4.3: Accessory structures of the skin (2023)

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    At the end of the section you can:

    • Identify the accessory structures of the skin.
    • Describe the structure and function of hair and nails.
    • Describe the structure and function of the sweat glands and the sebaceous glands.

    Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. These structures are embryologically derived from the epidermis and can extend through the dermis to the hypodermis.

    They are

    They are It is a keratin filament that grows from the epidermis. It consists mainly of cornified dead cells. The hair strands arise from an epidermal penetration of the dermis known ashair bellows. Hehair shaftit is the part of the hair that is not anchored to the follicle, and much of it is exposed on the surface of the skin. The rest of the hair that is anchored in the follicle lies below the skin's surface and is known as thehair root. The hair root ends deep in the dermis at thehair wiggle, and contains a layer of mitotically active basal cells calledhair matrix. The hair bulb surrounds thehis papilla, which consists of connective tissue and contains blood capillaries and nerve endings from the dermis (Figure \(\PageIndex{1}\)).

    4.3: Accessory structures of the skin (2)

    Just as the basal layer of the epidermis forms the epidermal layers that are pushed to the surface when dead skin on the surface is shed, the basal cells of the hair bulb divide, pushing the cells at the root and shaft of the hair upward. outside when the hair grows. . HeBrand forms the central core of the hair, which is surrounded by theKortex, a layer of compressed keratinized cells covered by an outer layer of very tough keratinized cells known asCuticle. These layers are shown in a longitudinal section of the hair follicle (Figure \(\PageIndex{2}\)), although not all hairs have a medullary layer. The texture of the hair (straight, curly) is determined by the shape and structure of the cortex and, if present, the medulla. The shape and structure of these layers are in turn determined by the shape of the hair follicle. Hair growth begins with the production of keratinocytes by the basal cells of the hair bulb. As new cells are deposited in the hair bulb, the follicle pushes the hair shaft to the surface. Keratinization is complete when the cells are pushed to the surface of the skin to form the externally visible hair shaft. The outer hair is completely dead and made entirely of keratin. Due to this, our hair has no sensation. Also, you can cut or shave your hair without damaging the hair structure because the cut is superficial. Most chemical removers also work superficially; However, electrolysis and tearing attempt to destroy the hair bulb so that hair cannot grow.

    4.3: Accessory structures of the skin (3)

    The hair follicle wall consists of three concentric layers of cells. the cells of inner root sheaththey surround the root of the growing hair and reach just below the hair shaft. They originate from the basal cells of the hair matrix. Heouter root sheath, which is an extension of the epidermis, encloses the root of the hair. It is made up of basal cells at the base of the hair root and tends to be richer in keratin in the upper regions. Heglassy membraneIt is a thick, transparent connective tissue sheath that wraps around the hair root and connects it to the dermis tissue.

    Hair performs a variety of functions including protection, sensory information, thermoregulation, and communication. For example, the hair on the head protects the skull from the sun. Hair in the nose and ears and around the eyes (eyelashes) protects the body by trapping and excluding dust particles that may contain allergens and microbes. The eyebrow hairs prevent sweat and other particles from entering and bothering the eyes. Hair also has a sensory function due to sensory innervation from a hair root plexus that surrounds the base of each hair follicle. Hair is extremely sensitive to air movement or other disturbances in the environment, much more than the surface of the skin. This feature is also useful for detecting the presence of insects or other potentially harmful substances on the skin's surface. Each hair root is connected to a smooth muscle called the hair root.arrector pili which contracts in response to nerve signals from the sympathetic nervous system, causing the outer hair shaft to "stand up". The main purpose of this is to trap a layer of air to add insulation. This is visible in humans as goosebumps, and is even more noticeable in animals with thicker fur than most humans, such as cats. B. Dogs and cats that raise their fur when alarmed.

    Hair growth

    The hair grows and eventually falls out and is replaced with new hair. This happens in three phases. The first is theanagen Phase in which the cells of the hair root divide rapidly, pushing the hair shaft up and out. The duration of this phase is measured in years, typically between 2 and 7 years. Hecatagen The phase lasts only 2-3 weeks and marks a transition from active hair follicle growth. Finally during thetelogen In this phase, the hair follicle is at rest and no new growth occurs. At the end of this phase, which lasts around 2-4 months, another anagen phase begins. Basal cells in the hair matrix then produce a new hair follicle, which sheds the old hair as the growth cycle repeats. Hair normally grows at a rate of 0.3 mm per day during the anagen phase. On average, 50 hairs are lost and replaced every day. Hair loss occurs when more hair is lost than is replaced and can occur due to hormonal or dietary changes. Hair loss can also be caused by the aging process or the influence of hormones.

    Hair color

    Like skin, hair gets its color from the pigment melanin, which is produced by melanocytes in the papilla of the hair. Different hair colors result from differences in the type of melanin, which is genetic. As we age, melanin production decreases and hair tends to lose color, turning gray and/or white.

    nails

    The nail bed is a special structure of the epidermis found at the tips of the fingers and toes. Henail bodyarises in thebed of nails, and protects the tips of the fingers and toes, since they are the furthest extremities and the parts of the body subjected to the greatest mechanical stress (Figure \(\PageIndex{3}\)). In addition, the body of the nail forms a backing for picking up small objects with the fingers. The nail body consists of densely packed dead keratinocytes. The epidermis of this part of the body has developed a special structure on which nails can be formed. The body of the nail forms in theNagelwurzel, which has a matrix of proliferating cells from the basal stratum that allows for continued growth of the nail. the sidenail stitchingit overlaps the nail on the sides, helping to anchor the nail body. The nail fold that meets the proximal end of the nail body forms thecuticles, also calledeponych. The nail bed is rich in blood vessels, giving it a pink appearance, except at the base, where a thick layer of epithelium over the nail matrix forms a crescent-shaped region called the nail. swing(the "little moon"). The area below the free edge of the nail, furthest from the cuticle, is called the cuticle.hiponiquio. It consists of a thickened horny layer.

    4.3: Accessory structures of the skin (4)

    sweat glands

    when the body heats upsweat glandsproduce sweat to cool the body. Sweat glands develop from epidermal projections into the dermis. There are two types of sweat glands, each of which secrete slightly different products.

    AEccrine sweat glandIt is a type of gland that produces hypotonic sweat for thermoregulation. These glands are found all over the surface of the skin, but are particularly common on the palms of the hands, the soles of the feet, and the forehead (Figure \(\PageIndex{4}\)). They are tortuous glands found deep in the dermis, with the duct ascending to a pore on the surface of the skin where sweat is released. This type of sweat, released by exocytosis, is hypotonic and consists mainly of water, with some salt, antibodies, small amounts of metabolic waste, and dermicidin, an antimicrobial peptide. The eccrine glands are an important component of thermoregulation in humans and therefore help maintain homeostasis.

    4.3: Accessory structures of the skin (5)

    Aapocrine sweat glandit is usually associated with hair follicles in densely hairy areas, such as the armpits and genital regions. Apocrine sweat glands are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even reaching into the hypodermis, and the duct usually opens into the hair follicle. In addition to water and salts, apocrine sweat contains organic compounds that thicken the sweat and are subject to bacterial breakdown and subsequent odor. The release of this sweat is under both nervous and hormonal control and plays a role in the little-known human pheromone response. Most commercial antiperspirants use an aluminum-based compound as the main active ingredient to help stop sweat. When antiperspirant enters the sweat duct, aluminum-based compounds precipitate due to a change in pH, creating a physical blockage in the duct that prevents sweat from leaving the pore.

    oil gland

    Aoil glandIt is a type of sebaceous gland found throughout the body that helps lubricate and waterproof the skin and hair. Most of the sebaceous glands are connected to hair follicles. They create and discardSebum, a blend of lipids, to the skin's surface, naturally lubricating and softening the dry, dead layer of keratinized cells in the stratum corneum. The fatty acids in sebum also have antibacterial properties and prevent water loss from the skin in low humidity environments. Sebum secretion is stimulated by hormones, many of which are only activated during puberty. Therefore, during childhood, the sebaceous glands are relatively inactive.

    concept review

    Accessory structures of the skin include hair, nails, sweat glands, and sebaceous glands. Hair is made up of dead horny cells and gets its color from melanin pigments. Nails, also made of dead horn cells, protect the tips of the fingers and toes from mechanical damage. The sweat glands and the sebaceous glands produce sweat and sebum, respectively. Each of these fluids plays a role in maintaining homeostasis. Sweat cools the surface of the body when it overheats and helps remove small amounts of metabolic waste. The sebum acts as a natural moisturizer, keeping the dead, flaky outer layer of keratin healthy.

    review questions

    F. In response to stimuli from the sympathetic nervous system ________ the erector pili.

    A. are glands on the surface of the skin

    B. can cause excessive sweating

    C. are responsible for goosebumps

    D. secretes sebum

    Answer

    Answer: C

    Q. The hair matrix contains ________.

    A. the hair follicle

    B. the hair shaft

    C.die glass membrane

    D. A layer of basal cells

    Answer

    Answer: D

    P. Eccrine sweat glands ________.

    A. They are present in the hair

    B. are present on the skin all over the body and produce watery sweat

    C. produce sebum

    D. Act as a moisturizer

    Answer

    Answer:B

    F. Sebaceous glands ________.

    A. are a type of sweat gland

    B. associated with hair follicles

    C. It can work in response to touch

    D. Release of an aqueous solution of salt and metabolic wastes

    Answer

    Answer:B

    Q. Like hair, nails grow continuously throughout our lives. Which of the following is furthest from the center of nail growth?

    A. Nail bed

    B. Hyponichium

    C. Nagelwurzel

    D. Eponych

    Answer

    Answer:B

    critical thinking questions

    F. Explain the differences between eccrine and apocrine sweat glands.

    Answer

    A. Eccrine sweat glands are found throughout the body, particularly on the forehead and palms of the hands. You release a watery sweat mixed with some metabolic waste and antibodies. Apocrine glands are connected to hair follicles. They are larger than eccrine sweat glands and lie deeper in the dermis, sometimes even as far as the subcutaneous tissue. They emit thicker sweat that is often broken down by bacteria on the skin, leading to an unpleasant odor.

    F. Describe the structure and composition of the nails.

    Answer

    A. Nails are made up of densely packed dead keratinocytes. They protect the fingers and toes from mechanical stress. The nail body forms in the nail bed, which is located at the root of the nail. The nail folds, folds of skin that overlap laterally on the nail, secure the nail to the body. The crescent-shaped region at the base of the nail is the lunula.

    glossary

    anagen
    active phase of the hair growth cycle
    apocrine sweat gland
    Type of sweat glands associated with hair follicles in the armpits and genital areas
    arrector pili
    smooth muscle that is activated in response to external stimuli that pull on hair follicles causing the hair to "stand up".
    catagen
    Transitional phase that marks the end of the anagen phase of the hair growth cycle
    Kortex
    in the hair, the second or middle layer of keratinocytes derived from the hair matrix, as seen in a cross section of the hair bulb
    Cuticle
    in the hair, the outermost layer of keratinocytes derived from the hair matrix, as seen in a cross section of the hair bulb
    Eccrine sweat gland
    Type of sweat gland that is distributed over the entire surface of the skin; produces a hypotonic sweat for thermoregulation
    eponych
    Fold of the nail that meets the proximal end of the nail shaft, also called the cuticle
    outer root sheath
    outer layer of the hair follicle, which is an extension of the epidermis that encloses the hair root
    glassy membrane
    Connective tissue layer that surrounds the base of the hair follicle and connects it to the dermis
    They are
    Keratin filament that grows from the epidermis.
    hair wiggle
    Structure at the base of the hair root that surrounds the dermal papilla
    hair bellows
    cavity or sac from which the hair originates
    hair matrix
    Basal cell layer from which a tuft of hair grows
    his papilla
    Mass of connective tissue, blood capillaries, and nerve endings at the base of the hair follicle
    hair root
    Part of the hair that lies below the epidermis and is attached to the follicle
    hair shaft
    Part of the hair that lies above the epidermis but is not attached to the follicle
    hiponiquio
    thickened horny layer below the free edge of the nail
    inner root sheath
    innermost layer of keratinocytes in the hair follicle, which surrounds the hair root down to the hair shaft
    swing
    basal part of the nail shaft consisting of a crescent-shaped layer of thick epithelium
    Brand
    in the hair, the innermost layer of keratinocytes that originates from the hair matrix
    bed of nails
    Layer of the epidermis on which the body of the nail forms.
    nail body
    The main keratin plate that forms the nail.
    cuticles
    Epithelial fold that extends along the nail bed, also called eponychium
    nail stitching
    Epithelial fold that runs down the sides of the nail shaft, holding it in place
    Nagelwurzel
    The part of the nail that lies deep within the epidermis from which the nail grows
    oil gland
    A type of sebaceous gland found in the dermis throughout the body that helps lubricate and waterproof the skin and hair by secreting sebum.
    Sebum
    oily substance composed of a mixture of lipids that lubricates the skin and hair
    sweat gland
    Schweissdrüse
    telogen
    Resting phase of the hair growth cycle, initiated with catagen and ended by the initiation of a new anagen phase of hair growth

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