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WonderBody fact

Skin is the body's largest organ, covering 1.5 to 2 square metres (16 to 22 sq ft) in an average adult. On the forearm it is only about 1.3 millimetres thick, yet it keeps water in and germs out and helps control body temperature.

Human biology

Health

The story behind the card

Skin has three main layers. The outer layer, the epidermis, is a waterproof barrier made of flattened cells filled with a tough protein called keratin. New cells form at its base and move up to the surface, and the whole layer is replaced about every seven weeks. Beneath it, the dermis holds blood vessels, nerve endings, hair roots and sweat glands. The deepest layer, the hypodermis, stores fat that cushions and insulates the body. Skin senses touch, pressure, heat and pain, and it makes vitamin D when the sun's UVB rays reach it. Sweating, and the widening or narrowing of blood vessels near the surface, help keep body temperature steady.

Türkçe oku
Deri vücudun en büyük organıdır ve ortalama bir yetişkinde 1,5 ile 2 metrekare arasında bir alanı kaplar. Ön kolda kalınlığı yalnızca 1,3 milimetre kadardır; buna rağmen suyu içeride, mikropları dışarıda tutar ve vücut ısısının dengelenmesine yardım eder.

Derinin üç ana katmanı vardır. En dıştaki epidermis, keratin adlı dayanıklı bir proteinle dolu yassı hücrelerden oluşan su geçirmez bir engeldir. Yeni hücreler bu katmanın tabanında oluşup yüzeye doğru ilerler; katmanın tamamı yaklaşık yedi haftada bir yenilenir. Altındaki dermiste kan damarları, sinir uçları, kıl kökleri ve ter bezleri bulunur. En derindeki hipodermis ise yağ depolar; bu yağ vücudu darbelere karşı korur ve ısı kaybını azaltır. Deri dokunmayı, basıncı, sıcaklığı ve acıyı algılar; güneşin UVB ışınları değdiğinde de D vitamini üretir. Terleme ve yüzeye yakın damarların genişleyip daralması, vücut ısısının dengede kalmasını sağlar.

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