To put it mildly, the human body is a  complex structure. It is primarily composed of living cells, which work  together to form tissues, organs, and organ systems. Studying the structure of  the human body is a field unto itself – a science called anatomy.
            
            The human body can be separated into  several different organ systems, each responsible for performing specialized  roles and sustaining life.
            
            The integumentary system, made of the skin,  is our body’s largest organ. The skin acts as a protective sheath against  harmful microorganisms, heat and other environmental hazards.
            
            The body’s muscular system is divided into  skeletal muscles, which enable movement; cardiac muscles, which work to pump  blood in the heart; and smooth muscles, which perform involuntary processes  like digestion.
            
            Skeletal muscles are attached to the bones  of the skeletal system. Our skeleton provides a sturdy framework for the body,  protects our delicate insides, and produces various blood cells.
            
            Other systems include the digestive system,  which absorbs and converts food into energy and building material; the circulatory  system, which works with the respiratory system to provide oxygen for cellular  activities; the immune and lymphatic systems, which protect against harmful  particles; and the reproductive system, which ensures the continued survival of  the human race.
            
            Lastly, the nervous system controls all of  the aforementioned processes, ensuring that all processes contribute to  homeostasis and continued living.
            
            This
            
             human body labeled
            
            diagram is a useful resource to better visualize the divisions within the human  body and relate them to the body’s various processes.
           
Here is a list of some external body parts and their functions: