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The dermis
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Made up of 80% water, elastin fibres and collagen floating in a glycoprotein gel, the dermis is the tissue supporting the skin. In contrast with the epidermis, it is vascularised, enabling it to not only provide energy and nutrition to the epidermis but also to play a primordial role in thermoregulation and in healing.
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Dermal papilla in scanning electron microscopy
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Collagen and elastin fibers in Scanning electron microscopy
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The dermis is 10 to 40 times thicker than the epidermis. At the junction with the epidermis, its surface bristles with fibrous, vascular and nervous projections - the dermal papillae.
The fibroblasts are the main cells in the dermis. They are essentially located in the dermal papillae close to the epidermis, and found only in very low numbers in the deep layers of the dermis known as the reticular dermis. They are specialised in producing two types of protein fibres, collagen and elastin fibres constituent of the extra-cellular matrix. Collagen fibres, 70% of the proteins in the dermis, gives dermis its resistance to strain and traction, while elastin supply its elastic properties.
The reticular dermis accounts for the greater part of the dermis. On this level, the elastin and collagen fibres are multidirectional, whereas in the dermal papillae the elastin fibres are mainly oriented perpendicular to the skin surface.
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Scanning electron microscopy of Blood capillary. Red blood cell inside the capillary.
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A large number of blood vessels, small in diameter organised into plexus
, cover the entire upper level of the dermis, but do not penetrate the epidermis. In particular, they are concentrated beneath the dermal papillae and even deeper, almost in contact with the hypodermis. They bring nutrients to the epidermis and contribute to cutaneous thermoregulation.
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Nerves include free nerve endings, that penetrate the epidermis a little or are linked to nervous corpuscles including the Meissner, Pacini and Ruffini corpuscles, which generate sensations coming from the skin - touch, temperature, or pressure.
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A specific kind of structure 75 nm thick is to be found at the junction between the dermis and the epidermis. This is called the dermo-epidermal junction. This structure enables the keratinocytes in the epidermis to be rooted in the dermal papillae, while on the side of the dermis, the anchoring fibres interact with the basal membrane to create a network which traps the collagen fibres of the upper part of the dermis.
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