Skin Is Not the Largest Organ
2013; Elsevier BV; Volume: 134; Issue: 2 Linguagem: Inglês
10.1038/jid.2013.335
ISSN1523-1747
Autores Tópico(s)Dermatologic Treatments and Research
ResumoTO THE EDITOR When scanning the newly published literature cited on PubMed/Medline, it is almost a weekly occurrence that I see something go by stating that the skin is the largest organ in the human body. The problem is that there is no factual basis for this ubiquitous dogmatic statement. As an example, the editor's introduction to the timely and informative Review Series on Dermatology that appeared in the 1 February 2012 issue (volume 122, issue 2) of the Journal of Clinical Investigation began with the following sentence "Though the body's largest organ, the skin may be occasionally forgotten as a site of clinically important disease." Similar statements have been made in earlier Journal of Investigative Dermatology publications authored by prominent dermatology/skin biology investigators (Setoguchi et al., 1994Setoguchi Y. Jaffe H.A. Danel C. et al.Ex vivo and in vivo gene transfer to the skin using replication-deficient recombinant adenovirus vectors.J Invest Dermatol. 1994; 102: 415-421Abstract Full Text PDF PubMed Scopus (98) Google Scholar; Bickers and Athar, 2006Bickers D.R. Athar M. Oxidative stress in the pathogenesis of skin disease.J Invest Dermatol. 2006; 126: 2565-2575Abstract Full Text Full Text PDF PubMed Scopus (820) Google Scholar; Clark et al., 2007Clark R.A. Ghosh K. Tonnesen M.G. Tissue engineering for cutaneous wounds.J Invest Dermatol. 2007; 127: 1018-1029Abstract Full Text Full Text PDF PubMed Scopus (385) Google Scholar). On 31 May 2013, a PubMed search using the phrase, "skin largest organ" returned 194 citations. A review of the text of the abstracts accompanying the first 20 of those citations revealed that in 16 (80%) it was specifically stated that the skin is the largest human organ. However, published data simply do not support the "common knowledge" proposition that the skin is the largest organ in the human body. An earlier analysis of this question by Goldsmith, 1990Goldsmith L.A. My organ is bigger than your organ.Arch Dermatol. 1990; 126: 301-302Crossref PubMed Scopus (37) Google Scholar) eloquently and humorously concluded that the human skin is not the largest organ in the human body. By weight, the skin may be considered to be the largest of the "medium-sized" organs such as the liver and brain. However, the skin is no match in weight for the much larger organs of the musculoskeletal system. In such comparisons, clearly the musculoskeletal system must be considered as a human organ system. Goldsmith, 1990Goldsmith L.A. My organ is bigger than your organ.Arch Dermatol. 1990; 126: 301-302Crossref PubMed Scopus (37) Google Scholar) assumptions and calculations resulted in a determination that the human skin (epidermis plus dermis) weighs 3.86 kg, or 5.5% of the total body weight of the proverbial 70 kg man. It has been reported that the skeleton accounts for ∼14% of the human body's weight (Reynolds, 1977Reynolds W.J. Skeleton weight allometry in acquatic and terrestrial vertebrates.Hydrobiologia. 1977; 56: 35-37Crossref Scopus (16) Google Scholar). In addition, it has been reported that an average adult male is made up of 42% of skeletal muscle and an average adult female is made up of 36% (as a percentage of body mass; Marieb and Hoehn, 2007Marieb E.N. Hoehn K. 7th ed. Human Anatomy & Physiology. Pearson Benjamin Cummings, San Francisco2007: 317Google Scholar). If one included the subcutaneous fat, the skin by mass would be a stronger contender for being the largest organ in the human body. However, as its name implies "subcutaneous" fat is not an official part of the skin. Wikipedia also states that human skin is the largest organ. However, Wikipedia, that fount of conventional wisdom, also states that the skin is composed of the epidermis and dermis. It specifies that the hypodermis (subcutaneous tissue) underlies the skin but is not part of the skin (http://en.wikipedia.org/wiki/Skin#Hypodermis/, accessed 31 May 2013). Nor can the skin be considered to be the largest human organ with respect to functional surface area. The human skin surface area is identical to body surface area. The body surface area of the proverbial 70 kg man is 1.7 m2 (Goldsmith, 1990Goldsmith L.A. My organ is bigger than your organ.Arch Dermatol. 1990; 126: 301-302Crossref PubMed Scopus (37) Google Scholar). By comparison, the gas exchanging surface of the lung's airways has been estimated to be 70 m2 (Notter, 2000Notter R.H. Lung Surfactants: Basic Science and Clinical Applications. Marcel Dekker, New York2000: 120Google Scholar), which is approximately half the size of a tennis court. The mucosal surface of the human gastrointestinal tract has been estimated to be the size of a football field. Thus, with apologies to all those dermatologists who for so long have felt emboldened by the thought that theirs is the largest organ, in neither weight nor functional surface area can the human skin be considered to be human body's largest organ.
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