How many organs are in the human body?

The number you've heard is 78. The honest answer is that nobody officially counts them — no anatomical body publishes a standing list — and depending on how you define "organ", the figure runs from 5 (the vital ones) to about 80 (with post-2017 additions) to around 91 on Wikipedia's full anatomical list. At microscopic scale it climbs well past 200.

Where the "78" actually comes from

Nowhere traceable. Lisa MJ Lee, associate professor of cell and developmental biology at the University of Colorado Denver, told Live Science in 2020 that "no one knows where the number originates" — it's the figure repeated by textbooks and school websites for decades, but no governing body publishes it. There's no international anatomical authority that maintains an official organ list. The International Federation of Associations of Anatomists (IFAA) standardises anatomical terminology, not counts. So "78" is essentially the most quoted answer to a question nobody officially adjudicates.

Wikipedia's own list of human organs notes the same thing in its opening lines and runs to roughly 91 entries — and even then warns the list isn't comprehensive.

What an organ even is

The working definition is: a collection of two or more tissue types organised into a structural unit that performs a specific function. That sentence is where the trouble starts. A gross anatomist looking at the body without a microscope counts fewer organs than a histologist looking at slides; each sweat gland and hair follicle is a tissue assembly that meets the definition, but listing them individually pushes the count past 200.

The five vital ones

One area where the count is uncontested: brain, heart, liver, kidneys, lungs. Lose any one of these completely and you don't survive without dialysis, transplant, or mechanical support. Notes worth knowing: humans can live normally on a single kidney; the liver can regenerate from as little as ~25% of its mass; and "one lung" is enough to live on, just at reduced capacity.

The two new ones (and why they matter)

In November 2016, J. Calvin Coffey and D. Peter O'Leary of the University of Limerick published a paper in The Lancet Gastroenterology & Hepatology arguing that the mesentery — the fold of peritoneum attaching the intestines to the abdominal wall — should be reclassified from "many fragments" to one continuous organ. The change was quickly accepted, nudging the conventional count from 78 to 79.

In March 2018, Petros Benias, Neil Theise and colleagues described the interstitium in Scientific Reports — a previously overlooked network of fluid-filled spaces running through connective tissue. Whether it qualifies as a single organ is still debated; if it does, the count nudges up again.

The 11 organ systems

The number of systems, unlike the number of organs, is reasonably settled at eleven in standard anatomy texts (some merge lymphatic into immune for ten; some split immune out for twelve).

Things you can lose and live

• Appendix — routinely removed in appendicectomy; no replacement needed.
• Gallbladder — removed in cholecystectomy; bile drips into the gut continuously instead of pooling.
• Spleen — splenectomy patients live normally with extra vaccination cover for certain bacteria.
• One kidney — the remaining kidney enlarges and takes over (compensatory hypertrophy).
• Stomach — total gastrectomy patients can live, with reconstructed plumbing and small frequent meals.
• Reproductive organs — life carries on, fertility doesn't.

Frequently asked

Sources

Related questions

Five if you mean "without which you die." Seventy-eight because everyone keeps saying so. Ninety-one if you actually try to list them. The body is the same body — the answer changes with the question.