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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 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.
Its purpose is to attach the skin to underlying bone and muscle as well as supplying it with blood vessels and nerves. It consists of loose connective tissue, adipose tissue and elastin. The main cell types are fibroblasts, macrophages and adipocytes (subcutaneous tissue contains 50% of body fat). Fat serves as padding and insulation for the body.
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).
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.
The subcutaneous tissue (from Latin subcutaneous ' beneath the skin '), also called the hypodermis, hypoderm (from Greek ' beneath the skin '), subcutis, or superficial fascia, [2] is the lowermost layer of the integumentary system in vertebrates. [3]
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.