Corpus: Organ

In biology, the term organ refers to a part of the body composed of various tissues that represents a distinct functional unit. An organ can exist both as a distinct body element (e.g. liver) and in the form of a cell system distributed throughout the body (e.g. blood).

An organ usually consists of a specialized functional tissue, the parenchyma and the connective supporting tissue (stroma).

In their entirety, the organs form the organism. The equivalent of the organ at the cellular level is the organelle. Organ-like microstructures that are cultivated from stem cells are called organoids.

The organs are formed during the embryonic period through a process called organogenesis. In anatomy, organs are studied individually but are also grouped into functional units known as organ systems. Examples include the respiratory system, excretory system, and reproductive system. This classification applies not only to human organ systems but also to those of animals and plants. Unicellular organisms typically possess only one organ-like structure.

Human medicine has sometimes been criticized for focusing too narrowly on individual parts of the body, leading to a loss of understanding of the whole person. Despite significant advancements, this approach is often referred to as "organ-centered medicine."

4.1. ...according to location

A rough distinction is made between

• the visible external organs (primarily the skin) and
• the non-visible internal organs (e.g. the heart) located inside the body

4.2. ...according to function

• respiratory organs
• circulatory organs
• excretory organs
• sexual organs
• sensory organs
• digestive organs
• movement organs