--- title: "The human body — organs, bones, blood and senses" description: "How many bones, how much blood, how many senses. Organs, teeth and body figures, plus the widely repeated claims that turn out to be wrong." url: https://atoneplace.net/body/ site: "At One Place" --- # The human body 15 entries on organs, bones, teeth, blood, senses and the body in numbers. Structural reference rather than health advice — what a thing is, where it is, and what it does. ## Things everyone knows that are wrong - The heart is not on the left. It sits near the centre, angled so the apex points left, which is why the beat is felt there. - You do not use only ten per cent of your brain. Imaging shows essentially all of it active over a day, and there is no dormant reserve — damage to almost any region produces deficits. - Lungs do not "pull" air in. Air is pushed in by atmospheric pressure once the diaphragm lowers and the chest volume increases — which is why a punctured chest cavity stops the lung inflating even though the lung is undamaged. - The count of 206 is a convention, not a constant. A minority of people have extra sesamoid bones or an additional rib, and the figure depends on whether such variants are counted. - The blood type diet has no evidence behind it. A controlled study found the diets produced effects unrelated to the participants’ actual blood groups. - Deoxygenated blood is not blue. It is dark red. Veins look blue because of how skin scatters light, not because of the blood inside them. - The five-senses framing comes from Aristotle and does not reflect the anatomy. Touch alone covers at least four separate receptor systems for pressure, vibration, temperature and pain. - The tongue map is wrong. The idea that sweet is tasted at the tip and bitter at the back comes from a mistranslation of a 1901 German paper and was disproved in 1974. Every basic taste is detectable across the whole tongue. - The claim that bacteria outnumber human cells ten to one is obsolete. It traced to a 1972 estimate never intended as precise; careful counting puts the ratio close to 1:1. ## Organs - [Heart](https://atoneplace.net/body/heart/) — A four-chambered pump, roughly fist-sized, beating about 100,000 times a day. - [Brain](https://atoneplace.net/body/brain/) — About 1.4 kg, using roughly 20% of the body’s energy at 2% of its mass. - [Liver](https://atoneplace.net/body/liver/) — The largest internal organ, around 1.5 kg, and the only one that regenerates. - [Lungs](https://atoneplace.net/body/lungs/) — Two unequal lungs with a gas-exchange surface of about 70 square metres. - [Skin](https://atoneplace.net/body/skin/) — The largest organ — about 2 m² and 4 kg in an adult. - [Kidneys](https://atoneplace.net/body/kidneys/) — Two fist-sized filters processing about 180 litres of blood a day. ## Bones - [Bones](https://atoneplace.net/body/bones/) — 206 in the adult skeleton, down from about 270 at birth. - [Femur](https://atoneplace.net/body/femur/) — The longest and strongest bone — about a quarter of adult height. ## Teeth - [Teeth](https://atoneplace.net/body/teeth/) — 32 adult teeth including wisdom teeth; 20 in the primary set. ## Blood - [Blood types](https://atoneplace.net/body/blood-types/) — Eight common groups from the ABO and Rh systems — O+ is the most frequent. - [Blood](https://atoneplace.net/body/blood/) — About 5 litres in an adult, roughly 7% of body weight. ## Senses - [The senses](https://atoneplace.net/body/senses/) — Far more than five — at least nine, and by some counts over twenty. - [Taste](https://atoneplace.net/body/taste/) — Five basic tastes, detected across the whole tongue rather than in zones. ## Body in numbers - [Body water](https://atoneplace.net/body/body-water/) — About 60% of an adult male by mass, 55% of an adult female. - [Cells in the body](https://atoneplace.net/body/cells/) — About 36 trillion, of which roughly 80% are red blood cells. > None of this is medical advice. Individual variation in every figure is substantial, and anything about your own health belongs with a clinician. ## Common questions ### How many bones are in the human body? 206 in the adult, down from about 270 at birth as the skull, sacrum and coccyx fuse. More than half are in the hands and feet. ### How many senses do humans have? More than five. Proprioception, balance, temperature, pain and several interoceptive senses all have distinct receptors and pathways — nine or more by common counts. ### Do we only use 10% of our brain? No. Imaging shows essentially all of it active over a day, and damage to almost any region produces deficits. There is no dormant reserve. ### Is the tongue map real? No. It came from a mistranslation of a 1901 paper and was disproved in 1974. All five basic tastes are detectable across the whole tongue.