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How many organs are in the human body?

Since ancient times, humankind has sought to understand the guts inside us. Ancient Egyptians handled human organs as they removed them for embalming. Medical manuscripts found in an ancient Chinese tomb may be the earliest-known anatomical writing about the human body. Thousands of years later, do we know how many organs are in the human body?

Organs are collections of tissues that work together for a common goal, explained Lisa M.J. Lee, an associate professor in the Department of Cell & Developmental Biology at the University of Colorado School of Medicine. “Every organ provides a function for human performance or survival,” she told Live Science.

But not every organ is necessary for survival. Only five organs — the brain, heart, liver, at least one kidney, and at least one lung are absolutely essential for living. Losing total function of any one of these vital organs spells death. Remarkably, the human body can survive without a lot of other organs, or by replacing a non-functioning organ with a medical device. 

Related: Why do we have an appendix?

As for counting organs in the human body, it depends on whom you ask and how you count, Lee said. Although no one knows where the number originates, the general count is 78 organs, she said. This list includes the vital organs: the tongue, stomach, thyroid, urethra, pancreas, plus many other single or pairs of organs. Bones and teeth are each counted only once.

Among anatomists, viewpoints differ on what counts as an organ. A histologist like Lee, who studies tissue at the microscopic level, may have a longer list of organs than a gross anatomist, who studies what’s visible to the unaided eye. For example, scientists made headlines in 2017 for labeling the mesentery, which attaches the intestines to the abdominal wall, as an organ. Even though the scientists provided new evidence to call it an organ, it was not controversial, as many histologists and anatomists agreed, Lee explained. But there’s no group charged with keeping an official count of the organs or deciding what qualifies as an organ. 

Thinking microscopically, when multiple types of tissues join together and function together, the unit is an organ, she said. Lee could call a nail, or structures that support the nail, an organ, and count each tooth as an individual organ. “I would consider each bone an organ, and all 206 bones collectively together, is considered an organ system.” Because bones are already listed once on the list of 78, to get a tally of the total number of organs using this definition, just add 205, for a total of 284 organs.

Counting each tooth separately brings the list to 315 organs. Many other organs are listed only once, even though there are many of them throughout the body. For instance, ligaments and tendons could dramatically increase the total number of organs when counted individually. This game is endless. The list of 78 counts the nerves just once, but

Dogs’ brains aren’t hardwired to care about human faces, study shows

Researchers measured brain activity in dogs and humans as they showed them videos of faces and backs of heads, a press release from Eötvös Loránd University, in Hungary, said.

While faces are hugely important for visual communication in humans, the same can’t be said for our canine companions.

Experiments involving functional magnetic resonance imaging on 20 dogs were carried out at Eötvös Loránd University and the National Autonomous University of México, Querétaro, Mexico, two of very few facilities that can scan dogs’ brains when they are awake and unrestrained.

Results revealed large dedicated neural networks in human brains are used to differentiate faces from non-faces. In dogs there are no brain regions that fire to differentiate faces.

Instead, dogs use more information from smell or larger parts of the body, study co-author Attila Andics of Eötvös Loránd University, told CNN.

Germans could legally have to let their dogs out twice a day

“In dogs, for kin recognition and mate selection facial cues are not more important than non-facial bodily cues, acoustic or chemical signals,” Andics said.

The full study, described by researchers as the first one of its kind, was published in the Journal of Neuroscience Monday.

Andics told CNN that dogs do care about human faces, even if their brains aren’t specifically tuned into them.

“I think it is amazing that, despite apparently not having a specialized neural machinery to process faces, dogs nevertheless excel at eye contact, following gaze, reading emotions from our face, and they can even recognize their owner by the face,” Andics said.

“During domestication, dogs adapted to the human social environment, and living with humans they quickly learn that reading facial cues makes sense, just as humans learn to pay attention to little details, of let’s say, a phone, without having specialized phone areas in their brain.”

Researchers will now compare how dog and human brains process other visual categories such as body parts, various species and everyday objects, said Andics.

The team will also investigate whether dog brains have developed different specializations as a result of living with humans, Andics added.

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