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StatPearls . Treasure Island (FL): StatPearls Publishing; 2021 Jan-.


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Introduction

The dermis is a connective tissue layer sandwiched between the epidermis and subcutaneous tissue. The dermis is a fibrous structure composed that collagen, elastic tissue, and also other extracellular materials that includes vasculature, nerve endings, hair follicles, and also glands. The function of the dermis is come support and protect the skin and also deeper layers, help in thermoregulation, and aid in sensation. Fibroblasts are the major cells within the dermis, but histiocytes, mast cells, and also adipocytes also play important roles in maintaining the normal structure and function of the dermis.  


Structure

The dermis is a connective organization layer that mesenchymal origin located deep come the epidermis and superficial come the subcutaneous fat layer.<1> The composition of the dermis is largely fibrous, consists of both collagen and also elastic fibers. In between the fibrous materials lies one amorphous extracellular "ground substance" include glycosaminoglycans, such together hyaluronic acid, proteoglycans, and also glycoproteins. 

The dermis is separated into two layers: the papillary dermis and the reticular dermis. The papillary dermis is the superficial layer, lie deep to the epidermis. The papillary dermis is created of loose connective tissue that is very vascular. The reticular great is the deep layer, forming a special layer of thick connective tissue that constitutes the bulk that the dermis. 

Collagen is the principal component that the dermis. Specifically, kind I and type III collagen are discovered in abundance. Elastic fibers also play an important structural role within the dermis. Elastic fibers room composed that elastin and also fibrillin microfibrils. In comparison to collagen, the biochemical configuration the elastin permits for gliding, stretching, and recoiling of fibers.<2> The reticular dermis comprises thick elastic fibers. Two subtypes the elastic fibers space worth more discussion: elaunin and oxytalan fibers<3>. Elaunin fibers space horizontally i ordered it elastic fibers discovered near the junction the the papillary and also reticular dermis. Oxytalan fibers space perpendicular elastic fibers found in the papillary dermis.<4>

The dermis houses blood vessels, nerve endings, hair follicles, and glands. There are countless cell species found within the connective organization of the dermis, consisting of fibroblasts, macrophages, adipocytes, mast cells, Schwann cells, and also stem cells.<5> Fibroblasts room the primary cell that the dermis. Mast cells are frequently found surrounding dermal capillaries.


Function

Skin Support and also Protection

The structure of the dermis gives a connective tissue framework for strength, flexibility, and also protection the the depths anatomical structures. Collagen and also extracellular contents like hyaluronic mountain fortify the skin and facilitate an anchor because that the epidermis via hemidesmosomes and other adhesive basement membrane zone (BMZ) components.<6> Oxytalan fibers may additionally play a duty in anchoring the epidermis. Elastic tissue also helps support the skin and carry out flexibility. The blood ship in the dermis are an essential for maintain of the epidermis and epidermal appendages. Nutrient via blood assistance the epidermis, hair follicles, and sweat glands. The vascular network further permits the dermis to organize an inflammatory an answer via recruitment the neutrophils, lymphocytes, and other inflammation cells. The dermal blood supply additionally plays a duty in temperature regulation debated below. 

Thermoregulation

Vasoactive dermal vessels regulate body temperature. Committed structures referred to as glomus bodies also take component in thermoregulation with AV shunt formation.<7> Glomus bodies room complexes the glomus cells, vessels, and smooth muscle cell that predominate in the digits, palms, and soles.<8> Although frequently within the dermis, eccrine sweat glands are ectoderm-derived epidermal appendages the invaginate right into the deeper organization of the dermis and subcutaneous layer.<9> 

Sensation

Several mechanoreceptors are current in the dermis. Nerve endings in the dermis surround hair follicles. These nerve endings sense hair movement and also act as mechanoreceptors allowing sensation come extend past the skin"s surface. Deep press receptors also exist. Pacinian corpuscles space large, lamellar, ovoid structures uncovered in the deep dermis and also they provide deep pressure and also vibratory sensation. Meissner"s corpuscles, located in the dermal papillae that the papillary dermis, respond come low-frequency stimuli. Meissner"s corpuscles are focused in glabrous (hairless) skin.<10> 

Cells that the Dermis and Their Function

The dermis contains many cabinet types. Fibroblasts, the principal cell that the dermis, manage the synthetic of collagen, elastic and also reticular fibers, and extracellular matrix material. Histiocytes room tissue macrophages existing within the connective organization that aid the immune system. Mast cells space inflammatory cell located in the perivascular areas of the dermis. Mast cells secrete vasoactive and also proinflammatory mediators essential in inflammation reactions, collagen remodeling, and also wound healing.<11> Dermal adipocytes are a distinct cell population from the subcutaneous adipose tissue. Dermal adipocytes not only carry out insulation and also energy storage but also assist in hair follicle regeneration and also wound healing.<12><13>


Tissue Preparation

The dermis is examined using a typical skin biopsy. The organization sample should very first be fixated with formalin come preserve tissue structure. After fixation, the specimen is dehydrated through an alcohol (e.g., ethanol) to remove water. The alcohol certified dealer is then cleared utilizing xylol. After, the tissue sample is embedded in paraffin. After hardening the the paraffin medium, a microtome slices the specimen. The tissue specimen may be stained according to hematoxylin and also eosin (H&E) staining protocols. 


Histochemistry and also Cytochemistry

Immunofluorescence of organization samples is an important diagnostic tool in autoimmune blistering diseases such together bullous pemphigoid and dermatitis herpetiformis. For example, straight deposition that immunoglobulin G (IgG) and complement (C3) follow me the dermoepidermal junction is characteristic of bullous pemphigoid. Granular deposits of IgA in the dermal papillae is properties of dermatitis herpetiformis.<14>


Microscopy Light

Light microscopic analysis of H&E-stained samples delineates the epidermis, dermis, and subcutaneous adipose. The epidermis is conveniently visualized due to the existence of basophilic keratinocytes. Scanning across the tissue sample, one deserve to appreciate the alternative dermal papillae and rete ridges. Dermal papillae space the protrusions that dermal connective tissue right into the epidermal layer. Rete ridges space the extensions of epidermis right into the dermal layer. This undulating sample is an ext apparent in special skin of the hands and palms. Over there is no clear line of distinction between the papillary and reticular dermis. Collagen trends are greatly horizontal throughout. The superficial papillary dermis possesses thinner elastic fibers compared to the more thick elastic fibers of the reticular dermis. The papillary dermis is written of loosened connective tissue (LCT) and also is extremely vascular. The reticular dermis shows thick collagen bundles and forms the bulk of the dermal layer.

Hair follicles, glands, and also ducts can be seen throughout the epidermis, dermis, and hypodermis. Higher magnification view can further distinguish sebaceous, apocrine, and eccrine sweat glands. Meissner"s corpuscles and Pacinian corpuscles can additionally be identified upon irradiate microscopy. Pacinian corpuscles in the deep dermis or hypodermis have actually an onion-like figure on cross-sectional views. Meissner corpuscles are seen in the dermal papillae together oblong structures with neurons in a spiral orientation surrounding by a fibrous capsule.<10> 

Polarizing light microscopy is useful in the diagnosis that depositional conditions such together amyloidosis and also gout. Tissue samples, stained v Congo red dye, may be examined under polarized light, producing a characteristics apple-green birefringence of protein deposits in amyloidosis.<15> Similarly, polarized irradiate microscopy is used to differentiate urate crystal and calcium deposition.<16>


Microscopy Electron

Electron microscopy (EM) can be used to visualize the ultrastructural features of the skin. Most importantly, EM has been used to visualize the basement membrane zone the the dermoepidermal junction. EM shows ultrastructural components of hemidesmosomes, the lamina lucida (LL), the lamina densa (LD), and various anchoring fibrils.<17>


Pathophysiology

There are numerous diseases that influence the skin. The complying with discussion explains some common and uncommon diseases that affect the dermis. This discussion is no all-inclusive but demonstrates the prestige of expertise the normal structure and function of the 

Genetic illness can affect dermal structure and also function. Ehlers-Danlos syndrome is a team of hereditary connective tissue disorders resulted in by miscellaneous mutations in collagen. The mutations in dermal collagen result in skin hypermobility and fragility. Osteogenesis imperfecta is a genetic disorder of form I collagen causing diminished dermal collagen and also impaired skin elasticity.<18> Marfan"s syndrome is an additional genetic condition caused by a defect in the FBN1 gene encoding fibrillin-1 protein. When skin complaints are not required for diagnosis, patients space prone come the development of striae distensae (stretch marks) because of rapid expansion phases in adolescence.<19> These three hereditary disorders, along with other inherited diseases, may rarely cause reactive elastosis perforans serpingosa, in which transepithelial removed of elastic fibers manifests clinically as papules in one annular or serpiginous pattern.<20> 

Cushing"s syndrome, chronic glucocorticoid use, and pregnancy room other conditions causing striae distensae. Glucocorticoids inhibit fibroblasts, for this reason disrupting the synthetic of collagen and ECM material. Histology that striae distensae expose flattening of the epidermis through loss that rete ridges and changes in the style of collagen majority coupled v elastin degeneration throughout the dermis.<21> 

The overactivity that fibroblasts have been implicated in many skin-related diseases. Myofibroblasts, express alpha-smooth muscle actin (a-SMA), have to be implicated in both hypertrophic scars and also keloids.<22><23> A mindful histopathological examination is compelled to differentiate amongst keloids, hypertrophic scars, dermatofibromas, dermatofibrosarcoma protuberans, and scleroderma due to similar histopathologic findings.<24> Lichen sclerosis is an inflammation disorder involving abnormal fibroblast duty in the papillary dermis, resulting in fibrosis that the superficial dermis and also epidermis.<25> Acanthosis nigricans outcomes from increased expansion factor receptor signaling causing proliferation of epidermal keratinocytes and also dermal fibroblasts, resulting in hyperkeratosis and papillomatosis ("peaks and valleys") top top histopathology.<26><27> Researchers have likewise observed persistent activation the fibroblasts in the dermis in morphea and also nephrogenic systemic fibrosis.<28>

Aging and chronic sunlight exposure deserve to weaken the dermis. Solar elastosis is due to chronic ultraviolet (UV) radiation exposure, resulting in damages to elastic fibers. Histology discover basophilic degeneration of elastic fibers in the dermis.<29> The palliation of connective tissue in aging, usually with concomitant UV damage, reasons actinic purpura (i.e., senile purpura) wherein the dermis cannot support its vasculature. Together a result, boy trauma deserve to lead come extravasation the blood.<30> Similar manifestations may be watched in chronic glucocorticoid users. Glomus tumors can also occur within the dermis and also deeper tissues, especially within the digits and palms wherein glomus bodies are concentrated.<31>

Urticaria is an inflammation dermatosis defined by vascular hyperpermeability, leading to superficial dermal edema with resultant lymphatic dilation. The pathogenesis that urticaria often involves degranulation that mast cells and IgE-dependent pathways however is no true for every cases.<32> Mastocytosis defines a spectrum that rare conditions involving rise in mast cell within the skin and other organs. Urticaria pigmentosa is the most typical cutaneous kind of mastocytosis and predominately wake up in childhood.<33> Granulomatous diseases such as sarcoidosis, granuloma annulare, necrobiosis lipoidica, and mycobacterial epidemic (tuberculosis, leprosy) involve histiocytes within the dermis. Mycobacterium leprae infects Schwann cell of peripheral nerves top to reduced or lacking cutaneous sensation in leprosy.<34> Lymphocytic infiltration that the dermis causes diseases such as polymorphous light eruption, a usual photosensitive dermatosis.<35> Cutaneous manifestations of hematologic malignancy, such together leukemia cutis, also involve leukocytic infiltration right into the skin layers. Sweet syndrome is a rare condition associated v neutrophilia and neutrophilic infiltration right into the reticular dermis.<36> Other disorders involve the deposition of international material in ~ the dermis, such as cholesterol in xanthelasma and protein fibrils in amyloidosis.<37>

Burns and ulcers are crucial to take into consideration as the depth of burn or wound joining affects patience diagnosis and management. Partial-thickness burns, additionally known together second-degree burns, destroy the epidermis and also extend into the dermis.

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<38> Similarly, phase II press ulcers, as defined by the NPUAP, reveal the dermis.<39>