首页>英语角 > 听力 > 美音 > 课 程 > 科学 > 高二>What Is the Skeletal System?
Hi, I'm Jim Shields for About.com, and today I'm going to teach you about the skeletal system.  The skeletal system provides structure for the body. Because it is inside our bodies, the human skeletal system is called an endoskeleton, as opposed to the exoskeleton of a crustacean that is outside its body.Made up of about 206 bones, our skeleton not only supports the body and gives it shape, but it also protects the internal organs from damage. The skeletal system provides a rigid structure for the muscles to pull against, which makes movement possible.  There are two parts of the skeletal system: the axial skeleton and the appendicular skeleton. The axial skeleton includes the skull, spine, ribs and sternum. The appendicular skeleton includes bones of the the arms and legs, as well as the clavicle, pelvis and scapula. Bones themselves are less dense than you might think, and make up less than 20% of the body's mass.Even though they might seem like hard, dry objects, bones are actually dynamic, living tissue containing nerves and blood vessels, and the bones store vital minerals like calcium and phosphorus. Red blood cells and certain types of white blood cells are produced in the internal area of the bones where the soft tissue, called "bone marrow," resides.So remember, your skeletal system uses hundreds of bones working together to support the body, aid in movement and protect vital internal organs. The size and shape of each bone is determined by its role in the skeletal system. Thanks for watching. To learn more about biology, visit us on the web at About.com.
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