Organs

An organ is a distinct structure composed of multiple tissue types that together carry out one or more specific physiological functions essential to an organism’s survival. In multicellular animals and plants, organs are organized into higher-level collections called organ systems, which coordinate the body’s activities in response to internal and external cues.

In animals, common examples include the heart (pumps blood), the lungs (exchange of gases), the liver (metabolizes nutrients and detoxifies), the kidneys (filters blood and forms urine), the brain (coordinates behavior and body processes), and the digestive organs such as the stomach and intestines (break down food and absorb nutrients). The skin also functions as an organ, providing protection and regulatory roles. In plants, organs such as leaves, stems, and roots perform photosynthesis, transport water and nutrients, store resources, and provide structural support.

Organs typically consist of two or more tissue types, including epithelial, connective, muscle, and nervous tissues, and are supported by blood supply and innervation. They develop during embryogenesis from germ layers and undergo ongoing maintenance, repair, and sometimes regeneration.

Functions of organs are integrated across organ systems to maintain homeostasis, respond to stress, and support growth and reproduction. Pathology can arise from organ failure, injury, or disease, and some organs can be transplanted or replaced with medical interventions.

Note: the word organ can also refer to a musical keyboard instrument, a usage unrelated to the biological sense described here.