An organ is a collection of tissues joined in a structural unit to serve a common function. Many organs are composed of a major tissue that performs the organ’s main function, as well as other tissues that play supporting roles.
The human body contains five organs that are considered vital for survival. They are the heart, brain, kidneys, liver, and lungs. If any of these five organs stops functioning, death of the organism is imminent without medical intervention.
Functionally related organs often cooperate to form whole organ systems. There are 11 major organ systems in the human organism. They are the integumentary, skeletal, muscular, nervous, endocrine, cardiovascular, lymphatic, respiratory, digestive, urinary, and reproductive systems. Only the reproductive system varies significantly between males and females.
