Body systems are tissues, structures, and organs that are organized by what they do, not by their location in the body. Each body system depends on the others to do its job effectively. The body systems covered in this lesson are as follows: the musculoskeletal system, the circulatory system, the respiratory system, the nervous system, the the digestive and excretory systems, and the endocrine system. These systems are common to both males and females. One other system, the reproductive system, is different for each sex.

The musculoskeletal (MUHS cyoo loh SKEL eh tuhl) system is made up of two subsystems: the muscular system and the skeletal system. Together, the skeletal and muscular systems support and move the body and protect soft internal organs.

The Skeletal System The skeletal system is the framework of bones and the tissues connecting the bones. The skeletal system in adults is made up of 206 bones. Its main functions are to support your body protect vital organs like the brain produce blood cells serve as a storage area for minerals Joints are places where two bones meet. Some joints move, while others, like those in the skull, do not move. Moveable joints make the skeleton flexible. Without them, movement would be impossible. Ligaments hold the bones together at the joint. Tendons are the tissues that connect muscles to bones.   The Muscular System The muscular system is made up of tissues that work with the skeletal system to control movement of the body. Some muscles, like the ones in your arms and legs, are voluntary. Voluntary means that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines, and other organs, are involuntary. Involuntary means that they are controlled automatically by the nervous system and hormones. You may not even realize when they are at work.