dermis | anatomy | Britannica.com anatomy ligament Dermis, also called corium, the thicker, deeper layer of the skin underlying the epidermis and made up of connective tissue . It is present in varying degrees of development among various vertebrate groups, being relatively thin and simple in aquatic animals and progressively thicker and more complex in terrestrial species. The dermis from its earliest evolutionary appearance has been a depository of bone , as expressed in dermal armour (primitive fishes), scales (fishes and certain amphibians), and plates (crocodile, lizard, turtle, armadillo). The fin rays of fishes are dermal derivatives, as are many types of pigment cells. The dermis of mammals is of greater thickness relative to the epidermis than is that of other vertebrates, partly because it contains abundant collagenous connective tissue. When treated with tannic acid, the dermis becomes leather . In humans the dermis projects into the overlying epidermis in ridges called papillae (see video). Nerves that extend through the dermis and end in the papillae are sensitive to heat , cold, pain, and pressure.

Sweat glands and oil glands lie in the deeper stratum reticulare , as do the bases of hair follicles, the nail beds, and blood and lymph vessels. Dermal anatomy. in animal development: The epidermis and its outgrowths The epidermis is only the superficial layer of the skin, which is reinforced by the dermis, a connective tissue layer of a much greater thickness. The cells of the dermis are derived from mesoderm and neural-crest cells. In particular the pigment cells found in the dermis of fishes, amphibians, and reptiles are of neural-crest origin. The pigment in the skin of birds and mammals (and also in... in prenatal development: Integumentary system ...superficial cells and downy hairs mingle with a greasy glandular secretion and smear the skin in the late fetal months; the pasty mass is called vernix caseosa. The deep layer of the skin, or dermis, is a fibrous anchoring bed differentiated from mesoderm. In the later fetal months the plane of union between epidermis and dermis becomes wavy. The permanently ridged patterns are notable at... 7 References found in Britannica Articles Assorted References Corrections?

Updates? Help us improve this article! Contact our editors with your feedback. MEDIA FOR: You have successfully emailed this. Error when sending the email. Try again later. Edit Mode Submit Tips For Editing We welcome suggested improvements to any of our articles. You can make it easier for us to review and, hopefully, publish your contribution by keeping a few points in mind. Encyclopædia Britannica articles are written in a neutral objective tone for a general audience. You may find it helpful to search within the site to see how similar or related subjects are covered. Any text you add should be original, not copied from other sources. At the bottom of the article, feel free to list any sources that support your changes, so that we can fully understand their context. (Internet URLs are the best.) Your contribution may be further edited by our staff, and its publication is subject to our final approval. Unfortunately, our editorial approach may not be able to accommodate all contributions. Submit Thank You for Your Contribution! Our editors will review what you've submitted, and if it meets our criteria, we'll add it to the article.

Please note that our editors may make some formatting changes or correct spelling or grammatical errors, and may also contact you if any clarifications are needed. Uh Oh There was a problem with your submission. Please try again later. Close Date Published: April 07, 1999 URL: Access Date: January 18, 2017 Share Skin Anatomy: Overview, Epidermis, Dermis Skin Anatomy Author: Bardia Amirlak, MD; Chief Editor: Gregory Gary Caputy, MD, PhD, FICS more... Share Overview Overview The skin covers the entire external surface of the human body and is the principal site of interaction with the surrounding world. It serves as a protective barrier that prevents internal tissues from exposure to trauma, ultraviolet (UV) radiation, temperature extremes, toxins, and bacteria. Other important functions include sensory perception, immunologic surveillance, thermoregulation, and control of insensible fluid loss. The integument consists of 2 mutually dependent layers, the epidermis and dermis, which rest on a fatty subcutaneous layer, the panniculus adiposus.

(See the image below.) The epidermis is derived primarily from surface ectoderm but is colonized by pigment-containing melanocytes of neural crest origin, antigen-processing Langerhans cells of bone marrow origin, and pressure-sensing Merkel cells of neural crest origin. The dermis is derived primarily from mesoderm and contains collagen, elastic fibers, blood vessels, sensory structures, and fibroblasts. [ 1 ] Anatomy of the skin. View Media Gallery During the fourth week of embryologic development, the single cell thick ectoderm and underlying mesoderm begin to proliferate and differentiate. The specialized structures formed by the skin, including teeth, hair, hair follicles, fingernails, toenails, sebaceous glands, sweat glands, apocrine glands, and mammary glands also begin to appear during this period in development. Teeth, hair, and hair follicles are formed by the epidermis and dermis in concert, while fingernails and toenails are formed by the epidermis alone.

Hair follicles, sebaceous glands, sweat glands, apocrine glands, and mammary glands are considered epidermal glands or epidermal appendages, because they develop as downgrowths or diverticula of the epidermis into the dermis. [ 1 , 2 ] The definitive multi-layered skin is present at birth, but skin is a dynamic organ that undergoes continuous changes throughout life as outer layers are shed and replaced by inner layers. Skin also varies in thickness among anatomic location, sex, and age of the individual. This varying thickness primarily represents a difference in dermal thickness, as epidermal thickness is rather constant throughout life and from one anatomic location to another. Skin is thickest on the palms and soles of the feet (1.5 mm thick), while the thinnest skin is found on the eyelids and in the postauricular region (0.05 mm thick). Male skin is characteristically thicker than female skin in all anatomic locations. Children have relatively thin skin, which progressively thickens until the fourth or fifth decade of life when it begins to thin.

This thinning is also primarily a dermal change, with loss of elastic fibers, epithelial appendages, and ground substance. [ 3 ] Next: Epidermis The epidermis contains no blood vessels and is entirely dependent on the underlying dermis for nutrient delivery and waste disposal via diffusion through the dermoepidermal junction. The epidermis is a stratified, squamous epithelium that consists primarily of keratinocytes in progressive stages of differentiation from deeper to more superficial layers. The named layers of the epidermis include the stratum germinativum, stratum spinosum, stratum granulosum, and stratum corneum. Keratinocytes The stratum germinativum, or the basal layer, is immediately superficial to the dermoepidermal junction. This single cell layer of keratinocytes is attached to the basement membrane via hemidesmosomes. As keratinocytes divide and differentiate, they move from this deeper layer to the more superficial layers. Once they reach the stratum corneum, they are fully differentiated keratinocytes devoid of nuclei and are subsequently shed in the process of epidermal turnover.

Cells of the stratum corneum are the largest and most abundant of the epidermis. This layer ranges in thickness from 15-100 or more cells depending on anatomic location and is the primary protective barrier from the external environment. Melanocytes Melanocytes, derived from neural crest cells, primarily function to produce a pigment, melanin, which absorbs radiant energy from the sun and protects the skin from the harmful effects of UV radiation. Melanin accumulates in organelles termed melanosomes that are incorporated into dendrites anchoring the melanosome to the surrounding keratinocytes. Ultimately, the melanosomes are transferred via phagocytosis to the adjacent keratinocytes where they remain as granules. Melanocytes are found in the basal layer of the epidermis as well as in hair follicles, the retina, uveal tract, and leptomeninges. These cells are the sites of origin of melanoma . In areas exposed to the sun, the ratio of melanocytes to keratinocytes is approximately 1:4. In areas not exposed to solar radiation, the ratio may be as small as 1:30.

Absolute numbers of melanosomes are the same among the sexes and various races. Differing pigmentation among individuals is related to melanosome size rather than cell number. Sun exposure, melanocyte-stimulating hormone (MSH), adrenocorticotropic hormone (ACTH), estrogens, and progesterones stimulate melanin production. With aging, a decline is observed in the number of melanocytes populating the skin of an individual. Since these cells are of neural crest origin, they have no ability to reproduce. Langerhans cells Langerhans cells originate from the bone marrow and are found in the basal, spinous, and granular layers of the epidermis. They serve as antigen-presenting cells. They are capable of ingesting foreign antigens, processing them into small peptide fragments, binding them with major histocompatibility complexes, and subsequently presenting them to lymphocytes for activation of the immune system. An example of activation of this component of the immune system is contact hypersensitivity. Merkel cells Merkel cells, also derived from neural crest cells, are found on the volar aspect of digits, in nail beds, on the genitalia, and in other areas of the skin.

These cells are specialized in the perception of light touch. [ 1 , 3 ] Previous Next: Dermis The primary function of the dermis is to sustain and support the epidermis. The dermis is a more complex structure and is composed of 2 layers, the more superficial papillary dermis and the deeper reticular dermis. The papillary dermis is thinner, consisting of loose connective tissue containing capillaries, elastic fibers, reticular fibers, and some collagen. The reticular dermis consists of a thicker layer of dense connective tissue containing larger blood vessels, closely interlaced elastic fibers, and coarse bundles of collagen fibers arranged in layers parallel to the surface. The reticular layer also contains fibroblasts, mast cells, nerve endings, lymphatics, and epidermal appendages. Surrounding the components of the dermis is the gel-like ground substance, composed of mucopolysaccharides (primarily hyaluronic acid), chondroitin sulfates, and glycoproteins. The deep surface of the dermis is highly irregular and borders the subcutaneous layer, the panniculus adiposus, which additionally cushions the skin.

Fibroblasts The fibroblast is the major cell type of the dermis. These cells produce and secrete procollagen and elastic fibers. Procollagen is terminally cleaved by proteolytic enzymes into collagen that aggregates and becomes cross-linked. These tightly cross-linked collagen fibers provide tensile strength and resistance to shear and other mechanical forces. Collagen makes up 70% of the weight of the dermis, primarily Type I (85% of the total collagen) and Type III (15% of the total collagen). Elastic fibers constitute less than 1% of the weight of the dermis, but they play an enormous functional role by resisting deformational forces and returning the skin to its resting shape. [ 1 ] Previous Next: Dermoepidermal Junction The dermoepidermal junction is an undulating basement membrane that adheres the epidermis to the dermis. It is composed of 2 layers, the lamina lucida and lamina densa. The lamina lucida is thinner and lies directly beneath the basal layer of epidermal keratinocytes. The thicker lamina densa is in direct contact with the underlying dermis.

These structures are the target of immunologic injury in bullous pemphigoid and epidermolysis bullosa. Dermal papillae from the papillary dermis contain a plexus of capillaries and lymphatics oriented perpendicular to the skin surface. These fingerlike projections are surrounded by similar projections of the epidermis. This highly irregular junction greatly increases the surface area over which oxygen, nutrients, and waste products are exchanged between the dermis and the avascular epidermis. [ 1 ] Previous Next: Epidermal Appendages Epidermal appendages are intradermal epithelial structures lined with epithelial cells with the potential for division and differentiation. These are important as a source of epithelial cells, which accomplish reepithelialization should the overlying epidermis be removed or destroyed in situations such as partial thickness burns , abrasions, or split-thickness skin graft harvesting. Epidermal appendages include the following: Sebaceous glands Next: Cutaneous Blood Supply Cutaneous vessels ultimately arise from underlying named source vessels. Each source vessel supplies a 3-dimensional vascular territory from bone to skin termed an angiosome.

Adjacent angiosomes have vascular connections via reduced caliber (choke) vessels or similar caliber (true) anastomotic vessels. The cutaneous vessels originate either directly from the source arteries (septocutaneous or fasciocutaneous perforators) or as terminal branches of muscular vessels (musculocutaneous perforators). During their course to the skin, the cutaneous vessels travel within or adjacent to the connective tissue framework and supply branches to each tissue with which they come into close contact (bone, muscle, fascia, nerve, fat). They emerge from the deep fascia in the vicinity of the intermuscular or intramuscular septa or near tendons and travel toward the skin, where they form extensive subdermal and dermal plexuses. The dermis contains horizontally arranged superficial and deep plexuses, which are interconnected via communicating vessels oriented perpendicular to the skin surface. Cutaneous vessels ultimately anastomose with other cutaneous vessels to form a continuous vascular network within the skin. Clinically, this extensive horizontal network of vessels allows for random skin flap survival.

[ 6 , 7 , 8 ] Thermoregulation In addition to the skin's natural heat conductivity and loss of heat from the evaporation of sweat, convection from cutaneous vessels is a vital component of thermoregulation. Cutaneous blood flow is 10-20 times that required for essential oxygenation and metabolism, and large amounts of heat can be exchanged through the regulation of cutaneous blood flow. The thermoregulatory center in the hypothalamus controls vasoconstriction and vasodilatation of cutaneous vessels through the sympathetic nervous system. Previous Next: Lymphatics Skin lymphatics parallel the blood supply and function to conserve plasma proteins and scavenge foreign material, antigenic substances, and bacteria. Blind-ended lymphatic capillaries arise within the interstitial spaces of the dermal papillae. These unvalved, superficial dermal vessels drain into valved deep dermal and subdermal plexuses. These then coalesce to form larger lymphatic channels, which course through numerous filtering lymph nodes on their way to join the venous circulation near the subclavian vein – internal jugular vein junction bilaterally.

Previous Next: Skin Innervation Sensory perception is critically important in the avoidance of pressure, mechanical or traumatic forces, and extremes of temperature. Numerous specialized structures are present in the skin to detect various stimuli. As previously mentioned, Merkel cells of the epidermis detect light touch. Meissner corpuscles also detect light touch. These are found in the dermal papillae and are most concentrated in the fingertips. Pacini corpuscles are found deep within the dermis or even in the subcutaneous tissue. These structures are specialized to detect pressure. Pain is transmitted through naked nerve endings located in the basal layer of the epidermis. Krause bulbs detect cold, whereas Ruffini corpuscles detect heat. Heat, cold, and proprioception also are located in the superficial dermis. Cutaneous nerves follow the route of blood vessels to the skin. The area supplied by a single spinal nerve, or a single segment of the spinal cord, is termed a dermatome. Adjacent dermatomes may overlap considerably, which is important to note when performing field blocks with local anesthesia. [ 1 , 9 ] Previous Next: Surface Anatomy Lines and creases are evident over major and minor joints.

Skin contraction produces wrinkles and creases that lie perpendicular to the underlying muscular vector force. Relaxed skin tension lines (RSTL), however, are formed during relaxation and often follow a different direction than age and contracting wrinkles. (See the image below.) Relaxed skin tension lines are created by the natural tension on the skin from underlying structures. [ 10 ] Four main facial lines show the direction of relaxed skin tension lines. Contributor Information and Disclosures Author Bardia Amirlak, MD Assistant Professor of Plastic Surgery, Director of Residency Cosmetic Clinic, Director of Plastic Surgery Global Health Program, University of Texas Southwestern Medical Center at Dallas; Chief of Hand and Peripheral Nerve Surgery, Dallas Veterans Affairs Medical Center Bardia Amirlak, MD is a member of the following medical societies: American College of Surgeons , American Society of Plastic Surgeons , American Society of Reconstructive Transplantation , Kleinert Society Disclosure: Nothing to disclose. Coauthor(s) Ladan Shahabi, MD Clinical Assistant Professor, Department of Dermatology, New York University Ladan Shahabi, MD is a member of the following medical societies: American Academy of Dermatology , American Society for Dermatologic Surgery Disclosure: Nothing to disclose.

Specialty Editor Board Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference Disclosure: Received salary from Medscape for employment. for: Medscape. Wayne Karl Stadelmann, MD Stadelmann Plastic Surgery, PC Chief Editor Gregory Gary Caputy, MD, PhD, FICS Chief Surgeon, Aesthetica Gregory Gary Caputy, MD, PhD, FICS is a member of the following medical societies: American Society for Laser Medicine and Surgery , International College of Surgeons , International College of Surgeons US Section , Pan-Pacific Surgical Association, Wound Healing Society Disclosure: Nothing to disclose. Additional Contributors Shahin Javaheri, MD Chief, Department of Plastic Surgery, Martinez Veterans Affairs Outpatient Clinic; Consulting Staff, Advanced Aesthetic Plastic & Reconstructive Surgery Shahin Javaheri, MD is a member of the following medical societies: American Academy of Otolaryngology-Head and Neck Surgery , American Society of Plastic Surgeons Disclosure: Nothing to disclose.

Acknowledgements The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous authors Don R Revis Jr, MD, Michael Brent Seagle, MD, David J Rowe, MD, MS, Ashley C Campbell, Ali S Totonchi, MD, and Hooman Soltanian, MD, FACS, to the development and writing of this article. Dermis - YouTube Dermis Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. The interactive transcript could not be loaded. Loading... Rating is available when the video has been rented. This feature is not available right now. Please try again later. Published on Oct 25, 2014 The dermis is a layer of skin between the epidermis (with which it makes up the cutis) and subcutaneous tissues, that consists of connective tissue and cushions the body from stress and strain. It is divided into two layers, the superficial area adjacent to the epidermis called the papillary region and a deep thicker area known as the reticular dermis. The dermis is tightly connected to the epidermis through a basement membrane.

Structural components of the dermis are collagen, elastic fibers, and extrafibrillar matrix. It also contains Mechanoreceptors that provide the sense of touch and heat, hair follicles, sweat glands, sebaceous glands, apocrine glands, lymphatic vessels and blood vessels. Those blood vessels provide nourishment and waste removal for both dermal and epidermal cells. This video is targeted to blind users. Attribution: Article text available under CC-BY-SA Creative Commons image source in video Category The dermis AN ORGAN REVEALED The dermis Made up of 80% water, elastin fibres and collagen floating in a glycoprotein gel, the dermis is the tissue supporting the skin. In contrast with the epidermis, it is vascularised, enabling it to not only provide energy and nutrition to the epidermis but also to play a primordial role in thermoregulation and in healing . Zoom Collagen and elastin fibers in Scanning electron microscopy The dermis is 10 to 40 times thicker than the epidermis. At the junction with the epidermis, its surface bristles with fibrous, vascular and nervous projections - the dermal papillae.

The fibroblasts are the main cells in the dermis. They are essentially located in the dermal papillae close to the epidermis, and found only in very low numbers in the deep layers of the dermis known as the reticular dermis. They are specialised in producing two types of protein fibres, collagen and elastin fibres constituent of the extra-cellular matrix. Collagen fibres, 70% of the proteins in the dermis, gives dermis its resistance to strain and traction, while elastin supply its elastic properties. The reticular dermis accounts for the greater part of the dermis. On this level, the elastin and collagen fibres are multidirectional, whereas in the dermal papillae the elastin fibres are mainly oriented perpendicular to the skin surface. Zoom Scanning electron microscopy of Blood capillary. Red blood cell inside the capillary. A large number of blood vessels, small in diameter organised into plexus , cover the entire upper level of the dermis, but do not penetrate the epidermis. In particular, they are concentrated beneath the dermal papillae and even deeper, almost in contact with the hypodermis.

They bring nutrients to the epidermis and contribute to cutaneous thermoregulation . Parts of the skin, lower dermis, dermis, epidermis, sebaceous glands, hair, Beauty, natural cosmetics, herbal formulas for skincare, integrative therapies, mind-body therapies Parts of the Skin Our skin is a complex engineered covering. The skin has a slightly acidic coating of oil at the surface. This coating protects the skin against some bacteria. Below the surface is a complex of sweat and oil glands, hair follicles, blood vessels, nerves, and muscle tissue. These are held together by a tough connective tissue called collagen. Collagen is very important in determining the health of the skin. The relative health of the collagen determines the contour of the skin, how wrinkled and lined it is. Healthy collagen is often called soluble collagen, because it can absorb and hold moisture. Below the collagen is a layer of fat and muscle, which provides some contour and acts as a cushion and as insulation. The skin has three layers. The inner most layer is known as the lower dermis, the middle layer is called the dermis, and the outer layer is known as the epidermis.

Lower Dermis The various glands such as the oil and sweat glands originate in the lower dermis. From here, they rise to the surface of the skin to eliminate waste matter. Lower dermis also acts as a cushion for the rest of the skin. It contains the finely distributed muscles of the skin which regulate body temperature. Dermis The dermis is the layer that lies underneath the epidermis, and it is composed entirely of living cells. It consists of bundles of tough fibers which give your skin its elasticity, firmness and strength. There are also blood vessels, which feed vital nutrients to these areas. The most important function of dermis is respiration. The countless tiny blood vessels, or capillaries end here in finely-drawn networks, from where they feed the outer skin layer. Dermis also determines the tone of the skin. Epidermis This is the top layer of skin and the one you can actually see. It protects your body from invasion and infection and helps to seal in moisture. It's built up of several layers of living cells which are then topped by sheets of dead cells. It's constantly growing, with new cells being produced at its base.

They quickly die, and are pushed up to the surface by the arrival of new ones, These dead cells eventually flake away, which means that every new layer of skin is another chance to have a soft, glowing complexion. The lower levels of living cells are fed by the blood supply from underneath, whereas the upper dead cells only need water to ensure they're kept plump and smooth. The epidermis is responsible for your coloring, as it holds the skin's pigment. It ranges in thickness from l/20-th of an inch on the palms and soles, to 1/200-th of an inch on the face. The skin contains the following specialized organs: Sebaceous glands are tiny organs which usually open into hair follicles on the surface of your skin. They produce an oily secretion, called sebum, which is your skin's natural lubricant. The sebaceous glands are most concentrated on the scalp and face - particularly around the nose, cheeks, chin and forehead, which is why these are usually the most oily areas of your skin. Sweat glands are all over your body. There are millions of them and their main function is to regulate your body temperature.

When sweat evaporates on the skin's surface, the temperature of your skin drops. Hairs grow from the hair follicles. They can help keep your body warm by trapping air underneath them. There are no hairs on the soles of your feet and palms of your hands. Next Topic: 1stholistic.com and Holisticonline.com are developed and maintained by ICBS Send mail to: info@holisticonline.com with comments about this web site. The Skin (Human Anatomy): Picture, Definition, Function, and Skin Conditions The epidermis, the outermost layer of skin, provides a waterproof barrier and creates our skin tone. The dermis, beneath the epidermis, contains tough connective tissue, hair follicles, and sweat glands. The deeper subcutaneous tissue (hypodermis) is made of fat and connective tissue. The skin’s color is created by special cells called melanocytes, which produce the pigment melanin. Melanocytes are located in the epidermis. Skin Conditions Rash : Nearly any change in the skin’s appearance can be called a rash. Most rashes are from simple skin irritation; others result from medical conditions. Dermatitis : A general term for inflammation of the skin.

Atopic dermatitis (a type of eczema) is the most common form. Eczema : Skin inflammation (dermatitis) causing an itchy rash. Most often, it’s due to an overactive immune system. Psoriasis : An autoimmune condition that can cause a variety of skin rashes. Silver, scaly plaques on the skin are the most common form. Dandruff : A scaly condition of the scalp may be caused by seborrheic dermatitis, psoriasis, or eczema. Acne : The most common skin condition, acne affects over 85% of people at some time in life. Cellulitis : Inflammation of the dermis and subcutaneous tissues, usually due to an infection. A red, warm, often painful skin rash generally results. Skin abscess (boil or furuncle): A localized skin infection creates a collection of pus under the skin. Some abscesses must be opened and drained by a doctor in order to be cured. Rosacea : A chronic skin condition causing a red rash on the face. Rosacea may look like acne, and is poorly understood.

Warts : A virus infects the skin and causes the skin to grow excessively, creating a wart. Warts may be treated at home with chemicals, duct tape, or freezing, or removed by a physician. Melanoma : The most dangerous type of skin cancer, melanoma results from sun damage and other causes. A skin biopsy can identify melanoma. Basal cell carcinoma : The most common type of skin cancer. Basal cell carcinoma is less dangerous than melanoma because it grows and spreads more slowly. Seborrheic keratosis : A benign, often itchy growth that appears like a “stuck-on” wart. Seborrheic keratoses may be removed by a physician, if bothersome. Actinic keratosis : A crusty or scaly bump that forms on sun-exposed skin. Actinic keratoses can sometimes progress to cancer. Squamous cell carcinoma : A common form of skin cancer, squamous cell carcinoma may begin as an ulcer that won’t heal, or an abnormal growth. It usually develops in sun-exposed areas. Herpes : The herpes viruses HSV-1 and HSV-2 can cause periodic blisters or skin irritation around the lips or the genitals.

Hives : Raised, red, itchy patches on the skin that arise suddenly. Hives usually result from an allergic reaction. Tinea versicolor : A benign fungal skin infection creates pale areas of low pigmentation on the skin. Viral exantham : Many viral infections can cause a red rash affecting large areas of the skin. This is especially common in children. Shingles (herpes zoster): Caused by the chickenpox virus, shingles is a painful rash on one side of the body. A new adult vaccine can prevent shingles in most people. Scabies : Tiny mites that burrow into the skin cause scabies. An intensely itchy rash in the webs of fingers, wrists, elbows, and buttocks is typical of scabies. Ringworm : A fungal skin infection (also called tinea). The characteristic rings it creates are not due to worms. Continued Skin Tests Skin biopsy : A piece of skin is removed and examined under a microscope to identify a skin condition. Skin testing (allergy testing): Extracts of common substances (such as pollen) are applied to the skin, and any allergic reactions are observed.

Tuberculosis skin test (purified protein derivative or PPD): Proteins from the tuberculosis (TB) bacteria are injected under the skin. In someone who’s had TB, the skin becomes firm. Skin Treatments Corticosteroids (steroids): Medicines that reduce immune system activity may improve dermatitis. Topical steroids are most often used. Antibiotics : Medicines that can kill the bacteria causing cellulitis and other skin infections. Antiviral drugs : Medicines can suppress the activity of the herpes virus, reducing symptoms. Antifungal drugs : Topical creams can cure most fungal skin infections. Occasionally, oral medicines may be needed. Antihistamines : Oral or topical medicines can block histamine, a substance that causes itching. Skin surgery : Most skin cancers must be removed by surgery. Immune modulators : Various drugs can modify the activity of the immune system, improving psoriasis or other forms of dermatitis. Skin moisturizers (emollients): Dry skin is more likely to become irritated and itchy. Moisturizers can reduce symptoms of many skin conditions.

WebMD Image Collection Reviewed by Varnada Karriem-Norwood, MD on November 16, 2014 Sources Chapter 4: The skin, hair and nails Chapter 4: The skin, hair and nails Layers of skin Common integument refers to skin and subcutaneous tissue, hair, nails, and breast. The last-named is described with the upper limb. The skin (cutis) provides a waterproof and protective covering for the body, contains sensory nerve endings, and aids in the regulation of temperature. The skin is important, not only in general medical diagnosis and surgery, but also as the seat of many diseases of its own. The study of these is called dermatology (Gk derma, skin). The area of the body surface is about 2 sq m. The temperature of the skin in general is normally about 32 to 36 degrees C. (90 to 96 degrees F.). The skin (fig. 4-1 ) varies in thickness from about 0.5 to 3 mm. It is thicker on the dorsal and extensor than on the ventral and flexor aspects of the body. It is thinner in infancy and in old age.

The stretching of the abdominal skin during pregnancy may result in red streaks (striae gravidarum) that remain as permanent white lines (lineae albicantes). The skin consists of two quite different layers: (1) the epidermis, a superficiallayer of stratified epithelium that develops from ectoderm, and (2) the dermis, or corium, an underlying layer of connective tissue that is largely mesodermal in origin. The dermis makes up the bulk of the skin. Corium (dermis) The corium, or dermis, contains down growths from the epidermis, such as hair follicles and glands. It presents a superficial papillary layer of loose collagenous and elastic fibers, together with fibroblasts, mast cells, and macrophages. Elevations (papillae) project toward the epidermis. The thicker, deep reticular layer of the dermis consists of dense, coarse bundles of collagenous fibers. Some of the fibers enter the subcutaneous tissue, where they form bundles between lobules of fat. Smooth muscle is found in some regions (areola and nipple, scrotum and penis, and perineum).

In some areas, muscle fibers of skeletal type (e.g., platysma) may be inserted into the skin. In tattooing, foreign particles, such as carbon, are introduced into the dermis. The skin lies on the subcutaneous tissue ("superficial fascia"), a layer of fatty areolar tissue that overlies the more densely fibrous fascia. It should be remembered that fat is liquid, or nearly so, at body temperature. The subcutaneous tissue serves as a depot for fat storage and aids in preventing loss of heat. When a pinch of skin is picked up, subcutaneous tissue is included. A hypodermic injection is one given into the subcutaneous tissue. Epidermis The skin is covered by a film of emulsified material produced by glands and by cornification. The epidermis is an avascular layer of stratified squamous epithelium that is thickest on the palms and soles. The epidermis, where it is thick, presents five layers, as listed in table 4-1 . In the outer layers, which may conveniently be grouped as the horny zone, the cells become converted into soft-keratin flakes that are worn away from the surface continuously.

The stratum corneum is a tough, resilient, semitransparent cellular mem brane that acts as a barrier to water transfer. Under normal conditions, mitotic figures are practically confined to the deepest layer, the stratum basale, which is, therefore, the normal germinative layer of the epidermis. The various layers show the stages through which the basal cells pass before their keratinization and shedding. The cells of the epidermis are replaced approximately once per month. Keratin is a protein that is present throughout the epidermis, perhaps in a modified form. It is readily hydrated-hence the swelling of skin on immersion in water-and dryness of the skin is due chiefly to a lack of water. Human epidermis displays a rhythmic mitotic cycle. Mitosis is more active at night, and it is stimulated by a loss of the superficial, or horny, zone. A part, or the whole thickness, of the epidermis may be raised up in the form of blisters by plasma when the skin is damaged (e.g., by a second-degree burn), and prolonged pressure and friction result in callosities and corns.

Several pigments, including melanin, melanoid, carotene, reduced hemoglobin, and oxyhemoglobin, are found in the skin. Melanin, which is situated chiefly in the stratum basale of the epidermis, protects the organism from ultraviolet light. When an area of epidermis, together with the superficial part of the underlying dermis, is destroyed, new epidermis is formed from hair follicles, and also from sudoriferous and sebaceous glands, where these are present. If the injury involves the whole thickness of the dermis (e.g., in a deep burn), however, epithelization can take place only by a growing over of the surrounding edge of the epidermis or alternatively by the use of an autograft. Free skin grafts of the epidermis and a part or all of the thickness of the dermis can be applied, and vascularization takes place through connections between the subcutaneous vessels and those in the graft. A defect of the skin that extends into the dermis is termed an ulcer. Lines of thickened epidermis known as papillary ridges form a characteristic pattern on the palmar aspect of the hand and the plantar aspect of the foot.

They are concerned with tactile sensation. They contain the openings of the sweat glands and overlie grooves in the dermis; these grooves are situated typically between rows of double ridges known as dermal ridges (fig. 4-1 ). The papillary ridges appear in fetal life in a pattern that remains permanently. They are especially well developed in the pads of the digits, and finger prints in adults and foot prints in infants are used as a means of identification of an individual. Specialized structures of skin Sweat (sudoriferous glands) The sweat, or sudoriferous, glands regulate body temperature, because perspiration withdraws heat from the body by the vaporization of water. The sweat glands develop in the fetus as epidermal downgrowths that become canalized. They are simple tubular glands, each having a coiled secretory unit in the dermis or in the subcutaneous tissue and a long, winding duct that extends through the epidermis and opens by a pore on the surface of the skin (fig. 4-1 ). Sweat glands are particularly numerous in the palms and the soles, where they open on the summits of the papillary ridges.

The chief stimuli to sweating are heat and emotion. Emotional perspiration occurs characteristically on the forehead, axillae, palms, and soles. Large sweat glands in certain locations, such as the axilla, areola, external acoustic meatus, and eyelid, develop from hair follicles and differ from the more common (eccrine) glands in being apocrine; that is to say, portions of the secreting cells disintegrate in the process of secretion. The perspiration from the apocrine glands is rich in organic material that is susceptible to bacterial action, resulting in an odor. Water passes through the epidermis also by diffusion. This is termed insensible perspiration because it cannot be seen or felt. Hairs Hairs (or pili; pilus in the singular) are characteristic of mammals. The functions of hair include protection, regulation of body temperature, and facilitation of evaporation of perspiration; hairs also act as sense organs. Hairs develop in the fetus as epidermal downgrowths that invade the underlying dermis. Each downgrowth terminates in an expanded end that becomes invaginated by a mesodermal papilla.

The central cells of the downgrowth become keratinized to form a hair, which then grows outward to reach the surface. The hairs first developed constitute the lanugo, or down, which is shed shortly before birth. The fine hairs that develop later constitute the vellus. Although hairs on many portions of the human body are inconspicuous, their actual number per unit area is large. In a few places (such as the palms and the soles and the dorsal aspect of the distal phalanges) the skin is glabrous, that is, devoid of hair. The shaft of a hair consists of a cuticle and a cortex of hard-keratin surrounding, in many hairs, a soft-keratin medulla (fig. 4-2 ). Pigmented hairs contain melanin in the cortex and medulla, but pigment is absent from the surrounding sheaths. The color of hair depends mainly on the shade and the amount of pigment in the cortex and, to a lesser extent, on air spaces in the hair. In white hairs pig ment is absent from the cortex, and the contained air is responsible for the whiteness; "gray hair" is generally a mixture of white and colored hairs.

The root of a hair is situated in an epidermal tube known as the hair follicle, sunken into either the dermis or the subcutaneous tissue. The follicle is dilated at its base to form the bulb (matrix). In the obtuse angle between the root of a hair and the surface of the skin, a bundle of smooth muscle fibers, known as an arrector pili muscle, is usually found. It extends from the deep part of the hair follicle to the papillary layer of the dermis. On contraction it makes the hair erect. The arrectores pilorum are innervated by sympathetic fibers and contract in response to emotion or cold. This results in an unevenness of the surface called "goose pimples" or "goose skin." Sebaceous glands Sebaceous glands develop from the epidermis in the fetus, usually from the walls of hair follicles. Sebaceous glands are absent from the palms and the soles. They are simple alveolar glands that form lobes in the dermis, generally in the acute angle between an arrector pili and its hair follicle.

The basal cells of the gland proliferate, accumulate fat droplets, and are excreted as sebum through a short, wide duct into the lumen of the hair follicle. Contraction of the arrector pili may perhaps aid in expelling the sebum. Sebum keeps the stratum corneum pliable and, in cold weather, conserves body heat by hindering evaporation. Fat-soluble substances may penetrate the skin through hair follicles and sebaceous glands. Hence ointment vehicles are used when penetration is desired. Medicaments should be rubbed into the skin. Sebaceous glands that are not related to hairs are found in the eyelids as tarsal glands; these are said to be apocrine in type, as are the ceruminous glands of the external acoustic meatus. Seborrhea involves an excessive secretion of sebum; the sebum may collect on the surface as scales known as dandruff. Acne is a chronic inflammatory condition of the sebaceous glands. When the exit from a sebaceous gland becomes plugged, a blackhead (comedo) forms; complete blockage may result in a wen (sebaceous cyst).

At birth an infant is covered with vernix caseosa, a mixture of sebum and desquamated epithelial cells. Nails The nails (or ungues; unguis in the singular) are hardenings of the horny zone of the epidermis. They overlie the dorsal aspect of the distal phalanges (fig. 4-3 ). They protect the sensitive tips of the digits and, in the fingers, serve in scratching. Nails develop in the fetus as epidermal thickenings that undercut the skin to form folds from which the horny substance of the nail grows distally. The horny zone of the nail is composed of hard-keratin and has a distal, exposed part, or body, and a proximal, hidden portion, or root. The root is covered by a distalward prolongation of the stratum corneum of the skin. This narrow fold is composed of soft-keratin and is termed the eponychium. Distal to the eponychium is the "half-moon," or lunula, a part of the horny zone that is opaque to the underlying capillaries.

Deep to the distal or free border of the nail, the horny zone of the fingertip is thickened and is frequently termed the hyponychium. The horny zone of the nail is attached to the underlying nail bed. The matrix, or proximal part of the bed, produces hard-keratin. Further distally, however, the bed may also generate nail substance. Moreover, the most superficiallayer of the nail may be produced by the epithelium immediately dorsal to the root and proximal to the eponychium. The growth of the nail is affected by nutrition, hormones, and disease. Nail growth involves considerable protein synthesis, as a result of which nonspecific changes occur in the nails in response to various local and systemic disturbances. White spots indicate incomplete keratinization. Blood supply and innervation of skin The skin has a profuse blood supply, which is important in temperature regulation. The subcutaneous arteries form a network in the subcutaneous tissue, and from this is derived a subpapillary plexus in the dermis. Capillary loops in the dermal papillae arise from the subpapillary plexus, and from these loops the avascular epidermis is bathed in tissue fluid.

A subpapillary plexus of venules gives the skin its pink color: the vessels become dilated when the skin is heated, and thereby make it look red. Most birthmarks consist of dilated capillaries (hemangioma). The dermis contains a lymphatic plexus that drains into the collecting vessels in the subcutaneous tissue. The cutaneous lymphatics can be shown in vivo by injecting vital dyes, and every intradermal injection is an intralymphatic one. The skin has a rich sensory innervation (fig. 4-4 ). The cutaneous nerves pierce the fascia and ramify in the subcutaneous tissue to form plexuses both there and in the dermis. Finer axonal ramifications may run between the deeper cells of the epidermis. The cutaneous nerves supply both the skin and the subcutaneous tissue. The area of distribution of a given nerve, however, varies, and considerable overlapping of adjacent nerve territories takes place.

Nerves supplying the skin may form several different types of nerve endings, and these endings have been related in a general way to the basic types of sensations that can be appreciated in the skin and the subcutaneous tissue, namely, pain, touch, temperature changes, and pressure, or deep touch. Hairy skin contains simple, free endings and plexuses around the hair follicles. Skin without hair, that of the palm, for example, presents the three types of sensory endings that are characteristic of the somatic nervous system: (1) free nerve endings arising from small myelinated fibers, (2) expanded tips, and (3) encapsulated endings. The basic types of sensation, however, can be elicited from both hairy and glabrous skin. Hence correlations between the type of sensation and a specific type of nerve ending are not justified. Lamellated corpuscles are particularly large, encapsulated endings that are found chiefly in the subcutaneous and deeper tissues. Additional reading Jarrett, A. (ed.), The Physiology and Pathophysiology of the Skin. Academic Press, New York, 1973, 1974.

Volume 1 is on the epidermis, volume 2 on nerves and blood vessels, and volume 3 on the dermis. Montagna, W., and Parakkal, P. F., The Structure and Function of Skin, 3rd ed. Academic Press, New York, 1974. A good introduction. Pinkus, H., Die makroskopische Anatomie der Haut, in Normale und pathologische Anatomie der Haut. ed. by O. Gans and G. K. Steigleder, Springer, Berlin, vol. 2, 1964. An excellent account. Questions 4-1 How do the two layers of the skin differ? 4-1 The two layers of the skin differ structurally and developmentally. The epidermis is a stratified epithelium of ectodermal origin. The dermis is a connective tissue largely of mesodermal origin. 4-2 Into which layer is a hypodermic injection given? 4-2 A hypodermic injection is given into the subcutaneous tissue, formerly called" superficial fascia." 4-3 What is normally the germinative layer of the epidermis?

4-3 The deepest layer of the epidermis, stratum basale, is normally its germinative layer. 4-4 What is a second-degree burn? 4-4 In Dupuytren's classification (1832) a second-degree burn affects part of the epidermis, resulting in vesiculation (blisters) in addition to redness (erythema). See figure 4-1 . 4-5 How does water leave the skin? 4-5 Water leaves the skin not only through the glands as perspiration but also by diffusion through the epidermis (insensible perspiration). 4-6 What is an arrector pili and how does it function? 4-6 The arrectores pilorum are bundles of smooth muscle associated with hair follicles. On exposure to cold or under emotion (sympathetic nerves), they elevate the hair in a lever-like manner, and the nearby skin is depressed, whereas the surrounding skin is elevated ("goose skin"). 4-7 What is the function of sebum? 4-7 Sebum (from sebaceous glands) keeps the stratum corneum pliable and conserves body heat by hindering evaporation.

Seborrhea involves an excessive secretion of sebum, which may collect on the surface as scales (dandruff). 4-8 Can the different types of nerve endings in the skin be related to the basic types of sensation (pain, touch, temperature changes, and pressure, or deep touch)? 4-8 Different types of nerve endings of the skin can be related to basic kinds of sensation in only a general way. Correlations between type of sensation and a specific type of nerve ending are not justified. Figure legends Figure 4-1 General view of skin and subcutaneous tissue. A, "Thin" skin from abdomen. B, "Thick" skin from pal m of hand. X, Y, and Z represent the levels of a superficial (Thiersch) graft, a split thickness graft (including one third to one quarter of the dermis), and a full thickness (Wolfe) graft, respectively. The numerals 1 to 6 represent the levels of degrees of burns, according to Dupuytren's classification. Other classifications of burns are also used. Figure 4-2 Diagram of a hair follicle.

The follicle consists of an external root sheath, mainly the basal-cell layer of the epidermis, and an internal root sheath of soft-keratin, which includes a cuticle firmly anchored to that of the shaft of the hair. Figure 4-3 Diagram of a sagittal section of a fingernail. The arrow indicates the junction between the root and body of the nail. Figure 4-4 Diagram of the innervation of the skin. The numerals 1, 2, and 3 indicate the epidermis, dermis, and subcutaneous tissue, respectively. The letters A and C stand for adrenergic and cholinergic nerve fibers, respectively. Jump to:

Question: The dermis and cutis are parts of the human?
Answer: Skin