Organ Systems :  Organisms are composed of organ systems. Each organ system is made up of several different organs. For example, the digestive system is composed of several organs: the mouth, tongue, salivary glands, pharynx, esophagus, stomach, intestines, liver, and pancreas.

Organs are composed of two or more of the primary types of tissue: epithelial, connective, nerve, or muscle tissue. Tissues, in turn, are composed of groups of similar cells that perform specialized functions.

The human body is composed of various systems: integumentary system - which covers and protects the body; skeletal system - provides internal structure muscular system - provides mobility nervous system - coordinates voluntary and involuntary activity endocrine system - composed of hormone secreting glands cardiovascular system - circulates blood lymphatic system - part of the body's immune response respiratory system - provides oxygen for cellular respiration digestive system - provides nourishment and energy urinary system - serves to excrete wastes reproductive system - produces gametes for reproduction