Histology of Skin and Appendages PDF

ANA 11_MED: HISTOLOGY SKIN AND ITS APPENDAGES Gail Domecq C. Tanawit | NOVEMBER 30, 2023 TABLE OF CONTENTS Facts about the Skin I. Introduction VII. S...

ANA 11_MED: HISTOLOGY SKIN AND ITS APPENDAGES Gail Domecq C. Tanawit | NOVEMBER 30, 2023 TABLE OF CONTENTS Facts about the Skin I. Introduction VII. Skin Appendages Surface area: 1.5 - 2.0 m2 A. Structure of the Skin A. Hair Thickness: 0.5 - 3.0 mm B. Development of the B. Nails Growth rate of nail: 0.1mm/day Integumentary System C.Skin Glands Growth rate of hair: 1.5 - 2.2mm/week II. Epidermis VIII. Clinical Applications Lifespan of hair: A. Types of Cells A. Langer’s or Cleavage → Eyelashes & axilla: 4 mos B. Layers Lines → Scalp: 4 years C.Types of Skin B. Linea Gravidarum Note: Information was directly taken from Junqueira’s Basic Histology III. Dermis C. Epidermal Wound healing Text and Atlas, (2016). IV. Subcutaneous D. Deep Wound Healing FUNCTIONS OF THE SKIN Tissue/Hypodermis E. Aging Protective V. Structural Basis of Skin F. Rule of 9 in Burn Patients → Provides physical barriers against thermal and mechanical insults Color G.Dermatomes (friction and potential pathogens). VI. Innervation/Sensory → Skin lymphocytes and Antigen-presenting cells (APCs) Receptors ▪ Immune response A. Merkel Cells → Melanin B. Free Nerve Endings ▪ Protects cell nuclei from UV radiation C. Meissner’s Corpuscles → Permeability barrier D. Pacinian Corpuscles ▪ Against excessive loss/uptake of water E. Krause’s Corpuscles Sensory F. Ruffini Endings → Sensory receptors G.Hair Follicle Receptors ▪ Allows for constant monitoring of the environment Thermoregulatory → Maintenance of constant body temperature I. INTRODUCTION → Insulating components Integumentary System ▪ Fatty layer → Include the skin and its accessory structures including hair, nails, ▪ Hair on the head and glands, as well as blood vessels, muscles and nerves. → Mechanism for accelerating heat loss Dermatology ▪ Sweat production → Medical specialty for the diagnosis and treatment of disorders of ▪ Dense superficial microvasculature the integumentary system. Metabolic A. STRUCTURE OF THE SKIN → Synthesis of Vit D The skin (cutaneous membrane) covers the body and is the largest ▪ Needed in calcium metabolism organ of the body by surface area and weight. → Removal of excess electrolytes Area: 2m2 (22 ft2) → Fat storage in the subcutaneous layer Weight: 4.5 - 5kg (10-11 lb) Sexual Signaling → ~16% of body weight → Visual indicators of health involved in attraction between sexes. Thickness: 0.5 - 4mm → Sex pheromones produced by apocrine sweat glands and other → Thinnest skin: eyelids skin glands → Thickest skin: heels; average thickness is 1 - 2mm B. DEVELOPMENT OF THE INTEGUMENTARY SYSTEM Figure 1. Diagrammatic overview of Skin (Mescher, 2016). Two Major Layers Epidermis → Outer, thinner layer Dermis → Inner, thicker layer → Beneath is the hypodermis ▪ Subcutaneous (subQ) layer ▪ Attaches the skin to the underlying tissues and organs Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 1 of 12  12th week (d) → Hair follicles develop as downgrowths called hair buds. 14th week (e) → Hair bulbs form. → Sebaceous glands develop as outgrowths from the sides of the hair follicle. 16th week (f) → Mesoderm-filled papillae of the hair develop (where blood vessels and nerve endings develop) 18th week (g) → Cells in the hair bulb center develop into the matrix, forming hair. → Surrounding dermis develops into the dermal root sheath and arrector pili muscle. Other developmental stages not seen in the figure: 4-6 months → Tactile epithelial cells appear in the epidermis. 5 months → Lanugo (delicate fetal hair) is produced by hair follicles. → Sweat glands appear on the palms and soles. 10th week → Nails develop with a thick layer called the primary nail field. 9 months → Nails, composed of keratinized epithelium, reach the tips of the digits. II. EPIDERMIS Composed of keratinized stratified squamous epithelium → Epithelial invaginations from the epidermis ▪ Hair follicles, sebaceous glands, and sweat glands A. TYPES OF CELLS Four major types of cells → Keratinocytes, melanocytes, Langerhans cells, and Merkel cells Figure 3. Cells in the epidermis (Derrickson & Tortora, 2017) Keratinocytes 90% of the cells (most common) Produce keratin which is a tough fibrous protein that provides protection and waterproofing sealant → Keratin is a 10 nm intermediate filament Melanocytes Figure 2. Integumentary System Development (Derrickson & Tortora, About 8% of epidermal cells 2017) Present in stratum basale Rounded cells with dendrite-like branches Note: Information was directly taken from Derrickson & Tortora (2017). Produce melanin (eumelanins) that protects against the damage by Refer to Figure 2: UV radiation 4th week (a) Skin pigmentation → The epidermis originates from ectoderm, forming a single layer of Langerhans cells ectodermal cells. Intraepidermal macrophages 7th week (b) Present in stratum spinosum → The basal layer divides, creating the periderm, a protective layer Non-pigmented granular dendrocytes of flattened cells. Nucleus: indented at many places 11th week (c) Cytoplasm: contains rod-shaped granules → Basal layer forms an intermediate layer; epidermal ridges and Involved in immune responses against bacteria and viruses migration of cells into the dermis occur. Arise from the red bone marrow → Proliferation of basal cells eventually forms all layers of the epidermis present at birth. Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 2 of 12  Merkel cells → Cytoskeletal keratins Tactile epithelial cells → An important feature of all keratinocytes Found in stratum basale Differentiation Sensory cells innervated by sensory nerves → Moves cells upward and amount of keratin increases until keratin Abundant in fingertips, oral mucosa, and hair follicles filaments are ½ of the total protein in the superficial keratinocytes Function as sensitive mechanoreceptors (light touch sensation) Stratum spinosum Function in the sensation of touch with the adjacent tactile discs 8-10 layers of keratinocytes B. LAYERS Thickest layer The epidermis may contain four major layers (thin skin) or five major → Especially among the epidermal ridges layers (thick skin). Polyhedral cells with central nuclei with nucleoli Most regions of the body have thin skin. Cytoplasm is actively producing keratin Regions with greatest exposure to friction have thick skin (fingertips, Tonofibrils palms, and soles). → Visible bundles of keratin filaments → Converge and terminate at the numerous desmosomes holding the cell layers together Epidermis of thick skin subject to continuous friction and pressure has thicker stratum spinosum and more abundant tonofibrils and desmosomes Stratum granulosum Granular layer 3-5 layers of flattened cells Includes keratohyalin (basophilic masses) and lamellar granules (contains lipids and glycolipids) → Keratohyalin granules are non-membrane bound filaggrin masses → Lamellar granules are golgi-derived → Lamellar granules undergo exocytosis, producing lipid-rich, impermeable layer around cells against water loss Figure 4. Layers of Epidermis in thick skin (Mescher, 2016). Stratum lucidum Present only in thick skin (skin of the fingertips, palms, and soles) Thin, translucent layer of flattened eosinophilic keratinocytes No nuclei and organelles Cytoplasm contains packed keratin filaments Stratum corneum 15-20 layers of squamous, keratinized cells filled with birefringent filamentous keratin Composed of corneocytes or squames → Corneocytes: many sublayers of flat and dead keratinocytes → Continuously shed and replaced by cells from deeper strata as desmosomes and lipid-rich cell envelopes break down → Constant friction can stimulate the formation of a callus C. TYPES OF SKIN Figure 5. Layers of Epidermis in thin skin (Mescher, 2016). Note: Information was directly taken from Junqueira’s Basic Histology Text and Atlas, (2016). Refer to Figure 5: The interface between dermis and epidermis in thin skin is held together firmly by interlocking epidermal ridges or pegs (EP) and dermal papillae (DP). Dermis (D) of thin skin → more cellular and well vascularized compared to thick skin → with elastin and less coarse bundles of collagen Epidermis of thin skin → Stratum basale (B) ▪ one-cell thick containing most of mitotic cells → Stratum spinosum (S) ▪ synthesis of keratin and other proteins take place → Stratum granulosum (G) → Stratum corneum (C) ▪ consist of dead squames Keratinization → The accumulation of more and more protective keratin → occurs as cells move from the deepest layer to the surface layer Dandruff → An excess keratinized cells shed from the scalp Stratum basale Stratum germinativum Deepest layer Composed of single row of basophilic cuboidal or columnar keratinocytes Where continuous cell division occurs which produce all the other layers Tonofilaments Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 3 of 12  III. DERMIS →Between the collagen and elastic fibers are abundant A. CHARACTERISTICS proteoglycans rich in dermatan sulfate. Connective tissue containing collagen and elastic fibers Contains 2 layers Both dermal regions contain a rich network of blood and lymphatic → Outer Papillary region vessels. Nutritive vessels form 2 major plexuses: ▪ Consists of areolar connective tissue containing thin collagen 1. Subpapillary plexus and elastic fibers →Lies between the papillary and reticular dermal layers ▪ Dermal Papillae (incl. capillary loops), corpuscles of touch →Capillary branches extend into the dermal papillae and form a free nerve endings rich, nutritive capillary network just below the epidermis. → Deeper reticular region 2. Deep plexus ▪ Consists of dense irregular connective tissue containing →With larger blood and lymphatic vessels lies near the interface of collagen and elastic fibers adipose cells, hair follicles, nerves, the dermis and the subcutaneous layer sebaceous (oil) glands, and sudoriferous (sweat) glands Striae or stretch marks can appear if the skin is stretched too much Additionals: Lines of cleavage Dermal vasculature → “Tension lines” in the skin indicate the predominant direction of →Has a thermoregulatory function underlying collagen fibers ⬝ Which involves numerous arteriovenous anastomoses or Epidermal ridges shunts located between the two major plexuses. → Reflect contours of the underlying dermal papillae and form the ⬝ The shunts decrease blood flow in the papillary layer basis for fingerprints (and footprints) ⎼ To minimize heat loss in cold conditions → Their function is to increase firmness of grip by increasing ⎼ Increase this flow to facilitate heat loss when it is hot, friction ⎼ Helping maintain a constant body temperature. Dermatoglyphics Lymphatic vessels begin in the dermal papillae and converge to → Study of the pattern of epidermal ridges form two plexuses located with the blood vessels. The dermis is also richly innervated. →Sensory afferent nerve fibers form a network in the papillary dermis and around hair follicles, ending at epithelial and dermal receptors →Autonomic effector nerves to dermal sweat glands and smooth muscle fibers in the skin of some areas of postganglionic fibers of sympathetic ganglia →No parasympathetic innervation is present IV. SUBCUTANEOUS TISSUE/HYPODERMIS Connective tissue which may be adipose or fibrous, depending on the location The transition from dermis to hypodermis is irregular and poorly defined → No “boundary” Subcutaneous (subQ) layer (also called Hypodermis) Figure 6. Epidermis and Dermis Not part of the skin but, among its functions, it attaches the skin to the underlying tissues and organs Note: Information was directly taken from Junqueira’s Basic Histology Hypodermis (and sometimes dermis) contains lamellated Text and Atlas, (2016). (pacinian) corpuscles DERMIS → Detect external pressure applied to the skin Layer of connective tissue that supports the epidermis and binds it to the hypodermis Thickness varies with the region of the body and reaches its maximum of 4mm on the back Dermal papillae: →Surface of the dermis ⬝ Very irregular and has many projections (dermal papillae) that interdigitate with projections of the epidermis (epidermal pegs or ridges), especially in skin subject to frequent pressure, where they reinforce the dermal-epidermal junction. Basement membrane →Always occurs between stratum basale and the dermis →Follows the contour of the interdigitations between these layers. →Nutrients for keratinocytes diffuse into the avascular epidermis from the dermal vasculature through the basement membrane. Figure 7. Hypodermis Two sub-layers of the dermis with indistinct boundaries: 1. Papillary layer Note: Information was directly taken from Junqueira’s Basic Histology →Thin Text and Atlas, (2016). →Includes the dermal papillae Subcutaneous Tissue/Hypodermis/Superficial fascia →Consists of loose connective tissue The subcutaneous layer consists of loose connective tissue that ⬝ Types I and III collagen fibers binds the skin loosely to the subjacent organs, making it possible for →Fibroblasts the skin to slide over them. →Scattered mast cells, dendritic cells, and leukocytes. contains adipocytes that vary in number in different body regions →From this layer, anchoring fibrils of type VII collagen insert into vary in size according to nutritional state. the basal lamina, helping to bind the dermis to the epidermis. The extensive vascular supply at the subcutaneous layer promotes 2. Reticular layer rapid uptake of insulin or drugs injected into this tissue. →Consists of dense irregular connective tissue V. STRUCTURAL BASIS OF SKIN COLOR ⬝ Mainly bundles of type I collagen Variations in skin color arise from variations in the amounts of 3 →More fibers and fewer cells than the papillary layer. pigments →A network of elastic fibers is also present → Melanin, carotene, hemoglobin ⬝ Provide elasticity to the skin. Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 4 of 12  Melanin is a yellow-red or brown-black pigment produced by → Function as tonic receptors for sustained light touch and for melanocytes sensing an object’s texture. → Located mostly in the epidermis, where it absorbs UV radiation Free Nerve Endings → The amount of melanin causes the skin’s color to vary from pale In the papillary dermis and extending into lower epidermal layers yellow to red to tan to black Respond primarily to high and low temperatures, pain, and itching → The number of melanocytes are about the same in all people Also function as tactile receptors. ▪ Differences in skin color is due to the amount of pigment Root Hair Plexuses produced A web of sensory fibers surrounding the bases of hair follicles in → Nevus or mole the reticular dermis that detects movements of the hairs. ▪ A benign localized overgrowth of melanocytes B. ENCAPSULATED RECEPTORS → Albinism The encapsulated receptors are all phasic mechanoreceptors, ▪ Inherited inability to produce melanin responding rapidly to stimuli on the skin. → Vitiligo Four are recognized in human skin, although only the first two are ▪ Condition in which there is a partial or complete loss of seen in routine preparations melanocytes from patches of skin Meissner’s corpuscles Carotene Elliptical structures, 30-75 μm by 50-150 μm → Yellow-orange pigment Consisting of sensory axons winding among flattened Schwann → Found in the stratum corneum, dermis, and subcutaneous cells arranged perpendicular to the epidermis in the dermal papillae layer Initiate impulses when light-touch or low-frequency stimuli Hemoglobin against skin temporarily deform their shape. → Red color Numerous in the fingertips, palms, and soles but decline slowly in → Located in the erythrocytes flowing through dermal capillaries number during aging after puberty. VI. INNERVATION/SENSORY RECEPTORS Note: Information was directly taken from Dr. Tanawit’s lecture slides INNERVATION: the skin is richly innervated Served by a variety of: →Sensory nerve endings ⬝ Respond to a variety of modalities (pressure, vibration, heat, cold, itch, pain) →Motor nerve endings ⬝ Control blood flow, sweat secretion, piloerection. Free nerve endings →Terminate within the epidermis, penetrating almost to the stratum corneum Merkel’s touch corpuscles →At the base of the epidermis in thick (glabrous) skin of palms and soles Meissner’s corpuscles →Are encapsulated endings in dermal papillae, most common in palmar and plantar skin, especially in fingertips Pacinian corpuscles →Deeper in dermis, encapsulated by multilamellar, ovoid structures resembling small onions Figure 9. Meissner corpuscle. →Respond to deep pressure Meissner tactile corpuscles (TC) are specialized to detect light touch Krause’s endbulbs and are frequently located in dermal papillae (DP), partially surrounded →Mucocutaneous receptors by epidermis (E). They are elliptical, approximately 150-μm long, with →Encapsulated endings in dermis, especially associated with lips, an outer capsule (from the perineurium) and thin, stacked inner layers genital regions, nipples, and conjunctiva of modified Schwann cells, around which course nerve fibers. Ruffini endings →Have numerous fine branches from a single axon within the Lamellated (pacinian) corpuscles fluid-filled space of a single thin capsule Large oval structures, approximately 0.5 mm by 1 mm Hair follicle receptors Found deep in the reticular dermis and hypodermis →Unencapsulated nerve endings wrapped around hair follicles. → With an outer capsule and 15-50 thin → Concentric lamellae of flattened Schwann cells, and; → Collagen surrounding a highly branched, unmyelinated axon. Specialized for → Sensing coarse touch → Pressure (sustained touch) → Vibrations Distortion of the capsule amplifies a mechanical stimulus to the axonal core where an impulse is initiated. Are also found in the connective tissue of organs located deep in the body Figure 8. Meissner & Pacinian corpuscles → Including the wall of the rectum and urinary bladder, where they also produce the sensation of pressure when the surrounding A. UNENCAPSULATED RECEPTORS tissue is distorted. With its large surface and external location, the skin functions as an extensive receiver for various stimuli from the environment. Diverse sensory receptors are present in skin, including both simple nerve endings with no Schwann cell or collagenous coverings and more complex structures with sensory fibers enclosed by glia and delicate connective tissue capsules The unencapsulated receptors include the following: Merkel Cells Each associated with expanded nerve endings Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 5 of 12  Hair follicle → Tubular invagination of epidermis & dermis in which hair root resides → 3 layers (inner root sheath, outer root sheath, connective tissue sheath) Hair Bulb → Lower expanded end of hair follicle Hair papilla → The indentation at the base of hair bulb by part of the dermis Arrector Pilorum Muscle (Arrector Pili Muscle) → Smooth Muscle innervated by sympathetic nerve → Extends from papillary layer of dermis to the connective tissue sheath of a hair follicle → Contraction of muscle presses the sebaceous gland which squeezes out sebum → Formation of Gooseflesh Figure 10. Lamellated (pacinian) corpuscles. Lamellated (pacinian) corpuscles (PC) detect coarse touch or pressure and are large oval structures, frequently 1 mm in length, found among adipose tissue (A) deep in the reticular dermis or in the subcutaneous tissue. Here the outer connective tissue capsule surrounds 15-50 thin, concentric layers of modified Schwann cells, each separated by slightly viscous interstitial fluid. Several axons enter one end of the corpuscle and lie in the cylindrical, inner core of the structure. Movement or pressure of this corpuscle from any direction displaces the inner core, leading to nerve impulse. (X40; H&E) Krause end bulbs Simpler encapsulated, ovoid structures, with extremely thin, collagenous capsules penetrated by a sensory fiber. They are found primarily in the skin of the penis and clitoris where they sense low-frequency vibrations. Ruffini corpuscles Have collagenous, fusiform capsules anchored firmly to the surrounding connective tissue, with sensory axons stimulated by stretch (tension) or twisting (torque) in the skin. Figure 12. Components of Hair and Hair follicle. In Three dimensional view of the hair,, frontal section of hair root, transverse section of hair root. Retrieved from https://slideplayer.com/slide/14274248/ (2023) Figure 13. Structures of Hair follicle, shaft and root, and arrector pili muscle. Retrieved from Dr. Tanawit (2023) FIgure 11. Tactile receptors VII. SKIN APPENDAGES A. HAIR Composed of dead, keratinized epidermal cells Hair is Consist of: → Shaft → Root → Hair follicle → Epithelial root sheath (internal) → Dermal root sheath (external) Structure of Shaft and Root → Medulla Figure 14. Histological Section of Skin with epidermis, dermis, and hair → Cortex follicles. → Cuticle Retrieved from: Dr. Tanawit (2023) Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 6 of 12 Note: Information was directly taken from Junqueira’s Basic Histology Text and Atlas, (2016). Hair are elongated keratinized structure that form within epidermal invaginations, the hair follicle All skin has at least minimal hair except the glabrous skin of the palms, soles, lips, glans penis, and labia minora. Hair grows discontinuously with periods of growth followed by periods of rest, and this growth does not occur synchronously in all regions of the body or even in the same area. Hair has: → Hair bulb: terminal dilation; outermost cells are continuous with epithelial root sheath of the hair follicle, where 2 layers can be seen ▪ Internal Root Sheath completely surrounds the initial part of Figure 16. Sebaceous Gland its cells. Cells can have healthy nuclei or the hair root but degenerates above the level of the attached Pyknotic nuclei. Cells with pyknotic nuclei are old cells. sebaceous gland Retrieved from Dr. Tanawit (2023) ▪ External Root sheath covers the internal root sheath and Note: Information was directly taken from Junqueira’s Basic Histology extends all the way to the epidermis where it is continuous with Text and Atlas, (2016). the basal and spinous layers. Sebaceous glands are embedded in the dermis over most of the → Dermal papilla: inserts into the hair bulb and contains a capillary body except in thick, glabrous skin of the skin of the palms and network required to sustain the hair follicle. It is covered by soles Keratinocytes that are continuous with the basal epidermis. Sebaceous glands are branched acinar glands with several acini → Hair root converging at a short duct which empties into the upper portion of a → Hair shaft: hair extending beyond the skin surface hair follicle → Hair follicle: epidermal invaginations; has 2 layers Pilosebaceous unit is composed of: ▪ Connective tissue root sheath → Hair follicle ▪ Epithelial tissue root sheath → Associated sebaceous glands Structure of Shaft and Root In hairless regions, sebaceous ducts open directly onto the → Medulla: large, vacuolated, and moderately keratinized cells (in epidermal surfaces thick hair) Sebaceous glands acini undergo holocrine secretion → Cortex: heavily keratinized, densely packed cells Sebaceous glands have flattened epithelial cells on the basal → Cuticle: most peripheral cells of the hair root, it is a thin layer of lamina, which proliferate and are displaced centrally. heavily keratinized squamous cells covering the cortex → It undergoes terminal differentiation as a large, lipid producing sebocytes B. NAIL Sebocytes: Are composed of hard, keratinized epidermal cells located over → Filled with small fat droplets the dorsal surface of the ends of fingers and toes → Release their secretory product, lipid, by shrinking its nuclei and Each nail consists of: undergoing autophagy along with other organelles, and near the → Free edge duct the cells disintegrate → Transparent nail body (plate) with a whitish lunula at its base ▪ Sebum: A complex mixture of lipids including wax esters, → Nail root embedded in a fold of skin squalene, cholesterol, and triglycerides. Note: Information was directly taken from Junqueira’s Basic Histology ▪ Sebum functions to: Text and Atlas, (2016). − Help maintain the stratum corneum and hair shafts Nail Matrix: where nail root forms; where cells divide and move − Weak antibacterial property distally as it become keratinized − Antifungal property Nail root: the proximal part of the nail covered by a fold of skin, from Secretions from the sebaceous glands increases with puberty which epidermal stratum corneum extends. Stimulated by testosterone in men and ovarian and adrenal Cuticle or Eponychium: extended epidermal stratum corneum hormones in women Nail Plate: bound to a bed of epidermis Sudoriferous (Sweat) glands Nail bed: which contains only the basal and spinous epidermal → Numerous eccrine (or merocrine) sweat glands helps to cool layers the body by evaporating, and also eliminates small amounts of Hyponychium: distal end of the nail plate, free from the nail bed wastes C. SKIN GLANDS → Apocrine sweat glands Sebaceous glands → Located mainly in the axilla, groin, areolae, and bearded facial → Distributed all over the dermis of the skin, except for the palms regions of adult males and soles → Their excretory ducts open into hair follicles → Abundant in the scalp, face, around the apertures of the ear, ▪ Sweat is secreted during emotional stress and sexual nose, mouth & anus excitement → Holocrine in nature → Simple tubular glands lined by cuboidal epithelium → Number of alveoli connected to broad duct that opens into hair ▪ A duct communicates outwards through the overlying dermis follicle and the epidermis → Produces an oily secretion called sebum − Cells comprising the duct or conducting portion of the tubule forms a two-layered stratified cuboidal epithelium − Stained more intensely than secretory portion of the tubule − As fluid flows through the duct, its composition is modified by reabsorption of certain elements from the fluid e.g., for conservation of salt → Secretory portion lies deep in the dermis, where the tubule is twisted into a fairly compact tangle ▪ Secretory portion of a sweat gland is comprised of cells which are larger than those of the duct ▪ Simple cuboidal cells along with intersped myoepithelial cells which can expel sweat by contraction Figure 15. Sebaceous Gland Retrieved from Dr. Tanawit (2023) Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 7 of 12  Apocrine Sweat Glands → Largely confined to the skin, axillary, perineal regions → Development depends on sex hormones and is not complete and functional until puberty → Production of pheromones by apocrine glands in mammals and likely in humans in a reduced or vestigial capacity → Secretory: ▪ Larger compared to eccrine glands ▪ Simple cuboidal, eosinophilic cells with numerous secretory granules ▪ Secretions are protein rich products, viscous, and initially odorless but may acquire distinctive odor as a result of bacterial activity ▪ Undergo exocytosis and undergo MEROCRINE secretion → Ducts: Figure 17. Sudoriferous gland with eccrine (Left) and apocrine (right) ▪ Similar to eccrine sweat glands ▪ Open into hair follicle at the dermis instead of skin surface Retrieved from Dr. Tanawit (2023) → Innervation: ▪ Adrenergic Ceruminous Glands → Modified sweat glands located in the ear canal → Along with nearby sebaceous glands, they are involved in producing a waxy secretion called cerumen (earwax) which provides a sticky barrier that prevents entry of foreign bodies into the ear canal VIII. CLINICAL APPLICATIONS A. LANGER’S OR CLEAVAGE LINES Collagen fibers in the reticular region orient more in a single direction because of natural tension experienced by the skin resulting from bony projections, orientation of muscles, and movements of joints (Tortora & Derrickson, 2016). Lines along which the fiber bundles run Represent the natural lines along which the skin tends to split when penetrated. Incisions in the directions of these lines gape much less than those at right angles to them Figure 18. Sweat Gland with surrounding Fibrous and adipose connective tissue. Retrieved from Dr. Tanawit (2023) Note: Information was directly taken from Junqueira’s Basic Histology Text and Atlas, (2016). Sweat glands are long epidermal invaginations embedded in the dermis Two types of sweat glands, Eccrine and Apocrine. Eccrine sweat glands → Widely distributed in the skin → Most numerous in the foot soles → Composed of duct and secretory components ▪ Both are coiled and have small lumens → Auxiliary excretory organs to eliminate small amounts of nitrogenous waste and excess salts → Secretory: ▪ More pale-staining than the ducts ▪ Unusual stratified cuboidal epithelium with three cell types: − Clear cells: located on the basal lamina. Produce the Figure 19. Langer’s or Cleavage Lines sweat and have abundant mitochondria and microvilli to Retrieved from provide a large surface area https://www.marjoriebrook.com/blog/scars-in-the-line-of-tension/ − Dark Cells: filled with strongly eosinophilic granules.Lines Note: Information was directly taken from Principles of Anatomy and most of the lumen and do not contact with the basal lamina. Physiology, (2016). It undergoes MEROCRINE secretion to release mixture of For example, a surgical incision running parallel to the collagen glycoproteins that have bactericidal activity fibers will heal with only a fine scar. − Myoepithelial cells: found on the basal lamina which A surgical incision made across the rows of fibers disrupts the contract to move the watery secretion into the duct collagen, and the wound tends to gape open and heal in a broad, ▪ Ducts: thick scar and sometimes keloid. − Have two layers of more acidophilic cells filled with mitochondria and cell membranes rich Na+-K+ ATPase. B. LINEA GRAVIDARUM − Ducts absorb Na+ ions from the secreted water to prevent Also known as striae gravidarum excess loss of the electrolyte Rupture of fiber bundles of dermis due to excessive stretching − At the epidermis level, each duct merge with the stratum result in prominent white lines basale and sweat flow continues through the five Seen in anterior abdominal wall in pregnancy epidermal strata to an excretory sweat pore in the First present as flat, pink to red bands (striae rubra or immature surface of the skin striae) which becomes raised, longer, wider, and violet-red ▪ Innervation: − Cholinergic Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 8 of 12  Over a long period (months to years), marks fade and become hypopigmented (striae alba or mature striae) appearing parallel to Migration skin tension lines as scar-like, wrinkled, white, and atrophic marks. → Matrix metalloproteinases and other proteases from the migrating cells and macrophages facilitate cell migration Proliferative phase → Granulation tissue - new collagen-rich, well-vascularized tissue in the dermis - produced by proliferating fibroblasts and newly sprouted capillaries - replaces blood clot Final Stage or Maturation Phase → Epidermis reestablishes continuity but lost the ability to form new hair or glands → Granulation tissue undergoes remodeling and a more normal Figure 20. Linea Gravidarum vasculature is reestablished. Retrieved from Shutterstock.com → Collagen bundles and fibroblasts are much more abundant and C. EPIDERMAL WOUND HEALING disorganized than in uninjured skin, producing scar tissue at the wound site. Figure 21. Epidermal Wound Healing Retrieved from Principles of Anatomy and Physiology (Tortora & Derrickson, 2016) Note: Information was directly taken from Principles of Anatomy and Physiology, (2016). 1. Basal cells of the epidermis surrounding the wound break contact with the basement membrane 2. The cells then enlarge and migrate across the wound forming a sheet until advancing cells from opposite sides of the wound meet. 3. When epidermal cells encounter one another, they stop migrating due to a cellular response called contact inhibition. 4. As the basal epidermal cells migrate, a hormone called epidermal growth factor stimulates basal stem cells to divide and replace the ones that have moved into the wound. 5. The relocated basal epidermal cells divide to build new strata, thus thickening the new epidermis NOTE: Migration of the epidermal cells stops completely when each is finally in contact with other epidermal cells on all sides. D. DEEP WOUND HEALING Note: Information was directly taken from Junquiera’s Basic Figure 22. Major Stages of Cutaneous Wound Healing Histology and Atlas, (20211) Retrieved from Junquiera’s Basic Histology and Atlas, (Mescher, 2021) Skin E. AGING → can be easily repaired Most age-related changes begin at 40 YEARS OLD, when → capacity for repair is important since it is exposed and easily pronounced effects of skin aging become noticeable damaged Occur in the proteins of dermis Cutaneous Wound Healing Effects of Aging in the Integumentary System → overlapping stages that differ in duration depending on the size → Wrinkling-caused by reduced fibroblasts which produce collagen of wound and elastic fibers → can be caused surgically or accidentally → Decrease of skin’s immune responsiveness- Intraepidermal Stages of Cutaneous Wound Healing: macrophages dwindle in number and become less efficient Inflammation phagocytes → blood coagulates in the wound, which releases polypeptide → Dehydration and cracking of the skin-decreased size of growth factors and chemokines from disintegrating platelets sebaceous glands leads to dry and broken skin that is more → neutrophils and macrophage undergo diapedesis locally for susceptible to infection. bacteria and debris removal from wound → Decreased sweat production-Contributes to heat stroke in Epithelialization elderly → happens before inflammation is completed → Decreased number of functional melanocytes-resulting in gray → Epidermal basal layer remove desmosomes and hair and atypical skin pigmentation hemidesmosomes and migrate laterally beneath the blood → Loss of subcutaneous fat clot (increasingly desiccated eschar or scab) → General decrease in skin thickness → New cells may migrate from the bulge region of surviving → Increased susceptibility to pathological conditions hair follicles if much epidermis has been lost → Growth of hair and nails decrease, nails may also become → Growth of epidermal cells and fibroblasts → stimulated by brittle with age ( may be due to due to dehydration or repeated growth factors from macrophages and other cells from their use of cuticle remover or nail polish) binding sites in ECM proteoglycans. → 25% of males begin to show signs of hair loss by age 30 and about two-thirds have significant hair loss by age 60. Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 9 of 12  F. RULE OF NINE IN BURN PATIENTS G. DERMATOME Strip of skin supplied by a single spinal nerve Can help to detect and diagnose conditions or problems affecting your spine, spinal cord or spinal nerves Figure 23. Rule of 9 in Burn Child and Adult Patients Retrieved from https://i.pinimg.com/736x/88/1b/d3/881bd3e0485f24d3dd257a29f67834 35.jpg To estimate the extent of damaged skin in burn injuries Divides the body's surface area into percentages Example: The front and back of the head and neck equal 9% of the body's surface area. Degree of Burn Depth or Scale Characteristics First Epidermis pain, redness, mild swelling Second Epidermis pain, blisters, splotchy skin, + severe swelling Dermis: Papillary Figure 25. Dermatomes region (upper region Retrieved from https://clinicalgate.com/spinal-cord-and-nerve-roots/ of dermis IX. REVIEW QUESTIONS (FROM REFERENCE BOOKS) Third Entire thickness of white, leathery, relatively 1. Which of the following components of the epidermis provides skin (up to the painless sealant between adjacent cells? reticular region of a. Keratohyaline granules dermis) b. Glycolipids and lipids c. Keratin d. Desmosomes e. Adherent junctions 2. Which cells derive from precursors originating in the bone marrow and function as antigen-presenting cells in skin? a. Keratinocytes b. Langerhans cells c. Melanocytes d. Merkel cell e. Arrector pili 3. Cells responsible for producing the pigment for dark hair are located in which of following? a. The cortex of the hair shaft b. Throughout the hair shaft c. The internal root sheath of the hair d. The dermal papilla of the hair bulb e. The hair matrix (zone of dividing and differentiating cells) of the hair bulb 4. Which of the following separates the hair follicle from the Figure 24. Degrees of Burn connective tissue of the dermis? Retrieved from Principles of Anatomy and Physiology (Tortora & a. External root sheath Derrickson, 2016) b. Internal root sheath c. Glassy membrane d. Hair cuticle e. Medulla 5. Which structure typifies reticular dermis but not papillary dermis? a. Capillaries b. Dense irregular connective tissue c. Meissner tactile corpuscles d. Sweat gland ducts e. Type I collagen fibers 6. Which of the following best characterizes sebaceous glands? a. Its duct drains onto the skin surface. b. It releases its contents via holocrine secretion. c. It primarily secretes water and salts. d. Its secretory units are supplied by adrenergic stimulation. e. It is located typically in the reticular dermis Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 10 of 12 7. Myoepithelial cells aid in the secretory process of which of the following? a. Melanocytes b. Sebaceous glands c. Keratinocytes of the granular layer d. Eccrine sweat glands e. Apocrine sweat glands 8. A 52-year-old woman presents with severe blistering over her buttocks. Analysis of her serum demonstrates the presence of antibodies which by imunohistochemical techniques stain material located at the basement membrane of the epidermis in a biopsy of her skin. The underlying biological mechanism of her skin disorder involves an abnormality in which of the following structures? a. Macula adherens b. Gap junctions c. Hemidesmosomes d. Zonula occludens (tight junctions) e. Zonula adherens 9. A 64-year-old woman, who has always been proud of her suntanned, healthy look, is referred to a dermatologist with a blue-violet, painless, 1.5-cm lump in the skin of her left shoulder. The lump is firm and cannot be moved, and has grown very rapidly over the past few weeks. The mass is removed surgically and the pathologist diagnoses it as a Merkel cell carcinoma. If the UV radiation to which her skin was exposed affected the Merkel cells, what other cell type sharing the same specific epidermal layer might also be affected? a. Fibroblasts of the papillary layer b. Keratinocytes of the stratum granulosum c. Cells of tactile (Meissner) corpuscles d. Keratinized epithelial cells e. Basal stem cells for keratinocytes 10. A 37-year-old woman presents with a suspected Schwannoma. The radiology report indicates “a soft tissue mass to the right of L1 at the level of the L1 to L2 neural foramen.” The neurologist presses the base of a vibrating 128 cps tuning fork to the skin of the patient’s right and left thighs and asks her to describe the sensation. She asks the patient to close her eyes and then to tell her whether the tuning fork is vibrating or not. With that instrument the doctor is primarily testing the function of which of the following sensory receptors? a. Lamellated (Pacinian) corpuscles b. Kraus end bulbs c. Meissner corpuscles d. Merkel cells e. Free nerve endings X. REFERENCES Farahnik, B., Park, K., Kroumpouzos, G., & Murase, J. (2017). STRIAE GRAVIDARUM: Risk factors, prevention, and management. International Journal of Women’s Dermatology, 3(2), 77–85. https://doi.org/10.1016/j.ijwd.2016.11.001 Mescher, A. L. (2021). Junqueira’s basic histology text and atlas (16th ed.). McGraw-Hill. Tortora, G. J., &; Derrickson, B. H. (2017). The Integumentary System. In Principles of Anatomy and Physiology (15th ed.).John Wiley & Sons. Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 11 of 12  APPENDIX Figure 26. Summary of Skin and Subcutaneous Layers. (Mescher, 2016) Trans # 11 Group 6: Balmartino, De La Cruz, Gironella, Madrid, Nicolas, Santiago, Ton-ogan TH & TC: Acain 12 of 12