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The skin (integument) is a composite organ, made up of at least two major layers of tissue: the epidermis and the dermis. [2] The epidermis is the outermost layer, providing the initial barrier to the external environment. It is separated from the dermis by the basement membrane (basal lamina and reticular lamina).
This can be done in terms of the chemical elements present, or by molecular structure e.g., water, protein, fats (or lipids), hydroxyapatite (in bones), carbohydrates (such as glycogen and glucose) and DNA. In terms of tissue type, the body may be analyzed into water, fat, connective tissue, muscle, bone, etc.
This structure is commonly called "dermal armor" and serves to protect the organism, while also helping with temperature regulation. Osteoderms represent hard tissue components of the integument, making them easy to identify in fossil examination. [2] This dermal armor is found prominently in many lizards.
It is composed of 270 bones at the time of birth, [2] but later decreases to 206: 80 bones in the axial skeleton and 126 bones in the appendicular skeleton. 172 of 206 bones are part of a pair and the remaining 34 are unpaired. [3] Many small accessory bones, such as sesamoid bones, are not included in this.
For this reason it is thought that females may have evolved to have lighter skin in order to help their bodies absorb more calcium. [22] The Fitzpatrick scale [23] [24] is a numerical classification schema for human skin colour developed in 1975 as a way to classify the typical response of different types of skin to ultraviolet (UV) light:
To better understand the structure of avian skin, avian skin has been broken down into three different functional components: hydraulic skeleto-muscular apparatus of the feathers; This functional component consists of the only of the structural features of the feather tracts, namely the cutis, and connective tissue layer fascia superficialis ...
The word skin originally only referred to dressed and tanned animal hide and the usual word for human skin was hide. Skin is a borrowing from Old Norse skinn "animal hide, fur", ultimately from the Proto-Indo-European root *sek-, meaning "to cut" (probably a reference to the fact that in those times animal hide was commonly cut off to be used as garment).
A dermal bone or investing bone or membrane bone is a bony structure derived from intramembranous ossification forming components of the vertebrate skeleton, including much of the skull, jaws, gill covers, shoulder girdle, fin rays (lepidotrichia), and the shells of turtles and armadillos.