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



Skin is the largest organ in the body and covers the body"s entire external surface. It is comprised of 3 layers, the epidermis, dermis, and also the hypodermis, all 3 of which vary significantly in your anatomy and function. The skin"s structure is consisted of of an complex network i m sorry serves together the body’s initial barrier against pathogens, UV light, and chemicals, and mechanical injury. It likewise regulates temperature and the amount of water released into the environment. This write-up discusses the relevant anatomical structures of the skin’s epidermal layer, that structure, function, embryology, vascular supply, innervation, surgical considerations, and clinical relevance.

Skin Thickness

The thickness of each layer that the skin varies depending on body an ar and categorized based upon the thickness the the epidermal and dermal layers. Hairless skin found in the palms that the hands and soles that the feet is thickest because the epidermis has an extra layer, the stratum lucidum. The upper ago is thought about thickest based upon the thickness the the dermis, but it is considered “thin skin” histologically due to the fact that the epidermal thickness lacks the stratum lucidum layer and is thinner 보다 hairless skin.

Layers of Epidermis

The class of the epidermis encompass the stratum basale (the deepest section of the epidermis), stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum (the most superficial section of the epidermis).

Stratum basale, also well-known as stratum germinativum, is the deepest layer, separated indigenous the dermis through the basement membrane (basal lamina) and also attached come the basement membrane by hemidesmosomes. The cells discovered in this layer are cuboidal to columnar mitotically active stem cell that space constantly developing keratinocytes. This layer also contains melanocytes.

Stratum spinosum, 8-10 cell layers, also known as the prickle cell layer contains irregular, polyhedral cells v cytoplasmic processes, sometimes referred to as “spines”, that expand outward and contact bordering cells by desmosomes. Dendritic cells have the right to be discovered in this layer.

Stratum granulosum, 3-5 cabinet layers, contains diamond shaped cells v keratohyalin granules and lamellar granules. Keratohyalin granules save keratin precursors that eventually aggregate, crosslink, and kind bundles. The lamellar granules contain the glycolipids that obtain secreted to the surface ar of the cell and function as a glue, keeping the cell stuck together.

Stratum lucidum, 2-3 cell layers, present in more thickness skin found in the palms and soles, is a slim clear great consisting that eleidin which is a revolution product of keratohyalin.

Stratum corneum, 20-30 cell layers, is the uppermost layer, consisted of of keratin and also horny scales consisted of of dead keratinocytes, well-known as anucleate squamous cells. This is the layer i beg your pardon varies most in thickness, especially in callused skin. In ~ this layer, the dead keratinocytes secrete defensins i m sorry are component of our an initial immune defense.

Cells of the Epidermis


Keratinocytes space the primary cell type of epidermis and also originate in the basal layer, develop keratin, and also are responsible because that the formation of the epidermal water barrier by making and also secreting lipids. Keratinocytes also regulate calcium absorb by the activation that cholesterol precursors through UVB irradiate to type vitamin D.


Melanocytes are derived from neural stakes cells and also primarily create melanin, i m sorry is responsible because that the pigment of the skin. They space found between cells the stratum basale and also produce melanin. UVB irradiate stimulates melanin cheap which is protective versus UV radiation, acting together a built-in sunscreen. Melanin is created during the counter of tyrosine come DOPA through the enzyme tyrosinase. Melanin then travels from cabinet to cabinet by a procedure that depends on the lengthy processes expanding from the melanocytes to the neighboring epidermal cells. Melanin granules native melanocytes are transferred via the long processes to the cytoplasm of basal keratinocyte. Melanin transferred to neighboring keratinocytes by “pigment donation”; requires phagocytosis of advice of melanocyte processes by keratinocytes.

Langerhans’ Cells

Langerhans cells, dendritic cells, space the skins very first line defenders and also play a significant role in antigen presentation. This cells require special stains to visualize, primarily discovered in the stratum spinosum. This cells are the mesenchymal origin, derived from CD34 optimistic stem cells of bone marrow and are part of the mononuclear phagocytic system. Castle contain Birbeck granules, tennis racket shame cytoplasmic organelles. This cells refer both MHC I and MHC II molecules, uptake antigens in skin and transport come the lymph node.

Merkel Cells

Merkel cells are oval-shaped modified epidermal cells uncovered in stratum basale, directly over the basement membrane. This cells offer a sensory duty as mechanoreceptors because that light touch, and are most populous in fingertips, though additionally found in the palms, soles, oral, and also genital mucosa. They room bound to adjoining keratinocytes through desmosomes and also contain intermediary keratin filaments and their membranes interact with free nerve endings in the skin.


The dermis is linked to the epidermis at the level that the basement membrane and also consists of two layers, the connective tissue, the papillary and reticular layers i beg your pardon merge together without clean demarcation. The papillary layer is the upper layer, thinner, written of loosened connective tissue and also contacts epidermis. The reticular layer is the depths layer, thicker, much less cellular, and also consists of thick connective tissue/ bundles of collagen fibers. The dermis dwellings the sweat glands, hair, hair follicles, muscles, sensory neurons, and also blood vessels.


The hypodermis is deep to the dermis and is likewise called subcutaneous fascia. The is the deepest layer of skin and contains adipose lobules in addition to some skin appendages choose the hair follicles, sensory neurons, and blood vessels.

Structure and Function

The skin has many functions. That serves as a barrier to water, invasion by microorganisms, mechanical and chemical trauma, and also damage native UV light. The epidermal water obstacle established by the cell envelop, a layer that insoluble protein on the inner surface of the plasma membrane. That is created by cross-linking of little proline-rich proteins and also larger proteins prefer cystatin, desmoplakin, filaggrin and contributes to strong mechanics the barrier. And the lipid envelope, a lipid/hydrophobic great attached to the external surface of the plasma membrane. Together keratinocytes in stratum spinosum create keratohyalin granules, they also produce lamellar body (containing a mixture the glycosphingolipids, phospholipids, and ceramides) assembled in ~ Golgi.  Lamellar bodies’ contents are then secreted by exocytosis into extracellular spaces between the stratum granulosum and also corneum. Skin is the an initial site of immunological defense by the action of the Langerhans cells in the epidermis which are dendritic epidermal T lymphocytes and component of the adaptive immune system. The skin preservation the bodies homeostasis by regulation temperature and water loss, while likewise serving both endocrine and exocrine functions. The endocrine functions encompass the manufacturing of vitamin D in the keratinocytes which are responsible because that converting 7-dehydrocholesterol in the epidermis come vitamin D, through the aid of UV light from the sun. The keratinocytes refer the vitamin D receptor (VDR) and also contain the enzymes necessary to convert vitamin D to its active form of 1, 25 dihydroxy vitamin D. The definition of the VDR is that stimulation of the plays a duty in the proliferation that the stratum basale and differentiation of keratinocytes as they relocate upwards in the epidermis. The exocrine features of the skin room by way of the sweat and sebaceous glands. Another important function of the skin is a sensation to touch, heat, cold, and pain through the actions of the nociceptors. The general appearance, turgor, and other qualities likewise give understanding into the general health the the body. <7><8><9><10> 


The epidermis is derived from ectodermal tissue. The dermis and hypodermis are derived from mesodermal organization from somites. The mesoderm is additionally responsible for the development of Langerhans cells. Neural comb cells, responsible for committed sensory nerve endings and melanocyte formation migrate right into the epidermis throughout epidermal development. <11><12>

Blood Supply and Lymphatics

Blood vessels and also lymphatic vessels are found in the dermal class of the skin. Blood supply to the skin is an plan of two plexuses, the an initial lies between the papillary and reticular layers of the dermis and also the second lie in between the dermis and subcutaneous tissues. It is provided to the epidermis is by way of the superficial arteriovenous plexus (subepidermal/papillary plexus). This vessels are vital for temperature regulation. The mechanism through which the human body regulates temperature through the skin is really effective and also works by boosted blood flow to the skin, transferring warmth from the human body to the environment. The changes in blood flow are controlled by the autonomic worried system, sympathetic stimulation resulting in vasoconstriction (heat retention) and also while vasodilation results in warmth loss. Vasodilation the the blood vessels is the solution to raised body temperature and is the result of inhibition the the sorry centers in the posterior hypothalamus whereas diminished body temperature will cause vasoconstriction that skin blood vessels. <13> <14>


Nerves that the skin incorporate both somatic and autonomic nerves. The somatic sensory system is responsible for pain (nociceptors), temperature, irradiate touch, discriminative touch, vibration, pressure, and proprioception medicated mainly by specialized cutaneous receptors/end organs including Merkel disks, Pacinian corpuscles, Meissner’s corpuscles, and also Ruffini corpuscles. The autonomic innervation is responsible because that the regulate of the tone of the vasculature, pilomotor stimulation at the hair root, and also sweating. The free nerve endings expand into the epidermis and also sense pain, heat, and cold. They space most many in the stratum granulosum layer and also surround many hair follicles. Merkel disks sense light touch and reach the stratum basale layer. The other nerve endings are uncovered in the deeper portions of the skin and also include the Pacinian corpuscle which senses deep pressure, Meissner’s corpuscle i beg your pardon senses low-frequency stimulation at the level of the dermal papillae, and Ruffini corpuscles which sense pressure. <15><16><17>


The arrector pili muscles space bundles the smooth muscle fibers that connect to the connective organization sheath that hair follicles. Once the muscle contract, they traction the hair follicle outward leading to the hair erecting increase but also compresses the sebaceous glands, leading to the cheap of their contents. Hair go not departure perpendicularly, however instead at an angle. This erection of hair likewise produces goosebumps, the bumpy appearance of the skin. <18>

Physiologic Variants

Skin is repeatedly shedding and also desquamating and also varies slightly depending on the human body region. There are an ext layers of cell in thicker hairless skin with second layer, recognized as the stratum lucidum. Overall, the process of cabinet division, desquamation, and shedding go as follows:

Cell division occurs in stratum basale/germinativum. One cabinet remains, an additional cell is propelled toward the surface. Basal cell begin synthesis the tonofilaments (composed of keratin) which space grouped into bundles (tonofibrils).
Cells room pushed into stratum spinosum. In the upper component of the spinous layer, cells begin to create keratohyalin granules having actually intermediate-associated proteins, filaggrin, and trichohyalin; helps aggregate keratin filaments and conversion of granular cells to cornified cells, i.e. Keratinization. Cells additionally produce lamellar bodies.
Cells are pushed into stratum granulosum and also become flattened and also diamond shaped. The cells accumulate keratohyalin granules mixed in between tonofibrils.
Cells continue to stratum corneum whereby they flatten and also lose organelles and also nuclei.  The keratohyalin granules turn tonofibrils into a homogenous keratin matrix.

Surgical Considerations

Langer’s Lines, likewise known together cleavage lines, room topological lines used to define the anxiety of the skin, matching to the alignment that collagen and also elastic fibers in the reticular dermis. Operation incisions made follow me these lines, less scarring will occur. <21>

Clinical Significance

There are countless clinically far-reaching aspects of the skin, including the dermatomes of the skin, skin segment divided based on the afferent nerves they are supplied through which are numbered according to the level of spinal vertebral indigenous which lock arise. Over there are 7 cervical, twelve thoracic, five lumbar, and five sacral. Specific diseases like shingles, caused by varicella-zoster infection, have pain sensation and also eruptive rashes the involve a dermatomal distribution. Dermatomes are advantageous in the diagnosis the vertebral spinal injury levels. As well as the dermatomes, the cells of the epidermis room susceptible come neoplastic alters resulting in various cancer types. Some autoimmune and immunological illness target the desmosomes and hemidesmosomes founds in the epidermis. Specific infections can additionally disrupt the integrity of the epidermis in addition to drug reactions that present variably as well.

Squamous cabinet carcinoma is cancer the arises indigenous mutated keratinocytes, usually because of UV damage in individuals with kind I or II skin species (light skin, blue or green eyes, red or blonde hair, burn and never tan) and often appear as scaly, flaky, thick red patches that might bleed or even show up wart-like. This form of skin cancer deserve to metastasize. Squamous cell carcinoma may arise native actinic keratosis, i beg your pardon is also caused by sun damages to the epidermal great of skin and also may have actually cutaneous horns. Basal cabinet carcinoma is a cancer that the basal great of the epidermis and is much much less likely to metastasize. This form of skin cancer is an ext common in sun-exposed areas and often show up are pearly papules ~ above the face, with telangiectasias and also ulcerate easily. Melanomas are cancers of the melanocytes and also have a high metastatic potential, considerably mediated by the depth the the lesion. Melanomas can be found anywhere top top the body, are usually irregularly pigmented yet can it is in amelanotic. Langerhans cabinet Histiocytosis is a kind of cancer where Langerhans cells accumulate in the body and an outcome in the development of granulomas, often in the bones, leading to bone pain. This granulomas can additionally appear in the skin like rashes, erythematous papules or blisters. An amazing association with this problem is the impact of the pituitary gland, which deserve to be impacted and people may current with diabetes insipidus, infertility, or various other endocrine diseases due to inadequate hormones. Various other serious and also deadly complications are as result of pancytopenia (anemia, thrombocytopenia, leukocytopenia) together a direct an answer to overcrowding by the Langerhans cells. Merkel cell carcinoma is an uncommon cancer of the Merkel cells and also is categorized as neuroendocrine small cell carcinoma

Pemphigus vulgaris is one autoimmune an illness that targets the intercellular proteins, desmosomes, that affix the keratinocytes to each other. Blisters kind within the epidermis and are quickly ruptured, bring about acantholysis histologically. This condition is linked with a positive nikolsky sign, peeling far from the epidermis with rubbing of the area. Bullous Pemphigoid is one more blistering condition that outcomes in it s too dirty subepidermal blisters in older populations, the are due to antibodies that target the hemidesmosomes that affix the epidermis at the level that the basement membrane to the extracellular procession of the dermis. This problem is no acantholytic and is not connected with a optimistic nikolsky sign.

Infections that impact the verity of the skin incorporate scalded skin syndrome caused by the exfoliative toxin released by staphylococcal aureus bacteria infection. This infection results in peeling far of the skin, hopeful nikolsky, an figure of a serious burn (very red), and also fever. Drug reactions like dress syndrome, erythema multiforme, Stevens-Johnsons syndrome, and also Toxic Epidermal Necrolysis syndrome are often connected with particular medications that include sulfa-containing drugs, NSAIDs, and also anti-seizure medications. <22><23><24><25><26><27><28><29>

Other Issues

The epidermal great of skin includes much the our common flora and the microbiome the the epidermis varies based upon the body region. The microorganisms that inhabit ours skin surface ar is nonpathogenic and also can be commensal or mutualistic in nature. The bacteria that tend to predominate room staphylococci epidermidis, aureus, cutibacterium acnes, Corynebacterium, Streptococcus, candida and also clostridium perfringens. When the security skin obstacle is altered, one infection deserve to occur.  <30>




Histology, Trichodysplasia spinulosa, Trichodysplasia spinulosa polyomavirus, Healthy manage on top, TS skin top top the bottom, Skin over view, Epidermis, Hair follicle, Acanthosis, Eosinophilic protein granules, trichohyalin, the Stain. Added by Kazem (more...)

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