub-dub" sound heard through a stethoscope.

Your heart works automatically. You do not decide to start each beat. It also relaxes between squeezes, even though it keeps beating throughout your life. Its rate changes: running, excitement, and fear can speed it up. Rest and sleep usually slow it down.

Two sides with two jobs

A wall divides the heart into a right and left side. The right side sends blood to the lungs to collect oxygen. The left side sends blood from the lungs around the body. The dividing wall keeps these flows separate.

The left side has thicker muscle. It needs a stronger push to send blood to distant body parts. The right side sends blood the short distance to the lungs. The heart's structure fits the work it does.

On a picture of someone facing you, their right appears on your left. Heart labels always mean the person's own right and left. Imagine standing in that person's place before reading the labels.

Count a day's beats

Imagine a steady rate of 70 beats each minute. An hour has 60 minutes:

A day has 24 hours:

That is about 100,000 beats in a day. A real heart changes speed during the day, so this is a worked estimate at one steady rate.

The heart pumps blood; it does not make the blood cells. Soft tissue inside bones, called bone marrow, makes them. The lungs add oxygen, and the kidneys remove certain wastes.

Blood needs a route to reach your muscles, skin, and organs. Arteries, capillaries, and veins form that route. Their different walls help them do different jobs.

Match the tube to its job

Each heartbeat sends a surge into the arteries. Their walls stretch with that surge. You can feel it as a pulse where an artery lies near your skin.

Arteries branch into smaller tubes until blood reaches capillaries. These are much thinner than a hair. Oxygen, nutrients, and water pass through their thin walls to nearby cells. Carbon dioxide and other wastes pass into the blood. Capillaries join the smallest arteries to the smallest veins.

Blood returns in veins under lower pressure. Many veins have valves, especially in your arms and legs. These flaps stop backward flow. When you walk, leg muscles squeeze the veins and help push blood toward your heart.

Follow a trip to your hand

Start with the heart's push. Blood leaves in an artery. Smaller arteries carry it along your arm. In your hand's capillaries, useful substances pass to cells. Veins then carry blood back up your arm to the heart.

The vessel order is heart → arteries → capillaries → veins → heart.

Direction gives the name

Remember A for artery, A for away. An artery is named by where it takes blood, not how much oxygen the blood holds. The artery to the lungs carries oxygen-poor blood away from the heart. Veins from the lungs bring oxygen-rich blood toward the heart.

Diagrams often use blue for oxygen-poor blood and red for oxygen-rich blood. Real blood is always red: darker with less oxygen, brighter with more. Veins can look blue through skin because of how light travels through skin.

Your blood returns to the heart between visiting the lungs and the body. This makes two linked loops, called double circulation. Blood passes through the heart twice during one full trip.

Trace both loops

The lung loop runs from the right side of the heart to the lungs, then to the left side. In the lungs, blood gains oxygen and gives up carbon dioxide.

The body loop runs from the left side to the body, then to the right side. In body capillaries, cells take oxygen and nutrients. They pass carbon dioxide and other wastes into the blood.

Follow blood leaving a toe:

1. Veins carry it toward the right side of the heart.
2. The right side pumps it to the lungs.
3. It collects oxygen and loses carbon dioxide there.
4. It returns to the left side of the heart.
5. The left side pumps it through arteries toward the toe.
6. It reaches the toe's capillaries and delivers oxygen again.

The blood keeps circulating. Your body uses what it carries, without using up the blood on each trip. Blood pressure falls as blood travels through the lungs. The return to the heart gives it another strong push for the body trip. Blood moves faster during exercise. The time for a trip varies; roughly a minute at rest gives a sense of its speed.

Mammals and birds also have two loops, with one through the lungs. Fish have hearts and vessels too, but collect oxygen through gills.

Choose a useful model

A model helps you study something hidden. Each model shows some features and leaves others out.

Suppose you want to explain a pulse. A squeeze pump shows a surge better than a still picture. To explain both loops, a clear arrow diagram may work better than a single loop of tubing.

A useful judgment names the feature and gives a reason: "The pump shows a surge when squeezed. It misses the lung trip because it has only one loop." More detail does not always make a model better for the question you are studying.

Blood looks like one red liquid, but it is a mixture. Cells and tiny cell pieces float in a watery liquid called plasma. Each part has its own job.

Four parts working together

Plasma is pale yellow and makes up about 55% of blood. Most of it is water. It carries dissolved nutrients such as glucose, salts, hormones, and wastes. Most carbon dioxide travels in the plasma in a changed, dissolved form.

Red blood cells are tiny disks, thinner in the middle. They contain hemoglobin, the red substance that picks up oxygen in the lungs. It releases oxygen where the body needs it. Red blood cells carry nearly all the oxygen in blood. They are very numerous: a tiny cubic millimeter of blood holds about 4 to 6 million.

White blood cells are larger and much less common. Some swallow germs. Others make antibodies that help fight particular germs. Their number can rise during an infection.

Platelets are small pieces of cells. At a cut, they stick together and help form a clot. This plug slows and stops bleeding. On the skin, the clot can dry into a scab. New skin grows beneath it.

Picture a scraped knee

First, skin has been broken, leaving an opening. Platelets help plug the damage so less blood escapes. White blood cells fight germs that enter. These are different kinds of protection: sealing the opening and attacking germs. Red blood cells keep carrying oxygen; fighting germs is the white cells' job.

Blood changes as you grow

Your bone marrow keeps replacing blood cells. A red blood cell lasts about 120 days, or four months. Millions of new blood cells are made each second.

The amount of blood depends on body size. An adult has about 5 liters, around 1.3 gallons. A child weighing 35 kilograms, about 77 pounds, has roughly 2.5 liters. Growing bodies need more blood to reach more tissue.

A muscle cell needs supplies even when it is far from your stomach and lungs. Blood links those organs with the cells that need their supplies.

Pick up, deliver, collect

Digestion breaks food into tiny nutrients. Glucose is one of these nutrients, a kind of sugar. Nutrients pass through the small intestine's wall into blood. Water enters the blood through the intestines too. Whole pieces of food do not travel through your blood vessels.

Oxygen follows a different route. It passes from air deep inside the lungs into the blood. Red blood cells carry it away. At body capillaries, oxygen, glucose, and water pass to nearby cells.

Cells such as muscle cells use glucose and oxygen to release energy. This is respiration. It produces carbon dioxide and water. The energy supports movement, warmth, growth, and repair. Food stores energy; oxygen helps cells release it.

Blood collects carbon dioxide from the cells and takes it to the lungs. You breathe it out. Blood carries other waste, such as urea, to the kidneys. The kidneys remove it from blood and make urine.

Follow a slice of bread

Imagine eating bread before a run. Track the supplies step by step:

1. Digestion breaks down the bread's starch into glucose.
2. Glucose enters capillaries in the small intestine's wall.
3. Blood carries it onward through the circulation.
4. Blood also collects oxygen during its trip through the lungs.
5. Blood reaches capillaries beside a leg muscle.
6. Glucose and oxygen pass into muscle cells, where respiration releases energy.
7. Carbon dioxide enters the blood and travels to the lungs to leave your body.

The heart keeps supplies moving. The lungs add oxygen. The digestive system supplies nutrients and water. The kidneys remove certain wastes. A problem in one system can affect the others because they depend on these shared routes.

More cargo in the same flow

Blood spreads heat from busy muscles and organs around your body. This helps keep body temperature near 37 °C, or 98.6 °F. It also carries hormones, chemical messengers that help control changes such as growth. White blood cells and platelets travel in the same flow to where they are needed.

Air and food both enter near your face, but they take different routes inside. Air travels through branching tubes to your two lungs.

Follow a breath inward

The route is nose or mouth → throat → windpipe → bronchi → smaller tubes inside the lungs. The windpipe's science name is trachea. It splits into two main tubes called bronchi. One tube is a bronchus. Each enters one lung and branches into smaller tubes, like an upside-down tree.

The lungs are soft, spongy organs in your chest. They contain many tiny air spaces and blood vessels. They are not two empty bags. Your left lung is slightly smaller, leaving room for the heart. Your ribs protect both lungs and the heart. The diaphragm is a sheet of muscle below the lungs.

Rings of stiff cartilage help hold the windpipe open. Its wall needs support so that air can keep moving through it.

Clean the air on its way

Nose hairs trap some larger particles. Sticky mucus catches dust and germs along the airways. Tiny moving hairs called cilia sweep that mucus toward your throat. You swallow it or cough it out. The nose also warms and moistens incoming air.

Picture a dusty speck entering your nose. It can stick to mucus before reaching deep into a lung. Cilia move the mucus upward, carrying the trapped speck with it. Mucus traps; cilia move. They work together, but their jobs are different.

Keep food on its own route

Food passes from the throat into the food pipe toward the stomach. A flap called the epiglottis helps cover the windpipe entrance when you swallow. This helps direct food away from the airways.

When a little drink goes "down the wrong way," coughing helps clear it from the airway.

Take a normal breath and notice your chest move. Your lungs stretch and shrink as the space around them changes. The diaphragm and rib muscles cause that change.

Make room for air

Your diaphragm is a dome-shaped muscle under the lungs. When it flattens, the chest has more space. The lungs expand with that space, and air enters. The lungs do not pull air in by squeezing like a muscle pump.

When you breathe out quietly, the diaphragm and rib muscles relax. The diaphragm returns toward its dome shape. The lungs spring back toward their smaller size, pushing air out. Bigger chest space means breathing in; smaller space means breathing out.

Place your hands on your lower ribs during a normal breath. You can feel them move outward and then inward. Your brain controls breathing automatically, including while you sleep. You can change a breath briefly to sing or blow out a candle.

Understand a model lung

Imagine a prepared bottle model. A balloon hangs inside from a straw. A stretchy sheet seals the bottle's open bottom.

• The bottle represents the chest space.
• The balloon represents a lung.
• The straw represents the windpipe.
• The stretchy sheet represents the diaphragm.

Pull the sheet down. Space inside the bottle grows, and air enters the balloon through the straw. Push it up. Space gets smaller, and air leaves the balloon.

The model shows how changing space moves air. Its stiff bottle cannot show moving ribs. One balloon leaves out the second lung. The sheet also needs a hand to move it, while your diaphragm contracts as a muscle. No part shows oxygen entering blood.

Count a whole breath

One breath includes both breathing in and breathing out. Breathing rate counts these complete breaths each minute. It varies between people and rises during exercise. Count a complete in-and-out cycle once, so you do not accidentally double the result.

Both the air you breathe in and the air you breathe out are mixtures. Your lungs change some of the mixture as blood passes close to air deep inside them.

Compare the gases

These are approximate values. Breathed-out air still has plenty of oxygen. It is not pure carbon dioxide. Both mixtures are mostly nitrogen, which your body does not use from the air.

Oxygen passes from lung air into blood. Carbon dioxide passes from blood into lung air. Blood then returns to the left side of the heart, which pumps it toward the body. Oxygen reaches muscles through blood, without traveling there directly through an airway.

Breathed-out air is also warmer and wetter. On a cold mirror, its water vapor cools into tiny droplets. The mist shows that a breath contains water vapor.

Look for evidence

A teacher can compare ordinary air with breathed-out air using limewater. Breathed-out air makes it cloudy faster because it has more carbon dioxide. This is a teacher-led demonstration: blow outward through the straw and never suck up the liquid.

The change from 0.04% to 4% is large. There is about 100 times as much carbon dioxide in breathed-out air. Oxygen falls from about 21% to 16%, so some oxygen remains after the body takes what it needs.

Breathing and respiration do different jobs

Breathing moves air into and out of your lungs. Respiration releases energy inside cells. In muscle cells, glucose and oxygen are used, making carbon dioxide and water.

During a run, your muscle cells need to release more energy. Breathing brings fresh air into the lungs. Blood carries more oxygen to working muscles and brings carbon dioxide back. Your heartbeat and breathing speed up together because transport and air movement must keep up with those cells.

You can count your heartbeats by feeling an artery near your skin. The small surge you feel is your pulse. Pulse rate gives the number of beats each minute, in beats per minute, or bpm.

Find a steady count

Sit quietly for a few minutes first. Place your first two fingertips gently on your inner wrist, below the thumb's base. Shift them slightly until you feel a beat. Use your fingers, because your thumb has a pulse of its own.

You can also feel a pulse beside the windpipe in your neck. Touch gently on one side only. The wrist is convenient for the investigation.

Count beats for 15 seconds, then multiply by four. There are four 15-second periods in one minute. For example, 19 beats in 15 seconds gives:

The rate is 76 bpm. For a 30-second count, multiply by two. A count of 37 gives:

That is 74 bpm. Keep the counting time beside the count, so you use the right multiplier.

Make the measurement better

A missed beat matters more in a short count. Missing one during 15 seconds makes the final rate 4 bpm too low. A longer count reduces this effect. At rest, you can count for a full minute with no multiplication. Just after exercise, a short count is useful because your pulse starts slowing quickly.

Repeat resting measurements under the same calm conditions. To find their mean, add the rates and divide by the number of rates. For 76, 72, and 74 bpm:

The mean is 74 bpm. Repeating helps reveal a miscount, but keep checking your method too.

Rates can change

Many children your age have resting rates around 70–100 bpm. Rates differ between people and change with exercise, excitement, fever, and caffeine. Adults often have resting rates around 60–100 bpm. Trained athletes may have lower resting rates. A single comparison with a friend is not a fitness test.

A stethoscope lets someone listen to the heart. A heart-rate monitor counts beats electronically. You can also measure breathing: a partner counts complete breaths for 30 seconds, then doubles the count. Nine breaths gives 18 breaths per minute. Let your breathing stay natural while your partner counts.

A pulse investigation needs a clear question and careful timing. You might ask, "How does one minute of jumping jacks change my pulse?" Predict a rise because working muscles need more oxygen and glucose.

Plan a fair comparison

The thing you change is the independent variable. The thing you measure is the dependent variable. Things you keep the same are control variables.

If you compare exercise durations, change only the duration. Keep the person, activity, speed, resting time, and counting method the same. Changing the activity as well would make it hard to tell what caused a difference.

Choose a safe activity with enough room. Stop if you feel dizzy, sick, or chest pain, and tell an adult. Follow your doctor's and teacher's advice about any health condition.

Collect and organize results

Sit quietly for five minutes and measure your resting pulse. Do jumping jacks for one minute. Measure immediately, then after each minute of rest. Recovery time is the time taken to return to the resting rate.

Sam counted for 15 seconds each time:

Each rate comes from multiplying the count by four. The rise is:

Sam's pulse rose by 68 bpm and returned to its starting rate after four minutes.

Show and explain the pattern

For a recovery line graph, put time after exercise on the horizontal axis. Put pulse rate on the vertical axis. Label both axes with units. Plot 0 minutes as the immediate after-exercise rate. Show the resting rate separately as a comparison line.

A useful conclusion gives evidence and a reason: "Sam's pulse rose from 76 to 144 bpm, then returned to 76 bpm after four minutes. Working muscles needed more oxygen and glucose, so the heart pumped faster."

Repeat the investigation after full rest. If a result is very different, check the count and method. Do not quietly erase it. Measure immediately after exercise each time, because waiting lets pulse fall. When comparing people, consider both the rise from their own resting rate and recovery time. One high reading alone cannot rank everyone's fitness.

When you run, your leg muscles release energy faster. They need more oxygen and glucose and make more carbon dioxide and heat. Your heart and lungs respond to that extra demand.

What changes right away?

Your heart beats faster and pumps more blood with each beat. You breathe faster and more deeply. More supplies reach working muscles, and more carbon dioxide returns to the lungs.

You also get warm. More blood flows near your skin's surface to lose heat. Sweat cools you as it dries. Your muscles may tire, and you may feel out of breath. At rest, your heart still supplies your organs; movement muscles simply need less energy than during exercise.

What changes with regular activity?

Over weeks and months, activity makes the heart stronger. A stronger heart can pump more blood in each beat. It can then supply a resting body with fewer beats. Breathing muscles, bones, and other muscles strengthen too. Activity can support sleep and mood.

Different activities build different abilities:

Moderate activity warms you and makes breathing harder, but you can still talk. Brisk walking is an example. During vigorous activity, you can say only a few words before pausing for breath. Fast running often feels like this.

Fit movement into your day

The CDC advises ages 6–17 to get at least 60 minutes of moderate to vigorous activity each day. Vigorous activity and muscle- and bone-strengthening activity should be included on at least three days each week. WHO advice for ages 5–17 uses an average of at least 60 minutes a day across the week.

Short bursts add up. Maya cycles for 20 minutes, plays tag for 25, and walks the dog briskly for 15:

That makes 60 active minutes. You can build activity into travel and play. Starting with small amounts is useful too, and movement breaks help during long periods of sitting.

Your heart needs a steady supply of nutrients, just like other muscles. A balanced diet provides different foods in useful amounts. You need enough food to grow, learn, and be active.

Give each nutrient a job

Choose vegetables and fruit, grains, protein foods, calcium-rich foods, small amounts of fats, and water. Whole grains add fiber. Beans, eggs, fish, chicken, and nuts are examples of protein foods.

Iron is a mineral needed to make hemoglobin, which carries oxygen. This is one link between what you eat and what your blood can do.

Care for your blood vessels

Eating a lot of saturated fat over time can contribute to fatty buildup inside arteries. Narrower, stiffer arteries make blood flow harder. If an artery feeding heart muscle becomes blocked, a heart attack can happen. Butter and fatty meats contain saturated fat. Plant oils, nuts, and fish provide healthier fat choices. Your body still needs some fat.

Too much salt can raise blood pressure, the push of blood against vessel walls. High pressure can damage vessels and make the heart work harder.

Lots of added sugar can cause tooth decay. Regularly taking in more energy than your body uses also leads to stored body fat. The American Heart Association advises children to limit added sugar to no more than 25 grams a day, about six teaspoons.

A soda label showing 39 grams of sugar means roughly ten teaspoons. One teaspoon holds about four grams:

That is more than the advised daily added-sugar limit in one drink.

Compare whole meals

A whole-grain chicken-and-salad wrap, apple, and water gives grains, protein, vegetables, fruit, and a drink without added sugar. A burger, fries, and soda offers less variety and often more salt, saturated fat, and sugar. Compare the whole meal and your usual eating pattern. A treat sometimes can fit alongside varied everyday meals.

Smoke carries harmful substances into the same airways that bring you oxygen. Smoking damages the lungs, heart, and blood vessels. Breathing someone else's smoke can harm you too.

Three substances, different harms

Tobacco smoke contains more than 7,000 chemicals. At least 250 are harmful, and at least 69 can cause cancer. Three substances help explain several of the harms.

Nicotine is an addictive drug. Addiction means your brain and body begin to crave a substance, making stopping hard. Nicotine raises heart rate and narrows blood vessels, increasing blood pressure.

Tar is a sticky mixture that coats airways and damages cilia. Cilia normally sweep mucus and trapped dirt toward the throat. When they are damaged, mucus builds up. Coughing and chest infections become more likely. Over many years, smoking can cause serious lung disease and lung cancer.

Carbon monoxide is a poisonous gas. It attaches to hemoglobin and reduces the space available for oxygen. Blood then carries less oxygen, so the heart works harder to supply the body. This helps explain why smoking can make exercise harder.

Smoking also damages artery linings and encourages fatty buildup. This raises the risk of heart attacks and strokes. Its harm reaches beyond the lungs.

Smoke affects people nearby

Secondhand smoke is breathed in by someone near a smoker. It contains harmful chemicals too. Children exposed to it have more chest infections and asthma attacks. Keeping homes and cars smoke-free protects the people sharing that space.

Vaping is not breathing plain water

Vapes heat liquid into an aerosol, a mist of tiny particles that is breathed in. Most contain nicotine, and the aerosol can contain other harmful chemicals. A sweet smell or fruit flavor does not make it safe.

Nicotine can harm a developing brain, which continues developing into the mid-twenties. Tobacco and nicotine products are unsafe for young people. Nearly nine in ten adults who smoke daily began by age 18. Many countries restrict sales to young people because starting early can lead to a lasting addiction.

If someone offers you a vape, a short reply can be enough: "No, thanks." You can move away and speak with a trusted adult if the pressure continues.

A drug changes how your body or mind works. Medicines are drugs. So are caffeine, nicotine, and alcohol. A substance being familiar does not tell you whether it is safe to take.

Medicines need the right use

Medicines can prevent or treat illness. The wrong medicine, too much, or doses taken too close together can harm you. Take medicine only when a trusted adult, such as a caregiver, doctor, or school nurse, gives it to you. Follow its instructions and never take someone else's medicine.

Imagine a friend offers you their tablets for a cough. Even if your cough sounds similar, the tablets may not suit you. Ask your trusted adult to help instead of sharing medicines.

Caffeine and alcohol work differently

Caffeine is a stimulant. It can speed up your heart, make you feel alert or restless, and disturb sleep. It occurs in coffee, tea, cola, energy drinks, and chocolate. Energy drinks can contain high caffeine levels. Many also have lots of sugar, but sugar-free energy drinks still contain caffeine. They are not recommended for children.

Alcohol is a depressant. It slows brain activity and harms balance, reaction time, speech, and judgment. Large amounts can dangerously slow breathing and cause alcohol poisoning. Heavy drinking over years can damage the liver, heart, and brain. Children's developing bodies are especially vulnerable.

Unknown drugs and inhalants

Other drugs can change heart rate, breathing, mood, and thinking. Many are addictive. Drugs from unregulated sellers may contain unexpected substances or much stronger amounts than expected. Laws differ between places and substances; a legal product can still be harmful.

Solvents and inhalants include fumes from some glues, aerosol sprays, and lighter gas. Breathing these in deliberately can cause a dangerous heart rhythm, even the first time. Use household products only for their labeled purpose in fresh air.

Make a plan for pressure

You can say, "No, thanks," leave, and find a trusted adult. You do not owe someone a long explanation. If someone becomes very unwell after taking a substance, get an adult immediately or call the emergency number where you live.

A plant source does not make a drug harmless. Tobacco comes from a plant, yet nicotine is addictive and smoke harms your heart and lungs.