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Anatomy, Skin (Integument), Epidermis Hani Yousef; Mandy Alhajj; Adegbenro O. Fakoya; Sandeep Sharma. Author Information Last Update: June 8, 2024. Introduction The skin is the largest organ in the body, covering its entire external surface. The skin has 3 layers—the epidermis, dermis, and hypodermis, which have different anatomical structures and functions (see Image. Cross Section, Layers of the Skin). The skin's structure comprises an intricate network that serves as the body's initial barrier against pathogens, ultraviolet (UV) light, chemicals, and mechanical injury. This organ also regulates temperature and the amount of water released into the environment. Skin thickness varies by body region and is influenced by the thickness of the epidermal and dermal layers. Hairless skin in the palms of the hands and soles of the feet is the thickest due to the presence of the stratum lucidum, an extra layer in the epidermis. Regions lacking this extra layer are considered thin skin. Of these regions, the back has the thickest skin because it has a thick epidermis.[1][2][3] The skin's barrier function makes it susceptible to various inflammatory and infectious conditions. In addition, wound healing, sensory changes, and cosmesis are significant surgical concerns. Understanding the skin's anatomy and function is crucial for managing conditions across all medical fields. Structure and Function Epidermis The epidermis, the skin's outermost layer, is composed of several strata and various cell types crucial for its function. Layers of the epidermis: From the deepest to the most superficial, the epidermal layers are the stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum. The stratum basale, also known as stratum germinativum, is separated from the dermis by the basement membrane (basal
lamina) and attached to it by hemidesmosomes. The cells in this layer are cuboidal to columnar, mitotically active stem cells that constantly produce keratinocytes. This layer also contains melanocytes. The stratum spinosum, comprising 8 to 10 cell layers, is also called the prickle cell layer. This layer contains irregular, polyhedral cells with cytoplasmic processes, sometimes called spines, that extend outward and contact neighboring cells by desmosomes. Dendritic cells can be found in this layer. [4][5] The stratum granulosum has 3 to 5 cell layers and contains diamond-shaped cells with keratohyalin and lamellar granules. Keratohyalin granules contain keratin precursors that aggregate, cross-link, and form bundles. The lamellar granules contain the glycolipids secreted to the cell surfaces, functioning as an adhesive to maintain cellular cohesion. The stratum lucidum comprises 2 to 3 cell layers and is present in thicker skin on the palms and soles. This thin and clear layer consists of eleidin, a transformation product of keratohyalin. The stratum corneum has 20 to 30 cell layers and occupies the uppermost epidermal layer. The stratum corneum is composed of keratin and dead keratinocytes (anucleate squamous cells) that form horny scales. This layer has the most variable thickness, especially in callused skin. Dead keratinocytes release defensins within this layer, which are part of our first line of immune defense mechanisms.[6][7] Cells of the epidermis: The epidermal cells include keratinocytes, melanocytes, and Langerhans and Merkel cells (see Image. Cells of the Epidermis). Keratinocytes are the predominant cells of the epidermis, originating from the basal layer. These cells produce keratin and lipids essential for forming the epidermal water barrier. Keratinocytes also contribute to calcium regulation by enabling UVB light absorption in the skin, which is critical for vitamin D activation. Melanocytes derive from neural crest cells and primarily synthesize melanin, the main skin pigment component. These cells are found between stratum basale cells. UVB light stimulates melanin secretion, protecting against further UV radiation exposure and acting as a built-in sunscreen. Melanin forms during the conversion of tyrosine to dihydroxyphenylalanine by the enzyme tyrosinase. Melanin then travels from cell to cell, relying on the long processes connecting the melanocytes to the neighboring epidermal cells. Melanin
Functions The skin's comprehensive roles highlight its complexity and importance in maintaining overall health and well-being. These roles are discussed below.[8][9] Barrier function: The skin has multiple protective roles, acting as a barrier against various external threats. The skin shields the body from excessive water loss or absorption, invasion by microorganisms, mechanical and chemical trauma, and UV light damage. The cell envelope establishes the epidermal water barrier, a layer of insoluble proteins on the inner surface of the plasma membrane. This barrier is formed through the cross-linking of small proline-rich proteins. Larger proteins such as cystatin, desmoplakin, and filaggrin contribute to the barrier's robust mechanics. The lipid envelope is a hydrophobic layer attached to the outer surface of the plasma membrane. Keratinocytes in the stratum spinosum produce keratohyalin granules and lamellar bodies containing a mixture of glycosphingolipids, phospholipids, and ceramides assembled within Golgi bodies. The contents of lamellar bodies are then secreted through exocytosis into the extracellular spaces between the stratum granulosum and corneum. Immunological defense: The skin plays a crucial role in both adaptive and innate immunity. In adaptive immunity, antigen-presenting cells initiate T-cell responses, leading to increased levels of helper T cells, such as TH1, TH2, or TH17. In innate immunity, the skin produces various peptides with antibacterial and antifungal properties. The skin-associated lymphoid tissue is a significant component of the immune system, aiding in preventing infections, as even minor skin breaks can lead to infection. Langerhans cells are part of the adaptive immune system, presenting foreign antigens encountered in the skin to T cells. Regulation of homeostasis: The skin plays a vital role in maintaining body temperature and water balance. This organ regulates heat exchange with the environment, particularly through the blood vessels and sweat glands. The skin manages the rate and amount of water evaporation and absorption. Endocrine and exocrine functions: Keratinocytes produce vitamin D by converting 7-dehydrocholesterol under UV light exposure. These cells also express the vitamin D receptor and contain enzymes that activate vitamin D, essential for the proliferation
and differentiation of keratinocytes. The skin's exocrine functions include temperature control by perspiration and skin protection by sebum production. Sweat and sebaceous glands are crucial to these functions. Sensory functions: The skin is equipped with nociceptors that allow for the sensation of touch, heat, cold, and pain, facilitating interaction with the environment. The skin's sensory roles are essential for an individual's movement, protection, and interaction with the environment. Diagnostic indicator: Skin characteristics such as pigmentation, smoothness, elasticity, and turgor provide insights into an individual's overall health status. Skin assessment is often a crucial part of a person's physical examination.[10][11] Cell division, desquamation, and shedding in the skin: Cell division occurs in the stratum basale. Basal cells (young keratinocytes) begin the synthesis of keratinous tonofilaments, which are grouped into bundles called tonofibrils. Older keratinocytes are then pushed into the stratum spinosum after mitosis. Skin cells begin to produce keratohyalin granules with intermediate- associated proteins, filaggrin, and trichohyalin in the upper part of the spinous layer. This process helps aggregate keratin filaments and convert granular cells into cornified cells, known as keratinization. Cells also produce lamellar bodies during this stage. Keratinocytes continue to move into the stratum granulosum afterward, where they become flattened and diamond-shaped. The cells accumulate keratohyalin granules mixed between tonofibrils. Keratinocytes then continue to the stratum corneum, flattening and losing organelles and nuclei. The keratohyalin granules turn tonofibrils into a homogenous keratin matrix. Cornified cells reach the surface and are desquamated when desmosomes disintegrate. The proteinase activity of kallikrein- related serine peptidase is triggered by lowered pH near the surface. The processes of skin shedding and desquamation vary slightly by body region. Hairless skin comprises more layers, with the addition of the stratum lucidum. Thus, keratinocytes in body regions with hairless skin go through more layers before reaching the surface.[12][13]
and around most hair follicles. Merkel disks sense light touch and reaches the stratum basale layer. The other nerve endings are found in the deeper portions of the skin and include the Pacinian, Meissner, and Ruffini corpuscles. The Pacinian corpuscles sense deep pressure. The Meissner corpuscles sense low-frequency stimulation at the level of the dermal papillae. The Ruffini corpuscles sense pressure.[18][19][20] Muscles The arrector pili muscles are bundles of smooth muscle fibers attached to the connective tissue sheath of hair follicles. Contraction of these muscles pulls the hair follicle outward, erecting the hair. The arrector pili also compress the sebaceous glands, facilitating sebum secretion. Hair does not exit perpendicularly but at an angle. The erection of hair, known as piloerection, produces goosebumps, giving the skin a bumpy appearance when exposed to cold temperatures.[21] Studies show that piloerection contributes to thermoregulation and stem cell growth.[22] Surgical Considerations Langer lines, also known as cleavage lines, are topological lines used to define skin tension. These lines correspond to the alignment of collagen and elastic fibers in the reticular dermis. Less scarring occurs if surgical incisions are made along these lines. [23] Clinical Significance The skin's clinical significance spans all medical disciplines. A few are discussed below. Dermatomes Dermatomes are skin segments divided based on afferent nerve distribution, numbered according to spinal vertebral levels. Spinal nerves comprise 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerve. Diseases such as shingles caused by varicella-zoster infection manifest pain and rashes in dermatomal patterns. Dermatomes also aid in localizing spinal injuries.
Squamous Cell Carcinoma Squamous cell carcinoma is a malignancy arising from mutated keratinocytes, typically due to UV damage in individuals with type I or II skin types. These individuals typically have light skin, blue or green eyes, and red or blonde hair and burn without tanning. The lesions often appear as scaly, flaky, thick red patches that may bleed. Some squamous cell carcinoma tumors resemble warts. This type of skin cancer can metastasize. Squamous cell carcinoma often arises from actinic keratoses—premalignant lesions with cutaneous horns developing from chronic UV damage.[24] Basal Cell Carcinoma Basal cell carcinoma is a malignant neoplasm of the basal layers of the epidermis. Unlike squamous cell carcinoma, it is much less likely to metastasize. This type of skin cancer is more common in sun-exposed areas, often appearing as pearly papules on the face, with telangiectasias and a great tendency to ulcerate. Melanoma Melanoma is a highly invasive malignant melanocyte tumor that is fatal but rarer than skin squamous cell carcinoma and basal cell carcinoma. This neoplasm's high metastatic potential is significantly mediated by lesion depth. Melanoma can be found anywhere on the body and is typically irregularly pigmented but can be amelanotic. [25] Langerhans Cell Histiocytosis Langerhans cell histiocytosis is a type of cancer in which Langerhans cells accumulate in the body and form granulomas, often in the bones, causing bone pain. These granulomas can also appear in the skin, producing rashes, erythematous papules, or blisters (see Image. Histology, Trichodysplasia Spinulosa). Notably, Langerhans cell histiocytosis can affect the pituitary gland, leading to diabetes insipidus, infertility, or other endocrine disorders due to hormone deficiencies. Pancytopenia is a potentially fatal Langerhans cell histiocytosis complication, manifesting with anemia, thrombocytopenia, and leukocytopenia, caused by overcrowding of Langerhans cells in the bone marrow.[26]
certain medications, including sulfa-containing drugs, nonsteroidal anti-inflammatory drugs, and antiepileptics.[31][32] Other Issues The epidermis contains much of our normal flora, with the microbiome varying by body region. The microorganisms inhabiting our skin surfaces are nonpathogenic and can be commensal or mutualistic. The bacteria that tend to predominate are Staphylococcus epidermidis and S aureus , Cutibacterium acnes , Corynebacterium , Streptococcus , Candida , and Clostridium perfringens. However, infections may occur when the protective skin barrier is altered or breached.[33] Citation: Yousef H, Alhajj M, Sharma S. Anatomy, Skin (Integument), Epidermis. In: StatPearls. StatPearls Publishing, Treasure Island (FL); 2023. PMID: 29262154. https://europepmc.org/article/nbk/nbk470464#NBK470464_ai NCBI Bookshelf. A service of the National Library of Medicine, National Institutes of Health. StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-.
Physiology, Integument
Authors
Joyce Y. Kim^1 ; Harry Dao^2.
Affiliations
(^1) University of California Riverside School of Medicine (^2) Loma Linda University Last Update: May 1, 2023. Introduction The integumentary system is the largest organ of the body that forms a physical barrier between the external environment and the internal environment that it serves to protect and maintain. The integumentary system includes the epidermis, dermis, hypodermis, associated glands, hair, and nails. In addition to its barrier function, this system performs many intricate functions such as body temperature regulation, cell fluid maintenance, synthesis of Vitamin D, and detection of stimuli. The various components of this system work in conjunction to carry out these functions—for example, body temperature regulation occurs through thermoreceptors that lead to the adjustment of peripheral blood flow, degree of perspiration, and body hair. Organ Systems Involved Components of the Integumentary System Skin : The skin is made up of two layers—the superficial epidermis and the deeper dermis. The epidermis is the tough outer layer that acts as the first line of defense against the external environment. It is composed of stratified squamous epithelial cells that further break down into four to five layers. From superficial to deep, the primary layers are the stratum corneum, stratum granulosum, stratum spinosum, and stratum basale. In the palms and soles, where the skin is thicker, there is an additional layer of skin between the stratum corneum and stratum granulosum called the stratum lucidum. The epidermis regenerates from stem cells located in the basal layer that grow up towards the corneum. The epidermis itself is devoid of blood supply and derives its nutrition from the underlying dermis. The dermis is the underlying connective tissue framework that supports the epidermis. It further subdivides into two layers—the superficial papillary dermis and the deep reticular layer. The papillary layer forms finger-like projections into the epidermis, known as dermal papillae, and consists of highly vascularized, loose connective tissue. The reticular layer has dense connective tissue that forms a strong network.[1] The dermis as a whole contains blood and lymph vessels, nerves, sweat glands, hair follicles, and various other structures embedded within the connective tissue. Hypodermis : The hypodermis lies between the dermis and underlying organs. It is commonly referred to as subcutaneous tissue and is composed of loose areolar tissue
which are prone to repeated trauma by creating a hard covering, and hairs throughout the body filter harmful particles from entering the eyes, ears, nose, etc. Immunity : The skin is the body’s first line of defense as it acts as the physical barrier that prevents direct entry of pathogens. Cells are connected through junction proteins with reinforcement by keratin filaments.[9] Antimicrobial peptides (AMPs) and lipids on the skin also act as a biomolecular barrier that disrupts bacterial membranes. AMPs, such as defensins and cathelicidins, are produced by various cells in the skin, such as dendritic cells, macrophages, glands, etc., and are activated by proteolytic cleavage with stimulation. Lipids, such as sphingomyelin and glucosylceramides, are stored in lamellar bodies found in the stratum corneum and display antimicrobial activity.[9] An additional aspect of the skin’s immunity lies in the resident immune cells. Both myeloid and lymphoid cells are present in the skin, and some, such as the Langerhans cells or dermal dendritic cells, possess the capability to travel to the periphery and activate the greater immune system.[9] Wound healing : When our body undergoes trauma with a resulting injury, the integumentary system orchestrates the wound healing process through hemostasis, inflammation, proliferation, and remodeling.[9] Hemostasis occurs through tissue factor located in subendothelial spaces of the skin, which triggers the coagulation cascade to form a fibrin clot. In the following inflammatory phase, immune cells such as neutrophils and monocytes will infiltrate the injury site to attack pathogens and clear out debris. The proliferative phase involves the multiplication of resident cells such as keratinocytes and fibroblasts that contribute to the formation of granulation tissue. Through a matrix of immune cells and the eventual formation of a collagen network by fibroblasts and myofibroblasts, the new extracellular matrix forms.[9] The final remodeling phase consists of apoptosis as cells are no longer needed and excess structures are broken down in efforts to restore the original architecture. Macrophages secrete matrix metalloproteases that remove excess collagen, and remaining immature collagen matures to finalize the extracellular matrix.[9] Vitamin D synthesis: The primary sources of vitamin D are sun exposure and oral intake. With ultraviolet sunlight exposure, 7-dehydrocholesterol converts to vitamin D3 (cholecalciferol) in the skin. Cholecalciferol is then hydroxylated in the liver, then kidney into its active metabolite form, 1,25-dihydroxy vitamin D (calcitriol).[10] This metabolite ultimately leads to increased calcium absorption in the gut and is crucial for bone health. Regulation of body temperature: The skin has a large surface area that is highly vascularized, which allows it to conserve and release heat through vasoconstriction and vasodilation, respectively. When body temperatures rise, blood vessels dilate to
increase blood flow and maximize the dissipation of heat.[11] In conjunction with this method, the evaporation of sweat secreted by the skin allows for greater heat loss. The hair on the body also affects the regulation of body temperature as erect hair can trap a layer of heat close to the skin. Various inputs from central and skin thermoreceptors provide fine-tuning for this thermoregulatory system. Sensation : Skin innervation is by various sensory nerve endings that discriminate pain, temperature, touch, and vibration. Mediation of innocuous touch in glabrous skin by four types of mechanoreceptors—Meissner corpuscle, Pacinian corpuscle, Ruffini endings, and Merkel cells.[12] Meissner corpuscles can detect movement across the skin, Pacinian corpuscles detect high-frequency vibration, Ruffini endings detect stretch, and Merkel cells aid in spatial imaging. In hairy skin, tactile stimuli are picked up by three types of hair follicles and their associated longitudinal and circumferential lanceolate endings.[12] Noxious stimuli in both glabrous and hairy skin are detectable by free nerve endings located in the epidermis.[12] Each type of receptor and nerve fiber varies in its adaptive and conductive speeds, leading to a wide range of signals that can be integrated to create an understanding of the external environment and help the body to react appropriately. Pathophysiology Pathology Given that the integumentary system has direct exposure to external threats such as physical trauma, radiation, extreme temperatures, microorganisms, etc., it can fall susceptible to wounds, infections, burns, cancers, and more. The integumentary system is unique in that pathologic conditions are often directly visible to patients, and at times the system reflects pathologic conditions that may be occurring internally. The following are common conditions that can appear throughout components of the integumentary system: Skin: Acne – Acne is a very common condition that involves inflammation of the pilosebaceous unit caused by the overproduction of keratin within hair follicles, increased sebum production, and Cutibacterium acnes mediated inflammation. [13] Acne can have varying morphologies, including comedones (open and closed), papules, nodules, and pustules, that all vary in appearance and size. Various factors correlate with the development of acne, such as skin trauma, diet, and stress.[14] In women, hormonal acne is characterized by flares involving the jawline, characteristically flaring with menstrual cycles. Increased androgen circulation also contributes to acne, as sebaceous glands produce sebum in response to androgens, providing a growth medium for C. acnes and increasing inflammation.[13] Atopic dermatitis – More commonly referred to as eczema, this is a chronic condition that affects both children and adults. Multiple factors such as defects in epidermal junctions, reduced innate immunity in the skin, and genetics appear to contribute to the
Burns —Burns result from excessive heat, radiation, or chemical exposure, and grading the severity of the burn is by the depth and area of skin involvement. Burns are treated as emergencies, as severe burns can lead to dehydration, sepsis, and death. [26] Burn depth can classify as follows [27]: Superficial: involves only the epidermal layer and does not blister. Lesions are painful, dry, red, and blanch. Injuries generally heal without scarring. Partial-thickness: involves the epidermis and dermis partially. This type of burn can further subcategorize into superficial and deep, depending on the extent of dermis involvement. Superficial partial-thickness lesions form blisters, are painful, blanch with pressure, and weep. Deep partial-thickness burns damage hair follicles and glandular tissue. They are painful to pressure only, do not blanch, and have mottled colorization. They can cause hypertrophic scarring and functional impairment with delayed healing. Full-thickness: extend through all layers of the dermis and often subcutaneous tissue. The lesions are generally dry without blistering and do not blanch with pressure. Eschar (dead dermis) may be present and can compromise a limb if circumferential. Fourth degree: these are the most severe burns that extend beyond the skin into soft tissue and can involve any underlying structures. Hair Alopecia areata – This is an autoimmune condition that involves loss of immune privilege at the hair follicle in addition to T cell-mediated attack on cells of the hair bulb, leading to hair follicles that transition from the growth phase (anagen) to nonproliferative (catagen) and resting (telogen) phases. This situation results in hair shedding in any hair-bearing area, though it most commonly occurs on the scalp. It is a nonscarring condition that can sometimes self-remit with spontaneous hair regrowth, sometimes even without treatment. There are several patterns of hair loss, such as patchy, ophiasis, sisaipho, and diffuse, with patchy alopecia being the most common subtype.[28] Folliculitis – Folliculitis is inflammation of the hair follicle that presents clinically with follicular pustules and erythematous papules. It may have an infectious or noninfectious etiology and can be due to bacterial, fungal, viral, or parasitic infections. A bacterial infection is the most common etiology, with Staphylococcus aureus being the most common causative bacteria. People will generally experience pruritus over hair-bearing areas and can occasionally have painful pustules and papules. Folliculitis barbae is a subtype of bacterial folliculitis that affects deep portions of the hair follicles in the beard areas.[29] Male pattern balding – This is a condition with a genetic predisposition in which hair loss occurs in an androgen-dependent manner. Hair follicles undergo follicular miniaturization, which is shortening of the growth phase (anagen), and transition from
dark terminal hairs to thin vellus hairs. This process initiates when dihydrotestosterone binds to androgen receptors in the hair follicle and progresses as an increasing number of follicles are affected.[30] Nails Onychomycosis – Onychomycosis is a fungal infection of the toenails or fingernails and can result from dermatophytes, yeasts, and non-dermatophyte molds. The condition is acquired through direct contact, and a compromised nail barrier increases the chances of infection.[31] The common clinical presentation involves nail discoloration, subungual hyperkeratosis, onycholysis, and splitting or destruction of the nail plate, dependent on the specific subtype.[32] Pitting – Nail pitting occurs due to focal abnormal keratinization of the nail matrix that results in irregular, deep pits within the nail plate as it grows beyond the cuticle. It can affect a single nail or multiple, can involve the fingernails and/or toenails. It presents in conditions such as psoriasis, eczema, and alopecia areata.[33][34] Koilonychia – Also called spoon nail, this condition involves the upward curving of the distal nail plate that gives the appearance of a spoon. It has been associated with iron deficiency anemia but can be due to idiopathic changes. Clubbing – Digital clubbing is characterized by increased nail plate curvature and thickness of the distal fingertip. Clinically, there is flattening of the angle between the nail plate and the nail fold on the side view. It is caused by platelet precursors that fail fragmentation and later get trapped in the distal digit vasculature. There they will release platelet-derived growth factor and vascular endothelial growth factor, which results in clubbing. It is the most common manifestation of hypertrophic osteoarthropathy and correlates with many systemic conditions.[35] Glands Seborrheic dermatitis - Seborrheic dermatitis is a form of chronic dermatitis with unknown pathogenesis that tends to occur in regions with sebaceous glands, such as the scalp, external ears, and center of the face. It presents clinically with erythematous plaques with a yellowish scale and often appears as dandruff when located on the scalp. The cause and predilection for sebaceous glands are not well understood, though studies have suggested that the fungus Malassezia and its byproducts may play a role in the pathogenesis.[36][37][38] Hyperhidrosis – Hyperhidrosis is excessive secretion of sweat from eccrine glands with possible apocrine gland involvement in axillary hyperhidrosis.[39] Pathogenesis is an abnormal central response to normal emotional stress, which leads to increased sympathetic signaling to endocrine glands through cholinergic autonomic neurons leading to sweating beyond the physiological need for temperature regulation. [40] Clinical Significance
Integumentary System - Cleveland Clinic
Your integumentary system is your body’s outer layer. It consists of your skin, hair, nails and
glands. These organs and structures are your first line of defense against bacteria and help
protect you from injury and sunlight. Your integumentary system works with other systems
in your body to keep it in balance.
Overview
Anatomy of the integumentary system, including human skin and hair.
Your integumentary system consists of your hair, skin and nails. It’s your body’s outer layer
and first line of defense against bacteria and injury.
What is the integumentary system?
Your integumentary system is your body’s outer layer. It’s made up of your skin, nails, hair
and the glands and nerves on your skin. Your integumentary system acts as a physical barrier
— protecting your body from bacteria, infection, injury and sunlight. It also helps regulate
your body temperature and allows you to feel skin sensations like hot and cold.
What makes up the integumentary system?
Your integumentary system is an organ that consists of a few main structures: skin, nails, hair
and glands, along with the nerves and blood vessels that support them.
Skin
Your skin is the largest and heaviest organ in your body. It weighs about six pounds (or
more) and is approximately 2 millimeters thick — thinner on sensitive areas like eyelids, and
thicker on surfaces that take more stress, like the soles of your feet. One inch of your skin
contains nearly 19 million cells.
Your skin is composed of three layers, with nerves that recognize different sensations in each
layer:
Epidermis: The top layer of your skin. This is the part of your skin that you can see and
touch. It’s made up of three types of cells: melanocytes, keratinocytes and Langerhans. It
gives your skin its color and provides a waterproof barrier.
Dermis: The middle layer of your skin. This layer is the thickest. It contains sweat and oil
glands and hair follicles.
Hypodermis: The bottom layer of your skin. It’s the fatty layer of your skin that helps
insulate your body.
Nails
Your nails protect the ends of your fingers and toes. The anatomy of your nail consists of:
Nail plate: The hard part of your nail you can see.
Nail bed: The skin under your nail plate.
Cuticle: The thin skin at the base of your nail plate.
Matrix: The “root” of your nail responsible for making it grow.
Lunula: The white, moon-shaped part of your nail plate.
Hair
Our hair does more than help us look nice. The hair on your head helps keep heat in your
body. Your eyelashes and eyebrows help protect your eyes from dirt and water.
Your hair is made of a protein called keratin. Your hair consists of three parts: the shaft,
follicle and bulb.
Hair shaft: The part of your hair you can see, touch and style.
Hair follicle: The tube-like structure that keeps your hair in your skin.
Hair bulb: Located under your skin and responsible for hair growth.
Goosebumps are caused by your integumentary system. We all have hair erector muscles
connected to our hair follicles and skin. When it contracts, it makes your hair stand up. The
“goosebumps” are what we see when these tiny muscles contract.
Glands
Glands are found throughout your skin. They release materials like water, salt or oil from
under your skin to the surface of your skin. Your integumentary system consists of the
following glands:
