The Human Body

The human body is like a wonderful machine. However, no machine can do the things your body can do. All body parts work together to help keep you healthy.

Your body has more than 200 bones. It also has more than 600 muscles. Bones and muscles give your body support. As a result, you walk, sit, and stand. These actions are also under the control of your nervous system.

Body Parts

A cell is the smallest living part of your body. Cells have different shapes and sizes. Each kind of cell has a different job to do. Brain cells do one job while skin cells do another job.

Cells in parts of your body form tissues. A tissue is a group of cells that work together to do a special job. All body parts are made of tissues. Bone and muscle are

8

types of tissues.

An organ is a body part made of different kinds of tissues. Your eye is an organ. Your heart is an organ. What other body organs can you name?

Organs in your body form a body system. A body system is a group of organs that work together to do a certain job. Your lungs and air passages are part of a body system.

Bones

Bones form a frame that supports your body. They are also place of attachment for muscles. The bony frame in your body is called a skeleton. Bones of the skeleton protect many of your body organs. Skull bones protect your brain. Ribs protect your heart and lungs. Your back bones protect your spinal cord.

Blood cells are made inside the long bones in your body. These bones contain marrow. Bone marrow is soft tissue in the center of long bones.

Bones are joined to other bones. A joint is the place where two bones meet. Joints allow your body to move in certain ways. The joint at your knee allows you to bend your leg. Joints in your hand allow you to bend your fingers. Joints in your back allow you to bend at the waist.

Muscles

Muscles are a type of tissue that helps your body in many ways. All muscles in the body are a part of the muscular system.

9

Muscles help you do many tasks. You can control muscles that help you walk, run, and talk. However, you cannot control other muscles, such as your heart muscle. Your heart muscle pumps blood throughout your body. Muscles around your ribs help you breathe. Muscles in your stomach help to digest food.

Many muscles work in pairs. When one muscle contracts, the other one relaxes. To contract means to become smaller. When a muscle contracts, it becomes shorter and thicker. The two ends of the muscle come closer together. When a muscle contracts, it pulls on the bone to which it is attached. This will cause the bone to move. When a muscle relaxes, it stretches and becomes longer.

Skin

Skin is the largest organ in the body. Skin helps control body temperature. When the body is warm, water is lost through the skin in the form of sweat. As water is lost, heat escapes from the body. Sweating helps keep the body cool. When the body is cool, less heat is lost through the skin. This helps keep the body warm.

Skin helps protect the body against germs. Broken skin lets germs enter the body. It is important to wash broken skin to get rid of dirt and germs.

Skin on all parts of your body is made of two layers of tissue. Each layer is made of special cells.

10

Nerves and Sense Organs

The human body contains millions of neurons. Neurons are nerve cells that help control body activities. They are a part of the nervous system.

The brain is a mass of neurons found within the skull. There are billions of neurons in the brain. The spinal cord is a long column of neurons. It extends down the back from the base of the brain.

Neurons in the brain, spinal cord, and throughout the body form a network. This network carries messages between the brain and the entire body to help the body work.

Sense organs are also part of the nervous system. The five senses are seeing, hearing, touching, tasting, and smelling Messages travel through neurons from the sense organs to the brain. For example, messages from the tongue travel to the brain. This lets you know the taste of foods.

Your senses help protect your health. Your sense of hearing warns you when a car is coming. Your sense of smell can warn you of smoke from a fire. How can your other senses protect you?

Energy and Transport

Certain parts of a car work together to help the car use energy. The energy moves throughout the engine to move the car. Other parts work together to help get rid of wastes from the car. In much the same way, your body needs energy to work. Some body systems help you use energy.

11

Others help get rid of body wastes.

Digestion

The food you eat is not in a form your body cells can use. It must be changed to supply your body with energy. All cells need energy in order to function. Digestion is the process of changing food in your body. The food is changed into materials that can enter your bloodstream. Your blood carries these digested food materials to a body cells.

Within the cells, oxygen combines with these food materials. This causes energy to be released. This energy is used to help your body do many things.

Circulation

The heart is a muscle that pumps blood. It is the main organ of circulation. Circulation is the transport of blood throughout your body. Blood flows throughout your body in blood vessels. The heart and blood vessels make up your circulatory system.

There are three kinds of blood vessels. Arteries are blood vessels that carry blood away from your heart. Most arteries carry oxygen and digested food to cells in your body. Capillaries are very small blood vessels that connect arteries to veins. Veins are blood vessels that return blood to your heart.

Respiration

Without oxygen, body cells can live only a few

12

minutes. The air you breathe contains oxygen. Your body gets oxygen when you inhale. This happens through a process called respiration. Respiration is the exchange of gases within the body.

The circulatory system helps with respiration. Your blood picks up oxygen from your lungs. In this way, oxygen is carried throughout your body. As your body cells use oxygen, a waste gas called carbon dioxide is produced. Carbon dioxide is carried in veins back to your heart and then back to your lungs. Carbon dioxide is removed from your lungs when you exhale.

The respiratory system helps keep you healthy. When you inhale, air is warmed by blood vessels inside your nose. Mucus inside your nose traps dirt that may be in the air. Mucus is a liquid that moistens and protects some body parts. Your nose and throat contain mucus. Sneezing helps your body get rid of dirt and mucus trapped in the airway.

All body systems work together. You can take actions to protect them and keep them healthy. Protect your respiratory system. Do not smoke. Smoking harms your lungs. It is a leading cause of lung cancer.

1 Learn the following life skills:

• Help keep your bones strong by eating dairy

products and by exercising.

• Wash all cuts to keep germs from entering your

body.

• Get plenty of sleep and rest to keep your nervous

13

system healthy.

• Eat fruits and vegetables for healthy digestion.

• Help keep your respiratory system healthy by not smoking.

2 Put a special question to the italicized words:

1 The body is made up of cells, tissues, organs, and

systems.

2 Bones give the body support and help protect some body organs.

3 Many different kinds of muscles help the body move.

4 The skin helps control body temperature and keep germs from entering the body.

5 Nerves and sense organs help the body respond to its environment.

6 The digestive system helps the body use food.

7 Blood moves through the body in arteries, capillaries, and veins.

8 The respiratory system helps the cells in the body exchange gases.

3 Complete each sentence with the correct word:

bone marrow joint respiration

capillaries mucus skeleton

circulation neuron tissue

digestion organ veins

14

1 A___is a part of the body where two bones

meet.

2 The heart is an example of an__ .

3 The process of changing food in the body is called__ .

4 The___is a bony frame that supports the body.

5 ___is the soft tissue in the center of long

bones.

6 ___are nerve cells.

7 The heart is the main organ of­­___ .

8 Breaching is a part of____ .

9 Different kinds of cells work together to foi type of___

10 Small blood vessels that connect arteries to are called___ .

4 Answer the questions:

1 How do cells and tissues differ?

2 How are bones important to your health?

3 How can you help keep your bones healthy?

4 How does your heart muscle keep you alive?

5 How does your skin help keep you healthy?

6 Why should you wash your skin if you get a cut?

7 How can a sense organ help protect you?

8 What is the purpose of digestion in the body?

9 How are arteries and veins different?

10 How does your respiratory system help keep you healthy?

5 Use the life skills from this chapter to respond to the following questions:

15

Situation: You have just learned about ways to keep your

bones strong. You are in the cafeteria line at university. You have a choice of milk, chocolate cake, cheese, potato chips, soda pop, and yogurt.

1 What foods would you choose for healthy bones?

2 What other foods might keep your bones healthy?

6 Think about it:

1 Why is the heart considered an organ?

2 Why is calcium important to the body?

3 Why does food need to be digested?

4 Why are arteries important?

5 What can you do to lower your risks of developing

lung cancer?

7 Describe two ways each of your sense organs help keep you healthy. Ask others for ways they believe their sense organs help them stay healthy.