Organdle: how the game works

Organdle is a daily anatomy puzzle drawn like a plate from an old atlas. You guess an organ, and each guess comes back as a row of clues: which body system it belongs to, where it lies, which germ layer it comes from, how many there are, where its blood comes from and how much it weighs. This page explains every column, the three levels and where the facts come from.

What it is

Every day at midnight, Zurich time, Organdle picks one organ for each of its three levels. Everyone gets the same organs. The list you guess from holds 112 organs and named organ parts, from the brain and the cerebellum to the nail and the sweat glands, and every one of them can be guessed on every level. You can type names in English, German, French, Italian or Latin: "liver", "Leber", "foie", "fegato" and "hepar" all find the same organ. Guesses are unlimited; what counts is how many you needed.

Whole organs and their parts are both on the list, because people type both: the brain and the cerebrum, the small intestine and the duodenum, the adrenal gland and its cortex, the skin and the dermis. Each has its own values, so a part can be close to its whole without being the same.

The three levels

• Classic: the answer is one of 89 organs that most people know or meet early in a course. Six columns.
• Hard: the answer can be any of the 105 organs that are allowed as answers, and the table gains two columns, peritoneum and epithelium.
• Rx: "Which organ do these medicines aim at?" The answer is one of 28 organs on which medicines from Pilldle's list act. You start with one clue; every wrong guess opens the next, up to five. Your guesses still get the six Classic columns.

Each level has its own answer, and no organ is the answer of two levels on the same day. Seven entries can be guessed but are never an answer: the six without a meaningful mass (nasal cavity, pericardium, pleura, greater omentum, mesentery, adenoid) and the large intestine, whose parts lie in different places relative to the peritoneum. The nasal cavity is the one exception: it can be an Rx answer.

The clues, column by column

Green means the same value, muted orange means close, an empty cell means no match. Green cells also carry a tick and orange cells a wavy sign, so the table reads without colour. A small triangle points up or down where a direction makes sense.

• System: one or two body systems. The pancreas is digestive and endocrine, the testis and ovary are reproductive and endocrine, the tongue is digestive and sensory, the diaphragm is musculoskeletal and respiratory. Green for the same set, orange for one in common.
• Region: where most of the organ lies, from top to bottom head, neck, thorax, abdomen, pelvis, or "whole body" for tissues found everywhere (skin, fat, lymph nodes, bone marrow, sweat glands, nails). Orange is the next region up or down; the triangle shows whether the answer lies nearer the head or the feet. Some placements are choices: the oesophagus, trachea and spinal cord count as thorax, the sigmoid colon as pelvis, the testis and epididymis as pelvis, the nearest region.
• Germ layer: ectoderm, neural crest, mesoderm or endoderm, for the main tissue and the lining. Hollow organs follow their lining, so the gut, the larynx and the pharynx are endoderm. Orange for a shared layer, and for neural crest against ectoderm, since the crest comes from the ectoderm.
• Count: single, pair, or several (three or more, or a tissue spread over many sites). Green or nothing.
• Arterial supply: the main arterial source, such as the coeliac trunk, the superior mesenteric artery, the internal carotid or the renal artery, from a fixed list of 20. Many organs also list secondary sources: the brain gets the internal carotid and the vertebral and basilar arteries, the lung the pulmonary arteries and the bronchial branches of the thoracic aorta. Green for the same main source; orange if the two organs share any source, or one main source branches from the other, or both hang on the same trunk (the aorta itself does not count). "Local arteries everywhere" and "No blood vessels" (cornea, lens, epidermis) only match themselves.
• Mass: adult grams; one organ for a pair, all together for "several". Green within 15 percent of the answer, orange within a factor of 2, compared on a log scale; the triangle says heavier or lighter. A "~" marks an estimate, and an estimate never turns green.
• Peritoneum (Hard): intraperitoneal, retroperitoneal (primary or secondary), subperitoneal, or not abdominal. Orange for the two retroperitoneal kinds, and for intraperitoneal against secondary retroperitoneal.
• Epithelium (Hard): the characteristic lining or tissue. Orange within a family: stratified (both squamous kinds and urothelium) or simple (columnar, cuboidal, squamous, pseudostratified ciliated).

The Rx clues

Rx uses a frozen copy of Pilldle's medicine data. Only groups of the ATC classification that clearly point at one organ count, so antibiotics, painkillers, insulin and other medicines that act all over the body are left out. The five clues come in a fixed order: a class of medicines that acts there, a named medicine, a side effect felt there (or another medicine when Pilldle has none), the body system, and the region. For the small intestine, for example, the clues start with cholesterol absorption inhibitors, then acarbose, then oily stools. When some members of a class act elsewhere, the clue says how many.

Hints

Classic offers the first letter of the organ's name after 4 guesses and its Latin name after 7. Hard offers the same after 5 and 8. Rx offers the Latin name after 6. A Latin name such as "ren", "lien" or "hepar" can give the answer away to anyone who has met it in medical words, which is why it comes late.

How to play well

• Open with an organ that splits the body: the liver or the stomach tells you at once whether the answer is above or below the diaphragm, and the region triangle narrows it further.
• Use the mass column. Organs span from a fraction of a gram (pineal gland) to kilograms (skin, fat). Two or three guesses with the triangle find the right weight class quickly.
• Orange on arterial supply is a map: the coeliac trunk feeds the stomach, liver, spleen and the upper duodenum; the superior mesenteric artery the small intestine and the right colon; the inferior mesenteric artery the left colon and rectum.
• Germ layer separates the gut and its glands (endoderm) from the nervous system and skin (ectoderm) and from the heart, kidneys and gonads (mesoderm).
• In Rx, think of where a medicine works, not what it treats: beta blockers point at the heart, statins at the liver, triptans at the trigeminal ganglion.

Data and sources

Every value was curated by hand from standard anatomy and embryology teaching and checked against Terminologia Anatomica (TA98), Wikidata and ICRP Publication 89. Wikidata (CC0) supplies identifiers, TA98 codes and Latin terms. Masses are ICRP 89 reference values for an adult man (an adult woman for the ovary, uterus and breast) where they exist: 39 organs. Thirteen are other published values, 54 are our own estimates (mostly small parts of the brain, eye and ear), and six have no single meaningful mass. Wikipedia page views helped sort the organs into the Classic and Hard pools.

Where textbooks disagree, a value was chosen and the choice is written down. The thyroid's main artery is the external carotid, though the inferior thyroid artery is about as large. The urinary bladder counts as endoderm, with the trigone noted as mesoderm. The lung's mass includes its blood, the heart's does not. The answer panel shows these notes. External genitalia are not in the game. Organdle is for learning and fun, not medical advice.

Questions

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