The skin is the largest organ of all vertebrates.
Its main functions are:
Protective (in terrestrial vertebrates it protects from drying out as well).
Sensitive or sensory: perception of pressure, temperature, vibration…
Excretory: elimination of waste substances.
In some vertebrates it also participates in thermoregulation and water balance through sweating and vasodilatation-vasoconstriction. For example, when it is hot, the vessels dilate so that heat is lost through the blood and vice versa.
![capas-piel-skin-layers-dermis-epidermis](https://sp-ao.shortpixel.ai/client/to_webp,q_glossy,ret_img,w_1024,h_832/https://periergeia.org/wp-content/uploads/2020/04/capas-piel-skin-layers-1024x832.png)
In all of vertebrates the skin always consists of 2 tunics:
Epidermis: this is the outermost layer, formed by a lining epithelium (layer of cells), which it is different according to the group of vertebrates.
Dermis: always formed by connective tissue (set of filling, supporting and connecting tissues).
In some body regions of mammals another deeper tunic may also appear > the hypodermis, formed by lax connective tissue (which also provides flexibility) and adipose tissue (fat).
![skin-structure-components](https://sp-ao.shortpixel.ai/client/to_webp,q_glossy,ret_img,w_1001,h_754/https://periergeia.org/wp-content/uploads/2020/04/skin-structure.jpg)
THE FACT
The skin of an adult human measures about 1.5-2m² and weighs about 4 kg.