Keratin | definition of keratin by Medical dictionary Keratin | definition of keratin by Medical dictionary keratin [ker´ah-tin] a scleroprotein that is the principal constituent of epidermis, hair, nails, horny tissues, and the organic matrix of the enamel of the teeth. Its solution is sometimes used in coating pills when the latter are desired to pass through the stomach unchanged. ker·a·tin (ker'ă-tin), Collective name for a group of proteins that form the intermediate filaments in epithelial cells. Keratins have a molecular weight between 40 kD and 68 kD and are separated one from another by electrophoresis and isoelectric focusing; thus separated, they are sequentially numbered from 1-20, and also subdivided into low, intermediate, and high molecular weight proteins. According to their isoelectric mobility they are either acidic or basic. In general, each acidic keratin protein has its basic equivalent with which it is paired to form the intermediate filaments; some keratin proteins, however, occur unpaired. Various epithelial cells contain different keratin proteins, in a tissue-specific manner.

Antibodies to keratin proteins are widely used for histologic typing of tumors, and are especially useful for distinguishing carcinomas from sarcomas, lymphomas, and melanomas. [G. keras (kerat-), horn, + -in] keratin /ker·a·tin/ (ker´ah-tin) any of a family of scleroproteins that are the main constituents of epidermis, hair, nails, and horny tissues. The high-sulfur keratin polypeptides of ectodermally derived structures, e.g., hair and nails, are also called hard k's. keratin (kĕr′ə-tĭn) n. 1. Any of a class of filamentous proteins that are abundant in the cytoskeleton of vertebrate epithelial cells and are the main constituents of the outer layer of skin and tough epidermal structures such as hair, nails, hooves, feathers, and claws. 2. Material composed principally of keratin proteins. ke·rat′i·nous (kə-răt′n-əs) adj.

keratin [ker′ətin] Etymology: Gk, keras, horn a fibrous sulfur-containing protein that is the primary component of the epidermis, hair, nails, enamel of the teeth, and horny tissue of animals. The protein is insoluble in most solvents, including gastric juice. For this reason, it is often used as a coating for pills that must pass through the stomach unchanged to be dissolved in the intestines. ker·a·tin (ker'ă-tin) A scleroprotein or albuminoid present in hair and nails; it contains a relatively large amount of sulfur, is insoluble in gastric juice, and is sometimes used for coating tablets that are intended to be dissolved only in the intestine. [G. keras (kerat-), horn, + -in] keratin A hard protein (scleroprotein) of cylindrical, helical molecular form occurring in horny tissue such as hair and nails and in the outer layers of the skin. Hair and nails consist almost wholly of keratin. Keratins are insoluble and cannot generally be split by PROTEOLYTIC enzymes.

keratin a hard, fibrous, sulphur-containing protein with an alpha-helix structure, found in the epidermis of vertebrates, mainly in the outermost layers of skin. Keratin can have several forms: in scales, feathers, hooves, horns, claws and nails it is hard, while wool and hair are made up of a soft and flexible form. Keratin A tough, nonwater-soluble protein found in the nails, hair, and the outermost layer of skin. Human hair is made up largely of keratin. keratin sulphur-containing, insoluble scleroprotein, forming stratum corneum, nail plate and hair shaft, from enzymic conversion of epidermal cells ker·a·tin (ker'ă-tin) Collective name for a group of proteins that form intermediate filaments in epithelial cells. Keratins have a molecular weight of 40-68 kD and are either acidic or basic. Antibodies to keratin proteins are widely used for histologic typing of tumors and are especially useful for distinguishing carcinomas from sarcomas, lymphomas, and melanomas. [G.

keras (kerat-), horn, + -in] keratin (ker´ətin), n. an insoluble sulfur-containing protein with a high content of the amino acids tyrosine and leucine; the main component of epidermis, hair, nails, keratinized epithelium. It contains a relatively large amount of sulfur, is insoluble in the gastric juices, and is sometimes used for coating enteric pills that are intended to be dissolved only in the intestine. keratin layer, n the outer layer of cells of the epidermis, which contain a tough, fibrous protein (keratin). This layer acts as a protective barrier against outside elements. keratin a scleroprotein which is the principal constituent of epidermis, hair, nails, horny tissues, and the organic matrix of the enamel of the teeth. Its solution is sometimes used in coating pills when the latter are desired to pass through the stomach unchanged. keratin cyst Skin, Hair, and Nails Skin, Hair, and Nails La piel, el cabello y las uñas About Skin, Hair and Nails Skin is our largest organ.

If the skin of a typical 150-pound (68-kilogram) adult male were stretched out flat, it would cover about 2 square yards (1.7 square meters) and weigh about 9 pounds (4 kilograms). Our skin protects the network of muscles, bones, nerves, blood vessels, and everything else inside our bodies. Our eyelids have the thinnest skin, the soles of our feet the thickest. Hair is actually a modified type of skin. Hair grows everywhere on the human body except the palms of the hands, soles of the feet, and lips. Hair grows more quickly in summer than winter, and more slowly at night than during the day. Like hair, nails are a type of modified skin. Nails protect the sensitive tips of fingers and toes. Human nails aren't necessary for living, but they do provide support for the tips of the fingers and toes, protect them from injury, and aid in picking up small objects. Without them, we'd have a hard time scratching an itch or untying a knot. Nails can be an indicator of a person's general health, and illness often affects their growth. continue Skin Basics Skin is essential in many ways.

It forms a barrier that prevents harmful substances and microorganisms from entering the body. It protects body tissues against injury. It also controls the loss of life-sustaining fluids like blood and water, helps regulate body temperature through perspiration (sweating), and protects from the sun's damaging ultraviolet rays. Without the nerve cells in skin, people couldn't feel warmth, cold, or other sensations. For instance, goosebumps form when the erector pili muscles contract to make hairs on the skin stand up straight when someone is cold, excited, or frightened — the blood vessels keep the body from losing heat by narrowing as much as possible and keeping the warm blood away from the skin's surface, offering insulation and protection. Every square inch of skin contains thousands of cells and hundreds of sweat glands, oil glands, nerve endings, and blood vessels. Skin is made up of three layers: the epidermis, dermis, and the subcutaneous tissue. The upper layer of our skin, the epidermis, is the tough, protective outer layer. It's about as thick as a sheet of paper over most parts of the body. The epidermis has four layers of cells that are constantly flaking off and being renewed.

In these four layers are three special types of cells: Melanocytes produce melanin, the pigment that gives skin its color. All people have roughly the same number of melanocytes; the more melanin that is produced, the darker the skin. Exposure to sunlight increases the production of melanin, which is why people get suntanned or freckled. Keratinocytes produce keratin, a type of protein that is a basic component of hair, skin, nails, and helps create an intact barrier. Langerhans cells help protect the body against infection. Because the cells in the epidermis are completely replaced about every 28 days, cuts and scrapes heal quickly. Below the epidermis is the next layer of our skin, the dermis, which is made up of blood vessels, nerve endings, and connective tissue. The dermis nourishes the epidermis. Two types of fibers in the dermis — collagen and elastin — help the skin stretch when we bend and reposition itself when we straighten up. Collagen is strong and hard to stretch, and elastin, as its name suggests, is elastic.

In older people, some of the elastin-containing fibers degenerate, which is one reason why the skin looks wrinkled. The dermis also contains a person's sebaceous glands. These glands, which surround and empty into hair follicles and pores, produce the oil sebum that lubricates the skin and hair. Sebaceous glands are found mostly in the skin on the face, upper back, shoulders, and chest. Most of the time, the sebaceous glands make the right amount of sebum. As a person's body begins to mature and develop during the teenage years, though, hormones stimulate the sebaceous glands to make more sebum. When pores become clogged by too much sebum and too many dead skin cells, this contributes to acne. Later in life, these glands produce less sebum, which contributes to dry skin as people age. The bottom layer of our skin, the subcutaneous tissue, is made up of connective tissue, sweat glands, blood vessels, and cells that store fat. This layer helps protect the body from blows and other injuries and helps it hold in body heat.

There are two types of sweat glands: The eccrine glands are found everywhere, although they're mostly in the forehead, palms, and soles of the feet. By producing sweat, these glands help regulate body temperature, and waste products are excreted through them. The apocrine glands develop at puberty and are concentrated in the armpits and pubic region. The sweat from the apocrine glands is thicker than that produced by the eccrine glands. Although this sweat doesn't smell, when it mixes with bacteria on the skin's surface, it can cause body odor. A normal, healthy adult secretes about 1 pint (about half a liter) of sweat daily, but this may be increased by physical activity, fever, or a hot environment. previous continue Hair Basics The hair on our heads isn't just there for looks. It keeps us warm by preserving heat. The hair in the nose, ears, and around the eyes protects these sensitive areas from dust and other small particles. Eyebrows and eyelashes protect eyes by decreasing the amount of light and particles that go into them. The fine hair that covers the body provides warmth and protects the skin. Hair also cushions the body against injury.

Human hair consists of the hair shaft, which projects from the skin's surface, and the root, a soft thickened bulb at the base of the hair embedded in the skin. The root ends in the hair bulb, which sits in a sac-like pit in the skin called the follicle, from which the hair grows. At the bottom of the follicle is the papilla, where hair growth actually takes place. The papilla contains an artery that nourishes the root of the hair. As cells multiply and produce keratin to harden the structure, they're pushed up the follicle and through the skin's surface as a shaft of hair. Each hair has three layers: the medulla at the center, which is soft; the cortex, which surrounds the medulla and is the main part of the hair; and the cuticle, the hard outer layer that protects the shaft. Hair grows by forming new cells at the base of the root. These cells multiply to form a rod of tissue in the skin. The rods of cells move upward through the skin as new cells form beneath them. As they move up, they're cut off from their supply of nourishment and start to form a hard protein called keratin in a process called keratinization.

As this process occurs, the hair cells die. The dead cells and keratin form the shaft of the hair. Each hair grows about ¼ inch (about 6 millimeters) every month and keeps on growing for up to 6 years. The hair then falls out and another grows in its place. The length of a person's hair depends on the length of the growing phase of the follicle. Follicles are active for 2 to 6 years; they rest for about 3 months after that. A person becomes bald if the scalp follicles become inactive and no longer produce new hair. Thick hair grows out of large follicles; narrow follicles produce thin hair. The color of a person's hair is determined by the amount and distribution of melanin in the cortex of each hair (the same melanin that's found in the epidermis). Hair also contains a yellow-red pigment; people who have blonde or red hair have only a small amount of melanin in their hair. Hair becomes gray when people age because pigment no longer forms. Nail Basics Nails grow out of deep folds in the skin of the fingers and toes.

As epidermal cells below the nail root move up to the surface of the skin, they increase in number, and those closest to the nail root become flattened and pressed tightly together. Each cell is transformed into a thin plate; these plates are piled in layers to form the nail. As with hair, nails are formed by keratinization. When the nail cells accumulate, the nail is pushed forward. The skin below the nail is called the matrix. The larger part of the nail, the nail plate, looks pink because of the network of tiny blood vessels in the underlying dermis. The whitish crescent-shaped area at the base of the nail is called the lunula. Fingernails grow about three or four times as quickly as toenails. Like hair, nails grow more rapidly in summer than in winter. If a nail is torn off, it will regrow if the matrix isn't severely injured. White spots on the nail are sometimes due to temporary changes in growth rate. Things That Can Affect Skin, Hair, and Nails Dermatitis The term dermatitis refers to any inflammation (swelling, itching, and redness) possibly associated with the skin. There are many types of dermatitis, including: Atopic dermatitis (eczema).

It's a common, hereditary dermatitis that causes an itchy rash primarily on the face, trunk, arms, and legs. It commonly develops in infancy, but can also appear in early childhood. It may be associated with allergic diseases such as asthma and seasonal, environmental, and food allergies. Contact dermatitis. This occurs when the skin comes into contact with an irritating substance or one that the person is allergic or sensitive to. The best-known cause of contact dermatitis is poison ivy, but there are many others, including chemicals found in laundry detergent, cosmetics, and perfumes, and metals like nickel plating on jewelry, belt buckles, and the back of a snap. Seborrheic dermatitis. This oily rash, which appears on the scalp, face, chest, and back, is related to an overproduction of sebum from the sebaceous glands. This condition is common in infants and adolescents. Bacterial Skin Infections Impetigo . Impetigo is a bacterial infection that results in a honey-colored, crusty rash, often on the face near the mouth and nose. Cellulitis .

Cellulitis is an infection of the skin and subcutaneous tissue that typically occurs when bacteria are introduced through a puncture, bite, or other break in the skin. The area with cellulitis is usually warm, tender, and has some redness. Streptococcal and staphylococcal infections. These two kinds of bacteria are the main causes of cellulitis and impetigo. Certain types of these bacteria are also responsible for distinctive rashes on the skin, including the rashes associated with scarlet fever and toxic shock syndrome . Fungal Infections of the Skin and Nails Candidal dermatitis. A warm, moist environment, such as that found in the folds of the skin in the diaper area of infants, is perfect for growth of the yeast Candida. Yeast infections of the skin in older children, teens, and adults are less common. Tinea infection (ringworm) . Ringworm, which isn't a worm at all, is a fungus infection that can affect the skin, nails, or scalp. Fungi called dermatophytes can infect the skin and related tissues of the body.

The medical name for ringworm of the scalp is tinea capitis; ringworm of the body is called tinea corporis; and ringworm of the nails is called tinea unguium. With tinea corporis, the fungi can cause scaly, ring-like lesions anywhere on the body. Tinea pedis (athlete's foot). This infection of the feet is caused by the same types of fungi that cause ringworm. Athlete's foot is commonly found in adolescents and is more likely to occur during warm weather. Other Skin Problems Parasitic infestations. Parasites (usually tiny insects or worms) can feed on or burrow into the skin, often resulting in an itchy rash. Scabies and lice are examples of parasitic infestations. Both are contagious and can be easily caught from other people. Viral infections. Many viruses cause characteristic rashes on the skin, including varicella, the virus that causes chickenpox and shingles; herpes simplex, which causes cold sores; human papillomavirus, the virus that causes warts ; and a host of others. Acne (acne vulgaris). Acne is most common in teens.

Some degree of acne is seen in 85% of adolescents, and nearly all teens have the occasional pimple, blackhead, or whitehead. Skin cancer. Skin cancer is rare in children and teens, but good sun protection habits established during these years can help prevent skin cancers such as melanoma (a serious form of skin cancer that can spread to other parts of the body) later in life, especially among fair-skinned people who sunburn easily. Besides these diseases and conditions, the skin can be injured in a number of ways. Minor scrapes, cuts, and bruises heal quickly on their own, but other injuries — severe cuts and burns, for example — require medical treatment. Disorders of the Scalp and Hair Tinea capitis, a type of ringworm, is a fungal infection that forms a scaly, ring-like lesion in the scalp. It's contagious and common among school-age children. Alopecia is an area of hair loss. Ringworm is a common cause of temporary alopecia in children. Alopecia can also be caused by tight braiding that pulls on the hair roots (called tension alopecia).

Alopecia areata (when hair falls out in round or oval patches on the scalp) is a less common condition that can affect children and teens. 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: Keratin 101: What is Keratin Really? | Keratin Questions Answered You are here: Home » Hair Care » Keratin 101: What is Keratin Really? Keratin 101: What is Keratin Really? Remember those days back in biology class? No? Well don’t worry – keratin is not as complicated as you may think. Basically, keratin is a family of proteins that are among the most important and versatile compounds ever produced in nature.

Think of your hair, nails and skin as solid structures – like buildings, armor and carbon fiber – they’re all built for toughness and protection using keratin as the main component. However, in the human body, unlike the industrial world of mechanics and machines, keratin can also help injured cells to heal and grow. Now imagine having a building that could repair itself whenever it became damaged. It’s just a simple way of appreciating how important and amazing keratin really is. Ever wondered what makes your skin waterproof? Yes, you guessed it right…keratin. You may have even seen keratin without knowing it was there in the first place. Rubbing and adding pressure to your skin can cause the outer layer to thicken, forming a protective callus. The thick bit of skin at the edge of a blister and hard skin on the fingertips of musicians who play stringed instruments are all keratinized skin cells. In fact, they are constantly shed and replaced, even by microscopic pressure and rubbing. The next time you see the guy in the elevator with dandruff on his collar and shoulders, don’t be grossed out…instead marvel at the fact that the white stuff is actually keratinized skin cells!

Especially when you consider that your hair is 95% keratin. This means that naturally occurring keratin needs to be incorporated into hair care products in order for them to be effective. We’ll discuss the wonders of Keratin in more detail in the next blog entry. Be Sociable, Share! 49 Responses to Keratin 101: What is Keratin Really? Samantha If the body stopped producing keratin, what would be the effect on the hair? Keratin Questions Structure and Function of the Skin - Skin Disorders - Merck Manuals Consumer Version Structure and Function of the Skin Structure and Function of the Skin By Robert J. MacNeal, MD, Maine Medical Center The skin has three layers: Epidermis Fat layer (also called the subcutaneous layer) Each layer performs specific tasks. Getting Under the Skin The skin has three layers. Beneath the surface of the skin are nerves, nerve endings, glands, hair follicles, and blood vessels. Epidermis The epidermis is the relatively thin, tough, outer layer of the skin. Most of the cells in the epidermis are keratinocytes. They originate from cells in the deepest layer of the epidermis called the basal layer.

New keratinocytes slowly migrate up toward the surface of the epidermis. Once the keratinocytes reach the skin surface, they are gradually shed and are replaced by newer cells pushed up from below. The outermost portion of the epidermis, known as the stratum corneum, is relatively waterproof and, when undamaged, prevents most bacteria, viruses, and other foreign substances from entering the body. The epidermis (along with other layers of the skin) also protects the internal organs, muscles, nerves, and blood vessels against trauma. In certain areas of the body that require greater protection (such as the palms of the hands and the soles of the feet), the outer keratin layer of the epidermis (stratum corneum) is much thicker. Scattered throughout the basal layer of the epidermis are cells called melanocytes, which produce the pigment melanin, one of the main contributors to skin color. Melanin's primary function, however, is to filter out ultraviolet radiation from sunlight (see Overview of Sunlight and Skin Damage ), which damages DNA, resulting in numerous harmful effects, including skin cancer.

The epidermis also contains Langerhans cells, which are part of the skin's immune system. Although these cells help detect foreign substances and defend the body against infection, they also play a role in the development of skin allergies. Dermis The dermis, the skin's next layer, is a thick layer of fibrous and elastic tissue (made mostly of collagen, elastin, and fibrillin) that gives the skin its flexibility and strength. The dermis contains nerve endings, sweat glands and oil (sebaceous) glands, hair follicles, and blood vessels. The nerve endings sense pain, touch, pressure, and temperature. Some areas of the skin contain more nerve endings than others. For example, the fingertips and toes contain many nerves and are extremely sensitive to touch. The sweat glands produce sweat in response to heat and stress. Sweat is composed of water, salt, and other chemicals. As sweat evaporates off the skin, it helps cool the body. Specialized sweat glands in the armpits and the genital region (apocrine sweat glands) secrete a thick, oily sweat that produces a characteristic body odor when the sweat is digested by the skin bacteria in those areas.

The sebaceous glands secrete sebum into hair follicles. Sebum is an oil, that keeps the skin moist and soft and acts as a barrier against foreign substances. The hair follicles produce the various types of hair found throughout the body. Hair not only contributes to a person's appearance but has a number of important physical roles, including regulating body temperature, providing protection from injury, and enhancing sensation. A portion of the follicle also contains stem cells capable of regrowing damaged epidermis. The blood vessels of the dermis provide nutrients to the skin and help regulate body temperature. Heat makes the blood vessels enlarge (dilate), allowing large amounts of blood to circulate near the skin surface, where the heat can be released. Cold makes the blood vessels narrow (constrict), retaining the body's heat. Over different parts of the body, the number of nerve endings, sweat glands and sebaceous glands, hair follicles, and blood vessels varies. The top of the head, for example, has many hair follicles, whereas the soles of the feet have none. Fat layer Below the dermis lies a layer of fat that helps insulate the body from heat and cold, provides protective padding, and serves as an energy storage area.

The fat is contained in living cells, called fat cells, held together by fibrous tissue. The fat layer varies in thickness, from a fraction of an inch on the eyelids to several inches on the abdomen and buttocks in some people. Resources In This Article Keratins | definition of Keratins by Medical dictionary Keratins | definition of Keratins by Medical dictionary Related to Keratins: actin , hard keratin keratin [ker´ah-tin] a scleroprotein that is the principal constituent of epidermis, hair, nails, horny tissues, and the organic matrix of the enamel of the teeth. Its solution is sometimes used in coating pills when the latter are desired to pass through the stomach unchanged. ker·a·tin (ker'ă-tin), Collective name for a group of proteins that form the intermediate filaments in epithelial cells. Keratins have a molecular weight between 40 kD and 68 kD and are separated one from another by electrophoresis and isoelectric focusing; thus separated, they are sequentially numbered from 1-20, and also subdivided into low, intermediate, and high molecular weight proteins.

According to their isoelectric mobility they are either acidic or basic. In general, each acidic keratin protein has its basic equivalent with which it is paired to form the intermediate filaments; some keratin proteins, however, occur unpaired. Various epithelial cells contain different keratin proteins, in a tissue-specific manner. Antibodies to keratin proteins are widely used for histologic typing of tumors, and are especially useful for distinguishing carcinomas from sarcomas, lymphomas, and melanomas. [G. keras (kerat-), horn, + -in] keratin /ker·a·tin/ (ker´ah-tin) any of a family of scleroproteins that are the main constituents of epidermis, hair, nails, and horny tissues. The high-sulfur keratin polypeptides of ectodermally derived structures, e.g., hair and nails, are also called hard k's. keratin (kĕr′ə-tĭn) n. 1.

Any of a class of filamentous proteins that are abundant in the cytoskeleton of vertebrate epithelial cells and are the main constituents of the outer layer of skin and tough epidermal structures such as hair, nails, hooves, feathers, and claws. 2. Material composed principally of keratin proteins. ke·rat′i·nous (kə-răt′n-əs) adj. keratin [ker′ətin] Etymology: Gk, keras, horn a fibrous sulfur-containing protein that is the primary component of the epidermis, hair, nails, enamel of the teeth, and horny tissue of animals. The protein is insoluble in most solvents, including gastric juice. For this reason, it is often used as a coating for pills that must pass through the stomach unchanged to be dissolved in the intestines. ker·a·tin (ker'ă-tin) A scleroprotein or albuminoid present in hair and nails; it contains a relatively large amount of sulfur, is insoluble in gastric juice, and is sometimes used for coating tablets that are intended to be dissolved only in the intestine. [G.

keras (kerat-), horn, + -in] keratin A hard protein (scleroprotein) of cylindrical, helical molecular form occurring in horny tissue such as hair and nails and in the outer layers of the skin. Hair and nails consist almost wholly of keratin. Keratins are insoluble and cannot generally be split by PROTEOLYTIC enzymes. keratin a hard, fibrous, sulphur-containing protein with an alpha-helix structure, found in the epidermis of vertebrates, mainly in the outermost layers of skin. Keratin can have several forms: in scales, feathers, hooves, horns, claws and nails it is hard, while wool and hair are made up of a soft and flexible form. Keratin A tough, nonwater-soluble protein found in the nails, hair, and the outermost layer of skin. Human hair is made up largely of keratin.

keratin sulphur-containing, insoluble scleroprotein, forming stratum corneum, nail plate and hair shaft, from enzymic conversion of epidermal cells ker·a·tin (ker'ă-tin) Collective name for a group of proteins that form intermediate filaments in epithelial cells. Keratins have a molecular weight of 40-68 kD and are either acidic or basic. Antibodies to keratin proteins are widely used for histologic typing of tumors and are especially useful for distinguishing carcinomas from sarcomas, lymphomas, and melanomas. [G. keras (kerat-), horn, + -in] keratin (ker´ətin), n. an insoluble sulfur-containing protein with a high content of the amino acids tyrosine and leucine; the main component of epidermis, hair, nails, keratinized epithelium. It contains a relatively large amount of sulfur, is insoluble in the gastric juices, and is sometimes used for coating enteric pills that are intended to be dissolved only in the intestine. keratin layer, n the outer layer of cells of the epidermis, which contain a tough, fibrous protein (keratin).

This layer acts as a protective barrier against outside elements. keratin a scleroprotein which is the principal constituent of epidermis, hair, nails, horny tissues, and the organic matrix of the enamel of the teeth. Its solution is sometimes used in coating pills when the latter are desired to pass through the stomach unchanged. keratin cyst

Question: In humans, what is the name of the fibrous protein found in the outer layer of the skin and is a major constituent of hair and nails?
Answer: Keratin