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You are watching: The hypodermis is characterized by an abundance of which tissue?

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



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


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

The dermis is divided into two layers: the papillary dermis and the reticular dermis. The papillary dermis is the superficial layer, lying deep come the epidermis. The papillary dermis is created of loose connective organization that is extremely vascular. The reticular layer is the deep layer, developing a thick layer of dense connective organization that constitutes the bulk of the dermis. 

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

The dermis houses blood vessels, nerve endings, hair follicles, and also glands. Over there are numerous cell species found within the connective tissue of the dermis, consisting of fibroblasts, macrophages, adipocytes, mast cells, Schwann cells, and also stem cells.<5> Fibroblasts space the principal cell the the dermis. Mast cells are frequently found surrounding dermal capillaries.


Skin Support and also Protection

The structure of the dermis provides a connective tissue structure for strength, flexibility, and protection that the depth anatomical structures. Collagen and also extracellular components like hyaluronic acid fortify the skin and facilitate one anchor because that the epidermis via hemidesmosomes and other adhesive basement membrane zone (BMZ) components.<6> Oxytalan fibers may additionally play a role in anchoring the epidermis. Elastic tissue also helps assistance the skin and administer flexibility. The blood vessels in the dermis are an essential for maintenance of the epidermis and also epidermal appendages. Nutrient via blood support the epidermis, hair follicles, and also sweat glands. The vascular network further permits the dermis to host an inflammatory solution via recruitment of neutrophils, lymphocytes, and also other inflammatory cells. The dermal blood supply additionally plays a role in temperature regulation questioned below. 


Vasoactive dermal vessels regulate body temperature. Committed structures called glomus bodies likewise take component in thermoregulation through AV shunt formation.<7> Glomus bodies room complexes of glomus cells, vessels, and smooth muscle cells that predominate in the digits, palms, and soles.<8> Although regularly within the dermis, eccrine sweat glands room ectoderm-derived epidermal appendages the invaginate into the deeper tissue of the dermis and subcutaneous layer.<9> 


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

Cells the the Dermis and Their Function

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

Tissue Preparation

The dermis is examined using a standard 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 making use of xylol. After, the organization sample is embedded in paraffin. ~ hardening the the paraffin medium, a microtome slices the specimen. The tissue specimen may be stained according to hematoxylin and eosin (H&E) staining protocols. 

Histochemistry and Cytochemistry

Immunofluorescence of tissue samples is critical diagnostic device in autoimmune blistering diseases such as bullous pemphigoid and dermatitis herpetiformis. Because that example, straight deposition that immunoglobulin G (IgG) and also complement (C3) along 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 also subcutaneous adipose. The epidermis is quickly visualized due to the presence of basophilic keratinocytes. Scanning throughout the tissue sample, one deserve to appreciate the alternating dermal papillae and rete ridges. Dermal papillae space the protrusions the dermal connective tissue right into the epidermal layer. Rete ridges are the extensions that epidermis right into the dermal layer. This undulating sample is much more apparent in thick skin that the hands and also palms. There is no clear line of distinction between the papillary and reticular dermis. Collagen trends are mostly horizontal throughout. The superficial papillary dermis possesses diluent elastic fibers contrasted to the thicker elastic fibers of the reticular dermis. The papillary dermis is composed of loosened connective organization (LCT) and also is extremely vascular. The reticular dermis reflects thick collagen bundles and also forms the bulk of the dermal layer.

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

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

Microscopy Electron

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


There are countless diseases that influence the skin. The adhering to discussion defines some common and uncommon illness that affect the dermis. This conversation is not all-inclusive however demonstrates the prominence of knowledge the normal structure and duty of the 

Genetic conditions can influence dermal structure and also function. Ehlers-Danlos syndrome is a group of genetic connective tissue disorders caused by various mutations in collagen. The mutations in dermal collagen result in skin hypermobility and also fragility. Osteogenesis imperfecta is a hereditary disorder of form I collagen causing reduced dermal collagen and impaired skin elasticity.<18> Marfan"s syndrome is another genetic condition caused by a defect in the FBN1 gene encoding fibrillin-1 protein. When skin complaints space not forced for diagnosis, patients are prone come the advance of striae distensae (stretch marks) due to rapid growth phases in adolescence.<19> These three hereditary disorders, together with other inherited diseases, may rarely reason reactive elastosis perforans serpingosa, in which transepithelial removed of elastic fibers manifests clinically together papules in an annular or serpiginous pattern.<20> 

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

The overactivity the fibroblasts have been implicated in countless 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 cautious histopathological examination is required to differentiate among keloids, hypertrophic scars, dermatofibromas, dermatofibrosarcoma protuberans, and also scleroderma early to comparable histopathologic findings.<24> Lichen sclerosis is an inflammatory disorder involving abnormal fibroblast function in the papillary dermis, causing fibrosis that the superficial dermis and also epidermis.<25> Acanthosis nigricans results from increased growth factor receptor signaling causing proliferation of epidermal keratinocytes and also dermal fibroblasts, resulting in hyperkeratosis and also papillomatosis ("peaks and valleys") top top histopathology.<26><27> Researchers have additionally observed persistent activation the fibroblasts in the dermis in morphea and nephrogenic systemic fibrosis.<28>

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

Urticaria is an inflammatory dermatosis characterized by vascular hyperpermeability, causing superficial dermal edema v resultant lymphatic dilation. The pathogenesis that urticaria often requires degranulation of mast cell and IgE-dependent pathways yet is not true for every cases.<32> Mastocytosis defines a spectrum of rare diseases involving boost in mast cell within the skin and also other organs. Urticaria pigmentosa is the most usual cutaneous kind of mastocytosis and predominately wake up in childhood.<33> Granulomatous diseases such as sarcoidosis, granuloma annulare, necrobiosis lipoidica, and mycobacterial infections (tuberculosis, leprosy) show off histiocytes within the dermis. Mycobacterium leprae infects Schwann cells of peripheral nerves leading to reduced or missing cutaneous emotion in leprosy.<34> Lymphocytic infiltration the the dermis causes diseases such as polymorphous irradiate eruption, a common photosensitive dermatosis.<35> Cutaneous manifestations the hematologic malignancy, such together leukemia cutis, likewise involve leukocytic infiltration into the skin layers. Sweet syndrome is a rare condition associated with neutrophilia and neutrophilic infiltration into the reticular dermis.<36> Other disorders involve the deposition of international material in ~ the dermis, together as cholesterol in xanthelasma and also protein fibrils in amyloidosis.<37>

Burns and ulcers are crucial to consider as the depth the burn or wound involvement affects patience diagnosis and management. Partial-thickness burns, likewise known as second-degree burns, damage the epidermis and extend right into the dermis.

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<38> Similarly, stage II push ulcers, as described by the NPUAP, reveal the dermis.<39>