Is it true that the skin is the largest human organ by area?

It is widely believed that the largest organ of the human body by area is the skin. We checked whether this is actually true.

This statement is found not only in blogs and on news portals, but also in "Wikipedia", in magazines National Geographic And "Around the world", V scientific articles, websites TV channels, manufacturers cosmetics, government medical institutions and private clinics.

Skin is the outer cover human and animal bodies. It protects against mechanical, chemical, biological and UV influences, provides touch and sensitivity, and is involved in thermoregulation, respiration, excretory and immune functions. Skin is considered an organ rather than just a tissue because it is made up of several different types of tissue that work together to perform complex and important functions. The skin has the epidermis (outer layer), dermis (layer below the epidermis), and subcutaneous fatty tissue. In addition, the skin contains various components such as blood vessels, nerve endings, sweat and sebaceous glands.

The area of ​​a person's skin depends on his height and weight, but on average it amounts to 2 sq. m. More accurately, the individual skin area can be calculated using this formula: weight in kilograms to the power of 0.425 and height in centimeters to the power of 0.725 multiplied by each other and further multiplied by 0.007184.

However, these calculations will only be correct if we consider the skin to be simply a flat surface. To this inaccuracy in 2018 paid attention dermatologist Richard Gallo from the University of California, San Diego. If we take into account hair follicles, sweat and sebaceous glands, the actual skin area will be almost 25 square meters. m.

But even if we take this refined measurement into account, the skin will still not be a record holder in area. In 2014, Swedish scientists, armed with light and electron microscopes as the most accurate measuring instruments, studied intestinal biopsy samples taken from healthy volunteers. The average length of the intestine is 5 m, two thirds of which is the small intestine. The internal diameter of the small intestine is approximately 2.5 cm, and the large intestine is 4.8 cm. Intestinal villi located in the small intestine increase its area by 60–120 times, and the same villi of the large intestine increase its area by 6.5 times. On average, it turns out that the area of ​​the adult human intestine is 32 square meters. m.

And even this is not the limit. In 1967, American explorer William Thurlbeck compared area of ​​the lungs of people who died or were emphysema, or from other reasons not related to respiratory pathologies. Depending on the cause of death, the area of ​​the lungs ranged from 40 to 100 square meters. m. In 1972, in a similar study, British specialist Philip Haslton appreciated Lung area ranges from 23.56 to 68.76 square meters. m. According to his data, the area of ​​the lungs on average was about 50 square meters. m. Finally, by calculations Swiss anatomist Ewald Weibel, the lung area ranges from 80 to 180 square meters. m. Thus, the lungs are most likely the largest organ of the human body by area.

Talking about different area estimates and the calculations that led to them, American experts notethat initially scientists tried to measure the area of ​​human organs within the framework of Euclidean geometry. “Euclidean shapes, such as the perfect square or sphere, almost never occur naturally. While fractals are present everywhere in nature: from the branching of trees to river networks, from the pattern of stars in the galaxy to vortexes,” they write. If you consider a tree - a striking example of a fractal - it will become clear: inscribed in a three-dimensional cube, it occupies a smaller volume than the cube itself, but larger than a two-dimensional rectangle. Therefore, to estimate both volume and area, one should resort to fractal rather than Euclidean dimensions. 

At the same time, no one has yet tried to estimate the fractal dimension of organs, taking into account all their irregularities down to the molecular level. Therefore, as a first approximation, that is, taking into account the visible surface area, the skin is definitely not in first place. Calculations show that the area of ​​the intestines exceeds the area of ​​the skin, and the largest human organ by area is the lungs.

Cover image: Image by Pana Koutloumpasis from Pixabay

Not true

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