F18_02 SKIN (INTEGUMENTARY SYSTEM) SKIN SKIN (INTEGUMENTARY SYSTEM) Skin – the largest organ of the body, 15-20 % of total body weight, area 1,5-2 m2 FUNCTIONS OF SKIN •Barier protecting against physical abrasion, chemical irritants, pathogens, UV radiation, and desiccation • •Prevents water entry and loss • •Thermoregulation • •Reception of pressure and touch sensations • •Production of vitamin D • •Excretion (glands) SKIN COMPONENTS OF SKIN •Epidermis. Stratified squamous keratinized epithelium •Dermis. Composed of two layers of connective tissue containing blood vessels, nerves, sensory receptors, and sweat and sebaceous glands. Beneath the dermis is a layer of loose connective and adipose tissues that forms the superficial fascia of gross anatomy termed the hypodermis (subcutis). This layer is considered along with the skin, though technically it is not part of the integument. • Epidermal-dermal junction • •Scalloped margin at the interface of the epidermis and dermis, formed by interdigitations of: •Epidermal pegs. Downward projections of the epidermis •Dermal papillae. Upward, finger-like protrusion of connective tissue from the dermis • •This junction strengthens the attachment of the epidermis to the underlying dermis. • SKIN Subcutaneous tissue • •Also called hypodermis (subcutis) • •Not considered part of skin! • •Consists of loose connective tissue and adipose tissue, which can accumulate in large fatty deposits • •Loosely binds the skin to underlying structures • •May contain the bases of sweat glands and hair follicles • •Many sensory receptors, especially Pacinian corpuscles, are present. • Tela subcutanea V hypodermis – může být i husté bez tuku, není posun kůže po podkladu – nos, ušní boltec,… Řvp – volně pohyblivá kůže – penis, vičko, tuk chybí Jinak lalůčky tukového vaziva oddělené hustým kolagenní vazivem (síťovitě pospojované provazce – v okách tukové buňky) U prsní bradavky v areole,…– hladká svalovina SKIN CLASSIFICATION OF SKIN (Based epidermal thickness) •Thin skin •Covers entire body except palms and soles; 0.5 mm thick on the eyelid, 5 mm thick on the back and shoulders •Epidermis is thin, 0.075-0.15 mm thick, but the dermis varies from thin to very thick, depending on location. •Possesses hair with sebaceous glands •Sweat glands are present •Epidermis has not stratum lucidum •S. granulosum and s. corneum are much thinner SKIN CLASSIFICATION OF SKIN (Based epidermal thickness) •Thick skin • •Located on palms of the hands and soles of the feet; 0.8-1.5 mm thick •Epidermis is 0.4-0.6 mm thick •Hairless, no sebaceous glands •Sweat glands are present SKIN Layers of the epidermis and keratinization The epidermis is a stratified squamous, keratinized (dry) epithelium. It is continually renewed every 15-30 days. Rapid cell proliferation occurs primarily in the deepest layer (stratum basale) and daughter cells differentiate as they migrate toward the surface. This differentiation involves a process called keratinization, which results in a variably thick layer of nonliving cellular husks at the surface of the epidermis. All cells in the epidermis that undergo the keratinization process are called keratinocytes. Layers of the epidermis: •Stratum basale (germinativum) • A single layer of cuboidal to columnar shaped cells (keratinocytes) that rest on the basement membrane and undergo rapid cell proliferation. These cells contain intermediate filaments composed of cytokeratin (keratin proteins) (tonofilaments). SKIN Layers of the epidermis: •Stratum spinosum • Spiny cell layer; 3-10 cells thick. This layer is so-called because the cells are attached to one another by desmosomes, and the cellular shrinkage resulting from fixation produces the spine-like structures. These cells accumulate bundles of tonofilaments called tonofibrils. SKIN Layers of the epidermis: •Stratum granulosum • •two to four cells thick •cells synthesize basophilic, keratohyalin granules, which associate with the tonofibrils •Cells also accumulate lamellar bodies, which contain a lipid material that is secreted and serves as a sealant and penetration barrier between cells. •Cells also begin to lose other organelles. SKIN Layers of the epidermis: •Stratum lucidum A clear layer of non-nucleated, flattened cells that is only visible as a distinct layer in thick skin. In this region, the proteins contained in the keratohyalin granules mediate the aggregation of tonofibrils. This process occurs whether or not a distinct stratum lucidum is visible. •Stratum corneum • Variably thick layer of extremely flattened, cornified scales containing aggregated tonofibrils surrounded by a thickened plasma membrane. These cell remnants are sloughed off without damage to the underlying, living epidermal cells. Lysozymální hydrolytické enzymy – odbourávání organel ZVÝŠENÉ ODLUPOVÁNÍ – HYPERKERATÓZA Nefyziologická deskvamace – souvislé lamely – nadměrné slunění, popáleniny, odřeniny, otlaky – akutní mechanické namáhání kůže SKIN EPIDERMIS Cell types: •Keratinocytes •Keratinizing epidermal cells, major cell type in the epidermis •Function is to produce intermediate filaments composed of keratins •Amout of keratin filaments increases as the cells move upword • •Melanocytes •Langerhans cells •Merkel’s cells SKIN EPIDERMIS Cell types: •Keratinocytes • •Melanocytes. Melanin pigment-producing cells •Present in stratum basale and stratum spinosum •Rounded cell bodies with clear cytoplasm. Numerous "dendrite-like" processes insinuate themselves between the keratinocytes •Synthesize melanin, a dark brown pigment that is packaged into melanosomes and injected into keratinocytes •Melanin caps the keratinocyte nucleus, reducing damage from solar radiation. • •Langerhans cells • •Merkel’s cells SKIN EPIDERMIS Cell types: •Keratinocytes •Melanocytes •Langerhans cells. Macrophages that function in immunological skin reactions. •Merkel’s cells SKIN EPIDERMIS Cell types: •Keratinocytes •Melanocytes •Langerhans cells •Merkel’s cells. Touch receptors. SKIN DERMIS Composition: •Papillary layer 1. Located immediately beneath the basement membrane of the epidermis, forming the dermal papillae 2. Thin layer composed of loose connective tissue 3.Contains small blood vessels, nerves, lymphatics, and the sensory receptors, Meissner's corpuscles 4. •Reticular layer •Located between the papillary layer and the hypodermis •Thick layer composed of dense, irregular connective tissue •Contains larger nerves and blood vessels, glands, hair follicles, and the sensory receptors, Pacinian corpuscles and Ruffini end organs Vasculature of the dermis: •Papillary plexus located in the dermal papillae •Cutaneous plexus located in the reticular layer of the dermis •Arteriovenous anastomoses allow shunting of blood between papillary and cutaneous plexuses for temperature regulation. SKIN STRUCTURES ASSOCIATED WITH THE SKIN •Sensory structures •Nonencapsulated. Free nerve endings in the epidermis, responsive to touch, pressure, heat, cold, and pain • •Encapsulated pressure receptors •Meissner's corpuscle •Located at the apex of a dermal papilla •Consists of a coil of Schwann cells around a nerve terminal •Responds to light touch •Pacinian corpuscle •Located in the dermis and hypodermis •Consists of concentric layers of endoneurial cells around a nerve terminal •Responds to vibration and deep pressure •Ruffini ending •Located in the dermis •Consists of groups of nerve terminals surrounded by a thin connective tissue capsule •Responds to touch and pressure SKIN STRUCTURES ASSOCIATED WITH THE SKIN •Hair follicles •Hairs are elongated keratinized structures derived from invaginations of the epidermis (hair follicules) •Consist of a bulb at the base of the follicle that is located in the hypodermis or in the deep layers of the dermis. Internal and external sheaths surround the growing hair shaft as it passes though the dermis and epidermis. •An arrector pili muscle attaches a hair follicle to the papillary layer of the dermis. Contraction provides elevation of the hair, forming "goose-bumps." SKIN STRUCTURES ASSOCIATED WITH THE SKIN •Anagen – growth periods •Catagen – regression of follicle •Telogen – inaktivity • •Hair follicule •Epithelial tissue root sheath •Connective tissue root sheath • •Shaft (beyond epidermis) •Root •Hair bulb (terminal dilatation) •Dermal papila (with capillary network) • • •Papila is covered by cells that form the hair root and develop into the hair shaft. •A – the central cells produce large, vacuolated, moderately keratinized cells that form the medulla of the hair •B - laterally located cells, produce the cortex of the hair •C – cells forming hair cuticle •Peripheral epithelial cells develop into the internal and external root sheaths. •The external root sheath is continuous with the epidermis •The cells of the internal root sheath disappear at the level of the opinings of the sebaceous gland ducts. •Melanocytes •in the hair bulb •among the keratinocytes •transfer melanin granules into the epithelial cells • •Glassy membrane •Separating the hair follicle from the dermis •An acellular hyaline layer, the thickened basement membrane SKIN STRUCTURES ASSOCIATED WITH THE SKIN •Nails • •Keratinized epithelial cells on the dorsal surface of the fingers and toes •Consist of a nail plate that corresponds to the stratum corneum of the epidermis. This plate rests on the nail bed, consisting of cells corresponding to the stratum spinosum and stratum germinativum. •Nail root lies in an epidermal fold, whose stratum corneum forms the eponychium (cuticle) •Nail matrix lies beneath the nail root and is the germinative portion of the nail. •The hyponychium, a thickened epidermis, secures the nail at the fingertip SKIN STRUCTURES ASSOCIATED WITH THE SKIN •Sebaceous glands •Simple, branched acinar glands •Usually secrete into a hair follicle •Produce sebum, an oily secretory product, released by the holocrine mode of secretion •Absent from thick skin • •Sweat glands •Simple, coiled tubular glands •Contain myoepithelial cells, which are specialized cells that contract to aid in the expulsion of the sweat •Types of sweat glands •Merocrine or eccrine. Located in all regions of the body except the axillary and anal regions; produce a watery secretion that empties onto the surface of the epidermis •Apocrine. Restricted to the axillary, areolar, and anal regions; much larger than eccrine sweat glands with a broader lumen. Produce a viscous secretion that empties into the hair follicle. V pubertě vlivem hormonů plný vývoj, více vyvinuty u žen, ve stáří regrese F18_17 F18_18 Sweet gland, simple coiled tubular gland. H&E stain Sweet gland; the duct lined by stratified cuboidal epithelium; myoepithelial cells surround the secretory portion (contraction helps tho discharge the glandular secretion). H&E stain V pubertě vlivem hormonů plný vývoj, více vyvinuty u žen, ve stáří regrese