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You are watching: Mitosis occurs in which layer of the epidermis

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


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Introduction

Skin is the biggest organ in the human body and covers the body"s whole external surface. That is comprised of 3 layers, the epidermis, dermis, and also the hypodermis, all three of i m sorry vary significantly in their anatomy and function. The skin"s framework is consisted of of an detailed network i m sorry serves as the body’s early stage barrier against pathogens, UV light, and chemicals, and mechanical injury. It additionally regulates temperature and also the amount of water released right into the environment. This post discusses the pertinent anatomical structures of the skin’s epidermal layer, the structure, function, embryology, vascular supply, innervation, operation considerations, and also clinical relevance.

Skin Thickness

The thickness of every layer that the skin varies relying on body an ar and categorized based upon the thickness of the epidermal and dermal layers. Hairless skin uncovered in the palms the the hands and also soles of the feet is thickest since the epidermis contains an extra layer, the stratum lucidum. The upper back is considered thickest based on the thickness the the dermis, however it is taken into consideration “thin skin” histologically since the epidermal thickness lacks the stratum lucidum layer and also is thinner than hairless skin.

Layers the 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 part of the epidermis).

Stratum basale, also recognized as stratum germinativum, is the deepest layer, separated from the dermis by the basement membrane (basal lamina) and also attached to the basement membrane by hemidesmosomes. The cells found in this layer space cuboidal to columnar mitotically active stem cells that room constantly producing keratinocytes. This layer likewise contains melanocytes.

Stratum spinosum, 8-10 cabinet layers, also well-known as the prickle cabinet layer contains irregular, polyhedral cells with cytoplasmic processes, sometimes called “spines”, that expand outward and also contact bordering cells through desmosomes. Dendritic cells can be found in this layer.

Stratum granulosum, 3-5 cabinet layers, contains diamond shame cells with keratohyalin granules and lamellar granules. Keratohyalin granules contain keratin precursors that at some point aggregate, crosslink, and kind bundles. The lamellar granules contain the glycolipids that obtain secreted come the surface ar of the cells and function as a glue, keeping the cells stuck together.

Stratum lucidum, 2-3 cell layers, present in more thickness skin discovered in the palms and soles, is a thin clear class consisting of eleidin i m sorry is a transformation product that keratohyalin.

Stratum corneum, 20-30 cabinet layers, is the uppermost layer, consisted of of keratin and also horny scales made up of dead keratinocytes, well-known as anucleate squamous cells. This is the layer i m sorry varies most in thickness, particularly in callused skin. Within this layer, the dead keratinocytes secrete defensins i beg your pardon are part of our first immune defense.

Cells of the Epidermis


Keratinocytes

Keratinocytes are the predominant cell type of epidermis and also originate in the basal layer, create keratin, and also are responsible because that the development of the epidermal water barrier by making and secreting lipids. Keratinocytes likewise regulate calcium absorption by the activation that cholesterol precursors through UVB irradiate to type vitamin D.

Melanocytes

Melanocytes are acquired from neural stakes cells and also primarily produce melanin, which is responsible for the colours of the skin. They are found between cells that stratum basale and produce melanin. UVB irradiate stimulates melanin secretion which is protective against UV radiation, acting as a built-in sunscreen. Melanin is produced during the switch of tyrosine come DOPA by the enzyme tyrosinase. Melanin then travels from cell to cell by a process that counts on the lengthy processes extending from the melanocytes to the neighboring epidermal cells. Melanin granules native melanocytes are transferred via the lengthy processes come the cytoplasm of basal keratinocyte. Melanin moved to bordering keratinocytes by “pigment donation”; entails phagocytosis of advice of melanocyte procedures by keratinocytes.

Langerhans’ Cells

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

Merkel Cells

Merkel cells space oval-shaped amendment epidermal cells uncovered in stratum basale, directly over the basement membrane. This cells offer a sensory role 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 are bound to adjoining keratinocytes by desmosomes and contain intermediary keratin filaments and also their membranes connect with totally free nerve end in the skin.

Dermis

The dermis is associated to the epidermis in ~ the level that the basement membrane and consists of two layers, that connective tissue, the papillary and reticular layers i beg your pardon merge together without clean demarcation. The papillary layer is the upper layer, thinner, created of loose connective tissue and also contacts epidermis. The reticular layer is the depth layer, thicker, 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.

Hypodermis

The hypodermis is deep to the dermis and also is also called subcutaneous fascia. It is the deepest class of skin and contains adipose lobules along with some skin appendages like the hair follicles, sensory neurons, and also blood vessels.


Structure and also Function

The skin has countless functions. It serves together a barrier to water, intrusion by microorganisms, mechanical and chemical trauma, and damage from UV light. The epidermal water obstacle established by the cell envelop, a layer the insoluble proteins on the inner surface of the plasma membrane. That is created by cross-linking of small proline-rich proteins and larger proteins like cystatin, desmoplakin, filaggrin and contributes to solid mechanics of barrier. And also the lipid envelope, a lipid/hydrophobic layer attached come the external surface the the plasma membrane. As 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 climate secreted by exocytosis into extracellular spaces in between the stratum granulosum and corneum. Skin is the very first site of immunological defense by the action of the Langerhans cells in the epidermis which are dendritic epidermal T lymphocytes and part of the adaptive immune system. The skin preserves the body homeostasis by regulating temperature and also water loss, while likewise serving both endocrine and also exocrine functions. The endocrine functions encompass the manufacturing of vitamin D in the keratinocytes which space responsible because that converting 7-dehydrocholesterol in the epidermis come vitamin D, v the aid of UV light from the sun. The keratinocytes express the vitamin D receptor (VDR) and also contain the enzymes necessary to transform vitamin D come its active form of 1, 25 dihydroxy vitamin D. The definition of the VDR is that stimulation of the plays a role in the proliferation the the stratum basale and also differentiation that keratinocytes as they move upwards in the epidermis. The exocrine functions of the skin space by method of the sweat and also sebaceous glands. Another important duty of the skin is a sensation to touch, heat, cold, and also pain through the action of the nociceptors. The basic appearance, turgor, and other qualities also give insight into the general health that the body. <7><8><9><10> 


Embryology

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


Blood Supply and also Lymphatics

Blood vessels and lymphatic vessels are found in the dermal great of the skin. Blood supply to the skin is an plan of two plexuses, the an initial lies between the papillary and reticular great of the dermis and also the second lie 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 essential for temperature regulation. The mechanism through which the body regulates temperature through the skin is an extremely effective and also works by raised blood flow to the skin, transferring heat from the body to the environment. The transforms in blood flow are managed by the autonomic worried system, sympathetic stimulation bring about vasoconstriction (heat retention) and also while vasodilation results in warm loss. Vasodilation of the blood ship is the an answer to enhanced body temperature and is the an outcome of inhibition that the sorry centers in the posterior hypothalamus whereas lessened body temperature will cause vasoconstriction that skin blood vessels. <13> <14>


Nerves

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


Muscles

The arrector pili muscles space bundles that smooth muscle fibers that connect to the connective tissue sheath that hair follicles. When the muscles contract, they pull the hair follicle outward bring about the hair erecting up but likewise compresses the sebaceous glands, leading to the secretion of their contents. Hair walk not exit perpendicularly, however instead at an angle. This erection of hair additionally produces goosebumps, the bumpy figure of the skin. <18>


Physiologic Variants

Skin is repeatedly shedding and also desquamating and varies slightly depending upon the human body region. Over there are an ext layers of cell in thicker hairless skin with second layer, known as the stratum lucidum. Overall, the procedure of cabinet division, desquamation, and shedding go together follows:


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

Surgical Considerations

Langer’s Lines, also known as cleavage lines, are topological lines supplied to define the anxiety of the skin, equivalent to the alignment of collagen and also elastic yarn in the reticular dermis. Operation incisions made follow me these lines, less scarring will occur. <21>


Clinical Significance

There are many clinically far-reaching aspects that the skin, including the dermatomes of the skin, skin segment divided based on the afferent nerves they are supplied through which are numbered follow to the level the spinal vertebral native which lock arise. There are 7 cervical, twelve thoracic, five lumbar, and five sacral. Specific diseases like shingles, led to by varicella-zoster infection, have actually pain sensation and also eruptive rashes the involve a dermatomal distribution. Dermatomes are beneficial in the diagnosis the vertebral spinal injury levels. As well as the dermatomes, the cell of the epidermis room susceptible to neoplastic changes resulting in assorted cancer types. Some autoimmune and immunological diseases target the desmosomes and hemidesmosomes founds in the epidermis. Certain infections can likewise disrupt the verity of the epidermis in addition to drug reaction that existing variably together well.

Squamous cell carcinoma is cancer the arises indigenous mutated keratinocytes, usually as result of UV damage in people with form I or II skin varieties (light skin, blue or eco-friendly eyes, red or blonde hair, burn and also never tan) and often appear as scaly, flaky, thick red spot that may bleed or even show up wart-like. This kind of skin cancer deserve to metastasize. Squamous cabinet carcinoma might arise native actinic keratosis, which is also caused by sun damage to the epidermal class of skin and also may have actually cutaneous horns. Basal cabinet carcinoma is a cancer the the basal great of the epidermis and is much less likely to metastasize. This type of skin cancer is an ext common in sun-exposed areas and also often show up are pearly papules top top the face, v telangiectasias and also ulcerate easily. Melanomas room cancers that the melanocytes and have a high metastatic potential, considerably mediated by the depth that the lesion. Melanomas have the right to be discovered anywhere on the body, space usually irregularly pigmented however can be amelanotic. Langerhans cabinet Histiocytosis is a type of cancer whereby Langerhans cells accumulate in the body and an outcome in the formation of granulomas, often in the bones, bring about bone pain. This granulomas can likewise appear in the skin like rashes, erythematous papules or blisters. An exciting association through this condition is the effect of the pituitary gland, which deserve to be affected and people may present with diabetes insipidus, infertility, or other endocrine illness due to poor hormones. Other serious and deadly complications are because of pancytopenia (anemia, thrombocytopenia, leukocytopenia) as a direct solution to overcrowding through the Langerhans cells. Merkel cabinet carcinoma is an uncommon cancer the the Merkel cells and also is categorized together neuroendocrine little cell carcinoma

Pemphigus vulgaris is an autoimmune disease that targets the intercellular proteins, desmosomes, that connect the keratinocytes to each other. Blisters kind within the epidermis and are quickly ruptured, causing acantholysis histologically. This condition is connected with a positive nikolsky sign, peeling far from the epidermis with rubbing of that area. Bullous Pemphigoid is an additional blistering an illness that outcomes in it s too dirty subepidermal blisters in enlarge populations, that are as result of antibodies that target the hemidesmosomes that connect the epidermis at the level that the basement membrane to the extracellular matrix of the dermis. This condition is no acantholytic and is not connected with a hopeful nikolsky sign.

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


Other Issues

The epidermal great of skin contains much the our regular flora and also the microbiome that the epidermis varies based on the body region. The microorganisms the inhabit ours skin surface is nonpathogenic and can it is in commensal or mutualistic in nature. The bacteria that tend to predominate space staphylococci epidermidis, aureus, cutibacterium acnes, Corynebacterium, Streptococcus, candida and also clostridium perfringens. Once the safety skin obstacle is altered, an infection have the right to occur.  <30>


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Figure

Histology, Trichodysplasia spinulosa, Trichodysplasia spinulosa polyomavirus, Healthy control 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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