The Dermis Lecture Notes

‭THE DERMIS‬ ‭✪It is the underlying layer of the epidermis. It is a connective tissue therefore of mesoblastic origin‬ ‭and it is a sort of intermediary between the epidermis and the hypodermis, that is to say the‬ ‭subcutaneous cellular tissue. The thickness varies from one place to another on the skin.‬ ‭ he surface of the dermis is irregular because the dermis sends out kinds of projections multiple‬ T ‭which are called the dermal papillae and these projections are nested in inverse projections of the‬ ‭epidermis, therefore the dermo-epidermal limit at the level of the basal layer, the basal lamina, this‬ ‭limit is extremely irregular with sorts of expansions which will become entangled with each other.‬ ‭These taste buds, these invaginations are even more numerous in areas of the skin which are‬ ‭subjected to pressure so this strengthens the skin's resistance.‬ ‭ At the surface of this dermis, there is the basal lamina which follows these interdigitations and‬ ✪ ‭this basal lamina is classic with the connective tissue (reticulin, glycosaminoglycan, fibrous‬ ‭proteins such as collagen, etc.) and it is at this level that the anchoring of the cells of the basal layer‬ ‭takes place via hemidesmosome which attach the basal cell to the fibrous proteins of the basal‬ ‭lamina. Here too we describe diseases of this dermo-epidermal junction: these are epidermolysis‬ ‭bullosa which results in a kind of skin detachment, bubbles and these epidermolysis bullosa are‬ ‭linked either to abnormalities of the hemidesmosomes or to abnormalities of collagen 7 in particular‬ ‭, acquired or constitutional anomaly. The dermis itself is made up of two layers: the papillary layer‬ ‭and the reticular layer.‬ ‭ ‬‭The papillary layer is‬‭the most superficial, it is‬‭loose connective tissue with ingredients usually:‬ ✪ ‭fibers, fibroblast cells and non-autochthonous cells such as macrophages, leukocytes,...‬ ‭At the level of the papillary layer and all layers of the dermis, elastic fibers which are fine and in‬ ‭this papillary layer they are perpendicular to the surface of the skin and go into tighten into the‬ ‭basal lamina. These particular fibers are the oxytalan fibers. So they will force a kind of axis to the‬ ‭papillae, to the outgrowths of this dermis and insert themselves at the level of the basal lamina‬ ‭therefore will stiffen this layer called papillary.‬ ‭ ‬‭The reticular layer which‬‭is underneath is thicker‬‭and it is more connective tissue dense‬ ✪ ‭with thick collagen fibers, therefore type 1, and then always the same ingredients but here there are‬ ‭more fibers and fewer cells and here again we find elastic fibers which are thick in the deepest areas‬ ‭of this reticular layer and that become thinner as we move closer to the epidermis, therefore finer‬ ‭towards the surface and thicker towards depth. Andit is this kind of network of elastic fibers which‬ ‭gives elasticity to the skin, which is responsible for this elasticity and this elastic network which‬ ‭deteriorate during aging and which will therefore end up disappearing or becoming rarer, which‬ ‭explains the formation of wrinkles.‬ ‭ These elastic fibers, at the level of the middle zone, fibers are called elaunin fibers so in this‬ ✪ ‭drawing we recognize the epidermis with irregularities, dermal papillae. In the most superficial‬ ‭zone of the dermis, there are these fibers which tend to be perpendicular to the surface and which‬ ‭will form the axes of the papillae, the axes of the oxylalan cells.‬ ‭ At the deepest layer, these elastic fibers are very dense and most of the time parallel to the surface‬ ✪ ‭and in the intermediate zone which is always part of the reticular dermis and in the most superficial‬ ‭part of the reticular dermis these elastic fibers have thinned and begin to curve to move from a‬ ‭parallel position the to the surface of the skin at a perpendicular position. At the level of this dermis,‬ ‭there is significant vascularization which will be described later. Here is the representation of the‬ ‭dermal papillae, therefore of these expansions which can take several aspects with both expansions‬ ‭of the epidermis in the dermis and vice versa and which gives rise to an irregular pattern of the‬ ‭epidermal-dermal junction.‬ ‭ Deteriorate during aging and which will therefore end up disappearing or becoming rarer, which‬ ✪ ‭explains the formation of wrinkles. These elastic fibers, at the level of the middle zone, fibers are‬ ‭called elaunin fibers so in this drawing we recognize the epidermis with irregularities, dermal‬ ‭papillae. In the most superficial zone of the dermis, there are these fibers which tend to be‬ ‭perpendicular to the surface and which will form the axes of the papillae, the axes of the oxylalan‬ ‭cells. At the deepest layer, these elastic fibers are very dense and most of the time parallel to the‬ ‭surface and in the intermediate zone which is always part of the reticular dermis and in the most‬ ‭superficial part of the reticular dermis these elastic fibers have thinned and begin to curve to move‬ ‭from a parallel position the to the surface of the skin at a perpendicular position.‬ ‭ At the level of this dermis, there is significant vascularization which will be described later. Here‬ ✪ ‭is the representation of the dermal papillae, therefore of these expansions which can take several‬ ‭aspects with both expansions of the epidermis in the dermis and vice versa and which gives rise to‬ ‭an irregular pattern of the epidermal-dermal junction.‬