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Among the several adaptations that favor the conquest of the terrestrial environment by the vertebrates stand out an efficient waterproofed body coating, an adequate skeletal support system of the organism and its organs and a skillful mechanism that allows the movement of the organism through the environment.
In man these three tasks are performed, in order, by the skin, by the set of bones of the skeletal system and the numerous muscles components of the muscular system. Bones and muscles constitute the locomotor system.
Body lining: integument
The animals have a body covering whose main function is to protect the body against the entry of foreign bodies: the integument (from Latin tegumentum, cover, wrap). In addition to the protective function, the integument may also, depending on the species of animal, perform gas exchange, secrete substances, perceive stimuli and regulate body temperature, among other functions.
The invertebrate integument is usually a simple epithelium, consisting of a single layer of cubic or columnar cells. Already the vertebrate integument, the skin, is formed by two layers of tissues, with glands and attached structures.
The skin of vertebrates is formed by two distinct tissues, firmly joined together. The most external epithelial tissue is the epidermis. The most internal, connective, is the dermis.
The epidermis is an epithelium multistratified, that is, formed by several layers (strata) of juxtaposed cells. The innermost epidermal layer is called the germ layer, and is formed by cells that continually multiply, so that the newly generated cells push the older cells upward toward the surface of the body. As they age, the epidermal cells become flattened and manufacture and accumulate a resistant protein within themselves. keratin.
The most superficial cells, when they become full of keratin, die and constitute a friction-resistant and highly impervious to water loss coating.
The dermis, located immediately under the epidermis, is a connective tissue that contains protein fibers, blood vessels, nerve endings, sensory organs, and glands. The main cells of the dermis are the fibroblasts, responsible for the production of fiber and a gelatinous substance, the amorphous substance, in which the dermal elements are immersed. It is the dermis fibers that give the skin resistance and elasticity.
The dermis blood vessels are responsible for the nutrition and oxygenation of both dermal and epidermal cells. In mammals dermis blood vessels play an important role in maintenance of body temperature. When body temperature rises, nerve impulses cause the blood vessels in the dermis to dilate; This causes more blood to circulate in the skin, leading to increased heat radiation to the environment, which causes the body to cool. When body temperature decreases, the blood vessels in the skin contract; As a result, less blood begins to circulate on the body surface, which reduces heat loss.
Nerve endings and sensory organs present in the dermis are responsible for perceptions of heat, cold, viscosity, hardness, humidity, roughness, softness, etc.
Subcutaneous tissue (hypodermis)
Under the skin is a layer of loose connective tissue - the subcutaneous tissue - rich in fiber and cells that store fat (fat cells). Fat stored in subcutaneous tissue is a reserve of energy and acts as a thermal insulator.