The Human Body Reading Comprehension Lesson

The Major Body Systems

The human body is an incredible machine made up of many different systems that work together to keep you alive and healthy. Six of the most important systems are the muscular system, the respiratory system, the skeletal system, the digestive system, the circulatory system, and the nervous system. Each one has a specific job, and each one depends on the others to function properly.

The respiratory system takes in oxygen and releases carbon dioxide. Every time you breathe in, your lungs fill with air. Oxygen from the air passes into your bloodstream, and your blood carries it to every cell in your body. The circulatory system — your heart, arteries, and veins — is what pumps that oxygen-rich blood throughout your body. Your heart beats about 100,000 times a day without stopping.

The digestive system breaks down the food you eat so your body can use the nutrients for energy and growth. The nervous system — your brain, spinal cord, and nerves — controls everything your body does, from breathing and heartbeat to movement, thought, and sensation. All six systems communicate and cooperate constantly to keep you functioning.

Muscles and Bones

The human body contains about 640 muscles. Muscles are organized into three groups: voluntary muscles, involuntary muscles, and cardiac muscle. Voluntary muscles are the ones you control consciously — like the muscles in your arms and legs when you walk or throw a ball. Involuntary muscles work automatically without you thinking about them — like the muscles in your stomach that digest food.

Cardiac muscle is a special type that is found only in the heart. Like involuntary muscles, cardiac muscle never stops working, even while you sleep. It keeps your heart beating all day and all night for your entire life. Even during rest, your cardiac muscle is continuously pumping blood through your body.

The skeletal system gives your body its shape and structure. The human skeleton is made up of 206 bones, which are held together at joints by strong bands of tissue called ligaments. The skull protects the brain. The rib cage — made up of twelve pairs of ribs — protects the heart and lungs. The smallest bones in the body are found in the ear, while the strongest and longest bone is the femur, or thigh bone.

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