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Name Lesson 3 Summary Use with pp. 46–49 Lesson 3: How do organs work together? Vocabulary organ system a group of organs and tissues that work together to carry out a life process Organ Systems Organ Systems Work Together Cells work together in tissues. Tissues work together in organs. Organs work together as part of an organ system. For example, the mouth, stomach, intestines, and other organs work together to digest food. The muscle and skeletal systems work together to move your body. Muscles work in pairs to move bones. Try this. Hold your arm out straight in front of you. Bend your elbow. The muscle on the bottom of your arm relaxes. The muscle on top of your upper arm tightens. This pulls on the bone of your upper arm and makes your elbow bend. The opposite happens when you stretch your arm. The bottom of your upper arm tightens. The top of your arm relaxes. Bones Form a System Each bone is an organ. There are about 200 bones in the skeletal system. This organ system gives your body support. The skeletal system also protects important organs. The skull is made of bones that protect your brain. The rib cage is made of bones that protect your lungs and heart. Muscles Work as a System Your organ systems work together too. For example, your nervous system controls how your muscles move bones. Nerves carry signals from your brain and spinal cord to your muscles. Without nerves, your muscles would never move. Some organs work for more than one organ system. For example, muscles don’t just work with bones. Muscles in your heart push blood through your blood vessels. © Pearson Education, Inc. 5 Muscles are organs. They work together to move your body. There are about 640 muscles that you control. When you run, your brain tells your muscles how to work together. Other muscles work by themselves. When you shiver, muscles work to warm the body. You do not have to think about shivering. It happens without your thinking about it. Other Systems Work Together 14 Chapter 2, Lesson 3 Summary Quick Study Name Lesson 3 Checkpoint Use with pp. 46–49 Lesson 3 Checkpoint 1. How many bones make up the skeletal system? 2. List some organ systems and describe their jobs. © Pearson Education, Inc. 5 3. How do muscles work in pairs to move a bone? Quick Study Chapter 2, Lesson 3 Checkpoint 15