Integumentary system (Integumentum commune) = Skin and accessory structures Aleš Hampl December 2024 Integumentum commune = Body coverage Tela subcutanea = Subcutis - Hypodermis Cutis = Skin Epidermis = keratinizing stratified squamous epithelium Dermis = fibrous connective tissue Functional unit Largest body system 16% of body weight 1,5 to 2 m2 • hairs and nails • skin glands (sebaceous + sweat) • mammary gland Accessory structures Skin – overall composition • Epithelial – outer layer • Connective – underlies dermis • Smooth Muscle – goose bumps • Nervous – sensory receptors Skin = Combination of 4 main tissues Functions of the skin 1. Regulation of body temperature Cellular metabolism produces heat as a waste product . High temperature dilate surface blood vessels sweating Low temperature surface vessels constrict shivering 2. Protection physical abrasion dehydration ultraviolet radiation 3. Sensation touch vibration pain temperature 4. Excretion 5. Immunity/ Resistance 6. Blood Reservoir 8-10 % in a resting adult 7. Synthesis of vitamin D uv light aids absorption of calcium Epidermis - Layers • dead, flat cells full of keratin (25 to 100 layers) • corneodesmosomes • polar lipids - ceramides 5. Stratum corneum • more apparent in thick skin • 3-5 layers of clear cells • transitional state 4. Stratum lucidum 3. Stratum granulosum 2. Stratum spinosum 1. Stratum basale (germinativum) Desquamation=Maturation(about25days) • collumnar cells – one layer (keratines 5 and 14) • stratum germinativum • the only proliferating cells (stem, progenitor) • hemidesmosomes • polygonal cells (keratines 1 and 10) • 8-10 layers of keratinocytes • desmosomes – shrinkage - spines Keratinizing squamous stratified epithelium (keratinocytes – 4 or 5 layers) • 3-5 layers • tight junctions = zonulae accludentes • keratohyalin found in granules • cells beginning to die • keratohyalin and lamellar granules Easy to remember - Mnemonic Cancel Lab !!! Get Some Beer !!! Corneum Basale Spinosum Lucidum Granulosum Epidermis - Thin x Thick skin • entire body except thick skin areas • typical rhomboid area organization • stratum corneum – less than 25 layers of cells • stratum lucidum is absent • accessory struct.: sweat gl. + sebaceous gl. + hairs (except on lips, glans penis, labia minora) Thin skin Epidermis 50 – 100 mm Thick skin Epidermis 500 – 1000 mm • palms of hands and soles of feet = acral skin • skin ridges • stratum corneum – more than 100 layers of cells • stratum granulosum – expanded • accessory struct.: - eccrine glands only Epidermis Epidermis - Cell to Cell Adherence Basement Membrane Zonula adherens: Ca++ dependent cadherins that connect to actin Zonula occludens: tight junctions prevent diffusion across cells Macula adherens: made of desmosomes Gap junctions: communication for electric / metabolic function Hemidesmosomes: connect cells to basal membrane Junction: Dermis – Epidermis Hemidesmosomes Epidermolysis bullosa Stratum basale Stratum spinosum Dermal papilla (cross section) Dermis Epidermis – Stratum spinosum - Desmosomes Epidermis - Cell to Cell Adherence Epidermis – Non-keratinocyte cells • Keratinocytes - 90% – produce keratin • Melanocytes - 8 % – produces melanin pigment – melanin transferred to other cells with long cell processes • Langerhans cells – from bone marrow – provide immunity • Merkel cells – in deepest layer – form touch receptor with sensory neuron Epidermis – Melanocytes 1 Melanocyte Melanine Melanocytes: clearish cells in basal layer with dark nuclei ; ratio of 1 : 40 – epidermal melanin unit. Epidermis – Melanocytes 2 Epidermis – Melanocytes 3 Epidermis – Melanocytes 4 - Pigments Three pigments contribute to skin color Melanin – yellow to reddish-brown to black pigment, responsible for dark skin colors (Freckles and pigmented moles – result from local accumulations of melanin) Carotene – yellow to orange pigment, most obvious in the palms and soles of the feet Hemoglobin – reddish pigment responsible for the pinkish hue of the skin Do some people have more melanocytes than other people? NO !!!! Epidermis – Langerhans cells + Merkel cells Langerhans cell Merkel cell combines with disclike sensory nerve endings to make Merkel’s discs immune reaction that effects the skin and may serve defense mechanism for the body Migrate to lymph nodes Dermis (Corium) 1 Everything below the dermal-epidermal junction / basement membrane Connective tissue layer with contains blood vessels, nerves, sensory receptors, adnexal structures Dermis 2 = True skin – up to 4 mm on soles and palms Papillary layer (thin) Reticular layer (thick) Papillary dermis 1 Papillary Dermis Capillaries • loose connective t. & elastic fibers • dermal papillae which project into epidermis • anchors epidermis to dermis • contains Meissner’s corpuscles (touch) & free nerve endings (pain&temp) Papillary dermis 2 Two major types of fibers: – Type I Collagen – Elastic fibers: three types based on microfiber and elastin content Papillary dermis 3 Epidermal ridges (palms + soles) • reflect contours of the underlying dermal papillae • form the basis for fingerprints (and footprints) • increase firmness of grip by increasing friction • Dermatoglyphics - the study of the pattern of epidermal ridges Papillary dermis 4 Openings of sweat glands Papilae after peeling off epidermis Epidermal ridges • Dense irregular connective tissue • Sebaceous (oil) glands • Hair follicles • Ducts of sweat (sudoriferous) glands • Striae or stretch marks • Meissner’s corpuscles and Pacinian corpuscles (on lips, ext. genitalia, nipples) Reticular dermis + Accessory structures (Dermal appendages) Hair folliclePilar muscle M. arrector pili Sebaceous glands Eccrine glands Dermal glands Sweat Eccrine Tubular Apocrine Tubular to tuboalveolar Sebaceous Holocrine Branched acinar (alveolar) Dermal glands – Eccrine sweat glands (glandulae sudoriferae eccrinae) • Secretory part: Simple collumnar epithelium + myoepithelial cells • Ductular part: Two layered cuboidal epithelium Release to adjust body temperature Not on: red lips, glans penis, preputium, labia minora Eccrine sweat glands Three cell types • Dark cells: pyramid shaped with secretory granules line lumen of tubule • Clear cells: located toward basement membrane – secrete water and ions • Myoepithelial cells: spindle shaped contractile cells duct secretory part Eccrine sweat glands duct secretory part Eccrine sweat glands Dermal glands – Apocrine sweat glands (glandulae sudoriferae apocrinae) • Secretory part: Simple squamous to collumnar epithelium (depending on the secretoty cycle) + myoepithelial cells • Ductular part: Two layered cuboidal epithelium Always associated with hair follicle Influenced by hormones (sexual scent glands) Only on: axilla, areola mammae, scrotum, labia maiora, mons pubis, perianal area, meatus acusticus, vestibulum nasi, eye lid apocrine sweat gl. eccrine sweat gl. sebaceous gland. Apocrine sweat glands Apocrine sweat glands myoepithelial cells Dermal glands – Sebaceous glands (glandulae sebaceae) • Secretory part: multi layered epithelium, slow adipous degeneration (holocrine secretion) • Ductular part: multi layered squamous epithelium Usually associated with hair follicles Freely open on: red lips, glans penis, preputium, labia minora, eye lid (Meiboms glands) Not on: palms and soles Simple branched acinar glands Several acini empty into single duct Sebaceous glands sebaceous gland m. arrector pili hair follicle Sebaceous glands Sebaceous glands Mammary gland Modified and highly specialized type of apocrine sweat glands. Parenchyma • Ducts • Budding surface ectoderm • (since week 6) Stroma • Connective tissue • From mesenchyme axilo-inquinal line Supernumerary Breasts and Nipples • An extra breast (polymastia) or nipple (polythelia) occurs in approximately 1% of the female population - inheritable. • Supernumerary nipples are also relatively common in males. • Less commonly, supernumerary breasts or nipples appear in the axillary or abdominal regions of females developing from extra mammary buds that develop along the mammary crests. They become more obvious in women when pregnancy occurs. Development of the breast ductal tree Occurs mainly after birth At puberty changes in the hormonal secretions in females cause further development and structural changes within the glands. Secretions of estrogen and progesterone from the ovaries (and later from the placenta) and prolactin from the acidophils of the anterior pituitary gland initiate development of lobules and terminal ductules. Full development of the ductal portion of the breast requires glucocorticoids and further activation by somatotropin. Radial organization Mammary gland - Anatomical organization Lobe = 1 gland • total of 15 to 20 lobes • 1 lobe drained by 1 lactiferous duct LACTIFEROUS DUCT Lobule • drained by terminal ductulus = Terminal ducto-lobular unit Connective+Adipose tissue Sinuses (Cisterns) Ducts Mammary gland – After puberty – Nonlactating 1 • majority = connective tissue • the same basic architecture as the lactating (active) mammary gland • Secretion parts - alveoli are not developed, only small groups of cells at the endings of ductuli • Passages – branched + partly luminized Mammary gland – After puberty – Nonlactating 2 Mammary Gland – Lactating 1 • majority = glands • Ductuli: proliferate, branch, luminize (estrogens) • Secreting alveoli: proliferation, luminization (progesterone, prolactin) • connective tissue – only thin septa Mammary Gland – Lactating 2 • Secretion parts: filled by secretion (lipid droplets = apocrine, proteins = eccrine - exocytosis) • Passages: Ducts at the nipple: stratified squamous keratinizing ep. Lactiferous sinus and the lactiferous ducts: simple/stratified + cuboidal/collumnar ep. Smaller ducts: simple cuboidal ep. Mammary Gland – Lactating 3 Mammary Gland – Lactating 4 • The alveoli are composed of cuboidal cells partially surrounded by a meshwork of myoepithelial cells. • These secretory cells possess abundant RER and mitochondria, several Golgi complexes, many lipid droplets, and numerous vesicles containing caseins (milk proteins) and lactose. • Not all regions of the alveolus are in the same stage of production, because different acini display varying degrees of preparation for synthesis of milk substances. Electron micrograph of an acinar cell Mammary Gland – Lactating 5 Mammary Gland – Involuting 1 • atrophy and degeneration of the secretory cells • milk biosynthesis ceases • adipose cells occupy the empty space • the duct system remains • this process continues throughout menopause Mammary Gland – States of development Hair – Overall compostition Shaft: portion of hair above surface Root: portion of hair below surface Cuticle: outermost layer of hair Hair follicle: invagination of epidermis (to dermis / hypodermis) Hair bulb: at the base of the follicle (matrix - epithelial cells + melanocytes) Hair papilla: projection of dermal connective tissue into bulb - contains blood vessels and nerves Vellus x Terminal hairs Hair structure 1 Garther and Hiatt, Color textbook of histology, Elsevier ERS IRS CTS cortex Huxley + Henley layer External root sheat Hair structure 2 Cuticles Internal root sheat Hair bulb and papilla Hair – Color and Shape Hair growth cycle Bulge Active stem cells Active papilla Active papilla Active papilla Inactive papilla Anagen AnagenAnagen Katagen Telogen Anagen – months to years Katagen – 3 weeks (involution) Telogen – 3 months (resting) Nail 1 Nail plate (body) – „str. corneum“ Nail root – proximal part of the nail plate Nail matrix - str. basale + spinosum (dividing) Nail bed – str. basale + spinosum Nail 2 Area deep to the dermis • Loose connective tissue containing adipocytes, nerves, sensory receptors, arteries and veins (deep rete cutaneum) • Provides a flexible attachment to the underlying muscle and fascia Pacinian Corpuscle Hair bulb in the subcutis of the scalp Adipocytes Subcutis - Hypodermis Skin development Ectoderm • Epidermis • Accessory structures Mesenchyme (from mesoderm-dermatomes + unsegmented mesoderm-somatopleura) • Dermis • Hypodermis A – Month 1 – simple surface ektoderm B – Month 2 – two layered epithelium: basal layer + periderm (epitrichium) C – Month 3 – basal + intermediary + periderm layers (week 10-17 – formation of dermal ridges) D – Month 5 (end) – periderm replaced by stratum corneum Skin wound healing 1 Shallow cuts Deeper wounds cell migration contact inhibition Skin wound healing 2 Shallow cuts Deeper wounds Blood clot Inflammatory phase Migratory phase Maturation phase + Proliferative phase Fibrin forms clot Fibroblasts make granulation tissue hypertrophic scar = keloid Thak you for your attention! Questions and comments at: ahampl@med.muni.cz