THE DERMIS

 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.  The surface of the dermis is irregular because the dermis sends out kinds of projections multiple  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 is   the most superficial, it is  loose 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 which   is underneath is thicker  and 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.