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A 2016 estimate found that a typical adult man weighing 70 kg has about 30 trillion human cells and 38 trillion bacteria. That overturned the old claim that bacteria outnumber our own cells ten to one: the two numbers are roughly equal.

PLOS Biology, 2016

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The estimate comes from Ron Sender, Shai Fuchs and Ron Milo of the Weizmann Institute of Science in Israel. Their reference man is 20 to 30 years old, 170 cm tall and weighs 70 kg. The ten-to-one figure, they found, went back to a single rough calculation from 1972 that had been repeated for decades. Almost all the bacteria live in the colon, the last part of the gut, and together they weigh only about 0.2 kg. Among human cells, red blood cells dominate the count, making up about 84 per cent, while fat and muscle cells, far fewer but much larger, make up most of the body's cell mass. The balance also shifts through the day: a single trip to the toilet empties a quarter to a third of the colon's contents.

Türkçe oku
2016'da yapılan bir hesaplamaya göre 70 kilogramlık ortalama bir yetişkin erkeğin vücudunda yaklaşık 30 trilyon insan hücresi ve 38 trilyon bakteri bulunur. Bu sonuç, bakterilerin kendi hücrelerimizden on kat fazla olduğu yönündeki eski iddiayı çürüttü: İki sayı aşağı yukarı birbirine eşit.
PLOS Biology, 2016

Hesaplama, İsrail'deki Weizmann Bilim Enstitüsü'nden Ron Sender, Shai Fuchs ve Ron Milo'ya ait. Esas aldıkları “referans insan”, 20 ile 30 yaş arasında, 170 cm boyunda ve 70 kg ağırlığında bir erkektir. Araştırmacılar, on kat iddiasının 1972'de yapılmış kaba bir tahmine dayandığını ve onlarca yıl boyunca sorgulanmadan tekrarlandığını gösterdi. Bakterilerin neredeyse tamamı bağırsağın son bölümü olan kalın bağırsakta yaşar ve hepsinin toplam ağırlığı yalnızca 0,2 kg kadardır. İnsan hücrelerinin sayıca yaklaşık yüzde 84'ü alyuvardır, yani kırmızı kan hücresidir; sayıca çok daha az ama çok daha iri olan yağ ve kas hücreleri ise vücuttaki hücre kütlesinin büyük kısmını oluşturur. Denge gün içinde de değişir: Tuvalete her gidiş, kalın bağırsaktaki içeriğin dörtte biri ile üçte biri arasında bir kısmını boşaltır.

Sources and further reading

Background reading: Human microbiome
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