organ
Meaning of organ: The level of organization between tissue and body system, where several kinds of tissue combine to do one job.
Definition of organ
An organ is a body structure built from several kinds of tissue working together on one main job. The heart pumps blood, the lungs exchange gases, the kidneys filter waste. Each organ has a characteristic shape, a blood supply and a nerve supply of its own, and each belongs to a larger system whose members share the work between them.
How is an organ put together?
Biology stacks its parts. Cells of one kind form a tissue, several tissues arranged together form an organ, and organs sharing a task form a system. The stomach shows the pattern. It has a lining that makes acid and mucus, a muscle coat that churns, connective tissue holding the layers together, nerves that time the contractions, and vessels supplying it all. Remove any one layer and the job fails. Shape follows function, which is why most organs are either hollow tubes or solid masses.
What are the main organ systems?
| System | Main organs | Job |
|---|---|---|
| Circulatory | Heart, blood vessels | Moves blood, oxygen and heat |
| Respiratory | Lungs, airways | Takes in oxygen, releases carbon dioxide |
| Digestive | Stomach, intestines, liver, pancreas | Breaks food down and absorbs it |
| Urinary | Kidneys, bladder | Filters blood and makes urine |
| Nervous | Brain, spinal cord, nerves | Senses, decides and controls |
Are all organs essential?
No. Some are vital, meaning life ends quickly without them or without a machine standing in, and the heart, brain, lungs and liver belong in that group. Others can be removed with adjustment, among them the gallbladder, the spleen and one of the two kidneys. The appendix can be removed with no lasting effect, although it appears to shelter gut bacteria. The skin is the largest organ of all and is easy to overlook because it lies spread out flat rather than packed into a lump.
What does organ failure mean?
Failure means an organ can no longer meet the body's demand, not that it has stopped altogether. In congestive heart failure the heart still beats but cannot move enough blood forward, so fluid backs up behind it. Kidney failure means filtering has fallen too low to keep the blood clean. Because the systems lean on one another, a single failing organ commonly drags others down, and several failing at once is the pattern that makes critical illness so dangerous.
Used in a sentence
The imaging report described the pelvic organs as normal in size and position.
Good to know
Organ failure describes an organ that can no longer meet demand rather than one that has stopped entirely, and because body systems depend on each other, failure in one organ commonly spreads to others.
Word origin
Where “organ” comes from
From the Greek organon, meaning tool or instrument, the same root behind organize.