26 The Human Body-Low

The Human Body Written by Kira Freed

Introduction Your body has many systems that work together to keep you alive. The systems are working all the time. They all need to stay healthy to do their jobs. Do You Know? See what you know before you read this book. What do you know about each of these body systems? skeletal system muscular system nervous system respiratory system circulatory system digestive system excretory system reproductive system endocrine system immune system

Every minute of your life, your heart pumps blood. Messages move to and from your brain. Your lungs carry oxygen to cells. Your body kills bad germs and gets rid of waste products. It also does many more jobs—even while you sleep! In this book, you will learn about seven important body systems. As you read, think about all the jobs each body system does to keep you alive and healthy.

The Skeletal System The bones of your skeletal system support the rest of your body. Bones also protect your organs and help you move. Your spine the main support, has twenty-six bones. Your skull protects your brain from getting hurt. Your ribs protect your heart and lungs. Your pelvis helps to protect the organs in your belly.

Long, strong bones support your arms and legs. Your hands, wrists, feet, and ankles have many small bones. Each of the 206 bones in your body has a special job. Did you realize your bones are alive? Bones are made of living cells. This is why bones grow. Bone marrow in the middle of bones makes new blood cells. Do You Know? Can you guess where the smallest bones in your body are? They're in your middle ears! Three tiny bones carry sounds from your eardrums to your inner ears.

The Muscular System The muscular system works with the skeletal system so you can move. Your muscles can contract (become shorter and tighter) or relax (become longer and looser.) Your body has three kinds of muscles. Skeletal muscles connect to bones. When you run, smile, or pick up a pencil, your skeletal muscles are working.