Groups of Tissues Form Organs

Organs 

Organs are the next level of organization in the body. An organ is a structure made of two or more tissues that work together for a common purpose. Skin, the largest organ in the body, is shown in Figure below. Organs can be as primitive as the brain of a flatworm (a group of nerve cells), as large as the stem of a sequoia (up to 90 meters (300 feet) in height), or as complex as a human liver. The human body has many different organs including the heart, the kidneys, the pancreas, and the skin. Two or all of the tissue types can be found in each organ. Organs inside the body are called internal organs.