Histology LC 2: Skin And Its Appendages (University of Northern Philippines Batch 2026) PDF

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC 2 SKIN AND ITS APPENDAGES COLLEGE OF MEDICINE, BATCH 2026 Tra...

UNIVERSITY OF NORTHERN PHILIPPINES HISTOLOGY LC 2 SKIN AND ITS APPENDAGES COLLEGE OF MEDICINE, BATCH 2026 Transcribers: Gadut, Gorospe, Kwaw, Lucas Dr. Ana Patricia Villanueva-De Grano Editors: Gadut, Gorospe, Kwaw, Lucas Sept. 12, 2022 SKIN APPENDAGES I. SKIN APPENDAGES II. HAIR II. HAIR A. HAIR FOLLICLE MORPHOLOGY B. HAIR FOLLICLES C. HAIR BULB D. ANATOMY OF HAIR FOLLICLES Can be found all over the body except for the thick skin of the E. HAIR SHAFT soles and palms F. TYPES OF HAIR Plays a vital role in body’s homeostasis. G. TYPES OF HAIR GROWTH ✓ Hair – regulates body temperature H. HAIR GROWTH I. HAIR SHAPE ✓ Hair Follicles – essential for the growth and J. HAIR COLOR development of hairs. K. CLINICAL CORRELATION ✓ Hair Bulb – stem cells for differentiation into various III. SEBACEOUS, ECCRINE AND APOCRINE GLANDS cell types that will make up the hair. A. SEBACEOUS GLAND 1. SEBUM 2. CLINICAL CORRELATION 3. ARRECTOR PILI MUSCLE B. ECCRINE GLNADS 1. SECRETORY OIL 2. DERMAL DUCT C. APOCRINE GLANDS 1. CLINICAL CORRELATION IV. NAILS A. NAIL STRUCTURE B. CLINICALCORRELATION V. BLOOD SUPPLY AND INNERVATION A. BLOOD SUPPLY B. INNERVATION AND NERVE ENDINGS VI. THICK SKIN VS. THIN SKIN VII. REFERENCE(S) I. SKIN APPENDAGES First developed during the 2nd trimester of the intrauterine development. Roots in the surface of simple epithelium into the developing subepithelial layers of mesoderm. Formed in the subcutaneous tissue, dermis, and epidermis. Appendages includes: ✓ Hair ✓ Hair Follicles ✓ Sebaceous Glands ✓ Sweat Glands ✓ Eccrine Glands A. HAIR FOLLICLE MORPHOGENESIS ✓ Apocrine Glands ✓ Nails FUNCTIONS: Mesenchymal cells in the fetal dermis collect immediately below Reserve epidermis in the re-epithelialization after skin injury. the basal layer of the epidermis (By migration of Keratinocytes from the adnexal epithelium of Epidermal buds grow down into the dermis the skin.) Developing follicles forms at an angle to the skin surface and Example: Wound on the scalp and face will heal rapidly in the continues to grow downwards. process of re-epithelialization due to the presence of numerous At the base, the column of cells widens forming the bulb and Pilosebaceous Unit (Hair Follicles, Sebaceous Gland & Arrector surrounds small portion of mesenchymal cells. Pili) compared to the non-hairy skin of the back. Page 1 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano 3 Vertical Segments of Hair Follicle ✓ Infundibulum - uppermost portion; above sebaceous gland - extends to the opening of sebaceous glands ✓ Isthmus - between the sebaceous gland and insertion part of the arrector pili muscle - Internal Root Sheath is fully keratinized and sheds within this segment ✓ Inferior Segment - location of hair bulb C. HAIR BULB Base, bulbous expansion and invaginated by Dermal Papillae (a B. HAIR FOLLICLE tough vascularized loose connective tissue). Highly vascularized Contains melanocytes 2 Buds are formed along one side of the Fetal Follicle: It has Cell Matrix (rapidly proliferating cells that produces the ✓ Upper Bud – develops into sebaceous gland hair shaft, internal root sheath & external root sheath) ✓ Lower Bud – becomes attachment for the arrector pili Subjected to cycle of involution and regeneration throughout life muscle 3rd bud was formed in the opposite side of the Fetal Follicle which gives rise to the Eccrine Sweat Gland. Pilosebaceous Unit compose of: ✓ Hair Follicle ✓ Sebaceous Gland ✓ Arrector Pili Muscle D. ANATOMY OF HAIR FOLLICLE Hair Follicle grow in an upward direction from the hair bulb towards the skin surface 5 Epithelial Layers was formed. ✓ The 3 inner layers undergo keratinization to form the hair shaft or the hair, these includes the: - Central Medulla - Peripheral Cortex - Hair Cuticle Page 2 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano ✓ The 2 layers form the Internal Root Sheath & External ✓ 2 layers of Internal Root Sheath Root Sheath ▪ Henle Layer Tubular Structure – formed by perifollicular connective tissue - thin, paler epithelial stratum and epithelium; also invaginates the epidermis. - outer single layer of cuboidal cells The hair follicle is surrounded by Internal Root Sheath & External - indirect contact with the outermost parts Rooth Sheath of hair follicle which present a downward Grows up to 0.37 mm/day or approximately 1 cm/month. growth of the epidermis ▪ Huxley Layer - thin, granular epithelia stratum - single of double layer of flattened cells that will form the middle plate of internal root sheath. *These 2 layers become indistinguishable as they fused with one another and merge to the cells in the expanded part of the hair follicle, called the hair bulb. External Root Sheath ✓ Separates hair follicle from the dermis hyaline layer. ✓ Separated from the connected tissue sheath by a glassy membrane. ✓ Homogenous appearance ✓ Covers the internal root sheath and extends all the way the epidermis until to the basal & spinous layer. ✓ External epithelial layer merges with the epidermis of the sebaceous gland. Internal Root Sheath ✓ Recognized by its prominent pores ✓ Contains Eosinophilic Granules (Keratohyalin Granules) ✓ Surrounds the initial part of the hair but degenerates above the level of the sebaceous glands. Page 3 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano E. HAIR SHAFT Contains melanin pigment F. TYPES OF HAIRS Present in germinative layer of the hair bulb Composed of cuticle, cortex & medulla When the hair shaft is matured, the thin pale stained cuticle Lanugo layer surrounds the pigmented cortex and pale medulla. ✓ Fetal or newborn hair ✓ Hair Cuticle – thin, pale stained ✓ Characterized by fine hair - surrounds the cortex and medulla ✓ Replaced by vellus and terminal hairs ✓ Cortex – peripherally to the medulla Vellus - contains cuboidal cells ✓ Fine, light colored - cells undergo differentiation into keratin filled ✓ Narrow hair shaft cell ✓ Thin inner root sheath ✓ Medulla – central part of the shaft ✓ Rooted in papillary or reticular dermis - contains large vacuolated cells present only in thick hairs Terminal Hairs ✓ Coarse, thick ✓ Dark (except blondes) G. STAGES OF HAIR GROWTH Occurs in cyclical manner Follicle is an independent unit * Humans does not shed synchronously ✓ Anagen - Active Growth Phase - 2 to 6 years - Long period of mitotic activity and growth Page 4 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano ✓ Catagen - Transition Phase - 1 to 2 weeks - Brief period of growth and regression of the hair bulb ✓ Telogen - Resting Stage - Dermal papilla separated from follicle - Long period of in activity causing the hair to shed before turning anagen stage. I. HAIR SHAPE Dimensions and curvature of the inner root sheath determine the shape of the hair. Scalp hairs of African and Caucasians descent is oval causing their hair to be curly. Pubic hair, facial hair & eyelashes are oval in shape. H. HAIR GROWTH Anagen Hairs ✓ Active growth phase ✓ Up to 0.37 mm/day growth on scalp ✓ Pigmented bulb in internal root sheath Catagen Hairs ✓ Transition Phase ✓ Involution ✓ Numerous apoptotic cells in the outer root sheath Telogen Hairs ✓ Resting Phase ✓ Eyelashes have a short anagen and long telogen ✓ Non-pigmented bulb with a shaggy lower boarder (Flame thrower-like appearance) J. HAIR COLOR Depends on degree of melanization Also in the distribution of melanosomes with the hair shaft Hair bulb contains melanocytes that synthesizes melanin Melanin is transferred to the keratinocytes of the bulb matrix; the process is called pigment donation. Page 5 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano K. CLINICAL CORRELATION Aloepecia Areata ✓ Autoimmune ✓ Peribulbar Lymphocytic Infiltrates ✓ Causing the arrest of anagen phase A. SEBACEOUS GLANDS Telogen Effluvium ✓ Premature termination of anagen phase ✓ Increase telogen phase ✓ Most common type of hair loss Sebaceous Gland ✓ Characterize by excessive and diffused loss of hairs Associated with hair follicles (pilosebaceous unit) Lateral protrusions from the hair follicle Simple of branched alveolar in morphology appearing like a bunch of grapes (the acini of these glands are classic examples of holocrine secretion) Holocrine gland – total disintegration of secretory cells with sebum ✓ secretes an oily mixture of lipids into hair follicles known as Sebum. ✓ Sebum production is an example of holocrine secretion because the entire cell dies and contributes to the secretory products. Basal layer of flattened epithelial cells on the basal lamina III. SEBACEOUS, ECCRINE AND APOCRINE GLAND Sebocytes – filled with small fat droplets Near the duct, the cells disintegrate releasing the main secretory product, the sebum. The skin includes 3 types of exocrine glands: the sebaceous, Sebaceous glands are embedded in the dermis over most of the eccrine sweat gland and the apocrine sweat gland. body, except in the thick, glabrous skin of the palms and soles. Page 6 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano There is an average of about 100 such glands per square centimeter of skin, but the frequency increases to 400-900/cm2 in the face and scalp Sebaceous glands are branched acinar glands with several acini converging at a short duct that usually empties into the upper portion of a hair follicle. A micrograph shows the gland’s capsule (C) and differentiates sebocytes (S) at higher magnification. A section of a pilosebaceous unit shows acini composed of large sebocytes (S), which undergo terminal differentiation by filling with small lipid droplets and then disintegrating near the ducts (D) opening at the hair (H). 1. Sebum Mixture of lipids (wax, esters, squalene, cholesterol, and triglycerides) Increases at puberty Stimulated by androgens Secretion from sebaceous glands increases greatly at puberty, stimulated primarily by testosterone in men and by ovarian and adrenal androgens in women. Sebaceous Gland (4) associated on Hair Follicle: Stain: hematoxylin and Sebum helps maintain the stratum corneum and hair eosin. Medium magnification. shafts and exerts weak antibacterial and antifungal properties. 2. Clinical Correlation: Helps maintain the stratum corneum and hair shaft Acne vulgaris Found everywhere on the body except the palms and o Inflammation of the pilosebaceous unit soles Seborrheic dermatitis (dandruff) ✓ More abundant in the scalp, face. Midline of o Found in areas rich in sebaceous glands the back, perineum, and orifices of the body o form of eczema that appears on areas with ✓ They are also found in non- hairy sites which high concentration of sebaceous glands like the includes the: upper back, nose, scalp. - Eyelids: Meibomian glands - Buccal mucosa & vermilion of lip: Fordyce spots - Areola of women: Montgomery glands - Labia minora & glans: Tyson glands Acne Vulgaris (left) and Seborrheic dermatitis (right) Page 7 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano 3. Arrector Pili Muscle ✓ Each hair follicle has arrector pili muscle fibers ✓ It consists of a bundle of smooth muscle fibers. This muscle inserts at one end into the sheath of the follicle just below the sebaceous gland and the other end into the dermal papillary area beneath the epidermis. ✓ Part of the pilosebaceous unit ✓ Oblique bands of smooth muscle inserted into the middle of hair follicle ✓ Controlled by the autonomic nervous system ✓ The contraction of arrector pili muscle erects the hair shaft. It depresses the skin where it inserts because of the connections it has to the dermal layer. It will produce Goose-bumps” results to the contraction of arrector pilli muscle a small bump on the surface of skin often called your goosebumps. B. ECCRINE GLANDS ✓ Small bump on the surface of skin often called your goosebumps. ✓ Contraction: “goose flesh appearance” Found in palms, soles, and forehead Merocrine/eccrine in type Secretion discharged by exocytosis Simple coiled tubular in morphology Stimulus is heat, under control of hypothalamic thermostat (Sweating is a physiologic response to increased body temperature during physical exercise or thermal stress and is the most effective means of temperature regulation of humans) The secretory component is generally pale staining than the dots and consists of an unusual stratified cuboidal epithelium widely distributed in the skin and are most numerous on the foot soles (620/cm2) Collectively the 3 million eccrine sweat glands of the average person approximately equal the mass of a kidney and produce as much as 10 L/d, a secretory rate far exceeding that of other Arrector Pili Muscle exocrine glands. Sweat: ✓ Duct opens into epidermis as sweat pore, re- absorb sodium without water 1. SECRETORY DUCTS Only one distinct layer composed of secretory cells 3 distinct cell types: ✓ Clear cells (secretory) - Produce sweat - Transports interstitial fluid from the dermis, either directly into the gland’s lumen or into intercellular canaliculi that open to the lumen. ✓ Dark cells (mucoid) - Eosinophilic granules at the lumen - Merocrine secretion to release a poorly understood mixture of glycoproteins with bactericidal activity. ✓ Myoepithelial cells - At the basal lamina Arrector PilliMuscle (6). Stain: hematoxylin and eosin. Medium - Contract to move watery substance to the magnification. duct Page 8 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano basal lamina (BL) to propel sweat into the duct. Irregular pyramidal cells 2. DERMAL DUCT called dark cells (D) border the lumen (L) and are filled with the electron Double layer (2 layers of acidophilic cells) dense, eosinophilic secretory granules that release bactericidal peptides It opens into the epidermis as a sweat pore, and other components of innate immunity. Columnar clear cells (C) on the and it is biochemically active as it modifies the basal lamina rapidly transport water from interstitial fluid in the capillary- rich dermis directly into the lumen or into intercellular canaliculi (IC) composition of sweat because its cell continuous with the lumen. Na+ ions are recovered from this fluid through membrane is rich in Na-K ATPase. Thus, the action of cells in the ducts. X6500. reabsorbing Na ions prevent the excessive loss of electrolyte. Eosinophilic lumen C. APOCRINE GLANDS Na+ reabsorption Merges with the stratum basale to form the sweat pore Secretory cells are low cuboidal Have more numerous myoepithelial cells myoepithelial cells - bring out secretory contents Non-functional until puberty Become functional at puberty when the sex hormones are produced The production of pheromones by apocrine glands is well established in many mammals. It is innervated by adrenergic nerve endings, whereas eccrine sweat glands receive cholinergic fibers. Viscous secretion ✓ initially odorless – unpleasant odor (after bacterial decomposition) - secretion itself is not odorous, it’s the bacterial decomposition that conjures/confers Histologically eccrine glands have small lumens in the secretory the bad smell components (S) and ducts (D), both of which have an irregular stratified ✓ stimuli: emotional stress, sympathetic discharge cuboidal appearance. Both clear and acidophilic cells are seen in the (innervated by adrenergic nerve endings vs. stratified cuboidal epithelium of the secretory units. The box indicates an cholinergic fiber in eccrine) area with such cells like that shown ultrastructurally in part (b). The secretory portions (S) of apocrine sweat glands have lumens that are much larger than those of eccrine sweat glands. The ducts (D) of apocrine glands also differ from those of eccrine glands in opening into hair follicles (H) rather than to the epidermal surface. 1. CLINICAL CORRELATION Hyperhydrosis ✓ Excessive sweating (eccrine glands) Bromhidrosis ✓ Offensive odor from apocrine gland secretions TEM of these important thermoregulatory structures reveals three cell and bacterial flora types in their secretory portions. Myoepithelial cells (M) are present at the Page 9 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano Hyperhidrosis (left) and Bromhidrosis (right) Comparison of Eccrine Gland & Apocrine Gland Eccrine Sweat Gland (a) and Aprocrine Sweat Gland (b) IV. NAILS Both glands are coiled and tubular but apocrine glands are less coiled, have wider lumen, and have more myoepithelial cells. Dorsal surfaces of terminal phalanges A. NAIL STRUCTURE Nail Apparatus ✓ Nail plate ✓ Specialized epithelia: - Proximal nail fold - Nail matrix - Nail bed - Hyponychium Nail Root ✓ Proximal part of the nails ✓ Covered by a fold of skin (PROXIMAL NAIL FOLD) → CUTICLE / EPONYCHIUM ✓ From which the epidermal stratum corneum extend as cuticle or the eponychium. ✓ Forms the nail matrix ✓ Also known as the “Germinal Matrix” Eccrine & Apocrine sweat gland: secretory and excretory portions of Nail Matrix each sweat gland. Stain: hematoxylin and eosin. Medium magnification. ✓ It is the area where fingernails and toenails start to grow ✓ A distal movement by proliferation and differentiation of epithelium Page 10 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano ✓ Nail Root matures and hardens to form the ✓ A semilunar area of proliferative ventral Nail Plate surface of the nail groove ✓ It is the skin underneath the nails ✓ 3 mm/month (fingernails) and 1 mm/month (toe nails) in which cells divide Hyponychium more distally and become keratinized in the Distal end of the plate (become free of nail process similar to hair formation but bed at the epidermal fold), it is the skin just without keratohyaline granules under the free edge of the nail ✓ Complete replacement of a finger nail will require 6 months while for toe nail its 12 to B. CLINICAL CORRELATION 18 months. Nail Pitting ✓ Abnormal keratinization of the nail matrix Nail Structure Nail Pitting Lunula Melanonychia ✓ Crescent-shaped white area ✓ Brown-Black discoloration of the nail ✓ Opaque nail matrix and immature nail plate plate below it ✓ Nail root matures and hardens to form nail plate. Melanonychia Lunula V. BLOOD SUPPLY & INNERVATION Nail Plate ✓ Dense keratinized appendage ✓ Hard keratin A. BLOOD SUPPLY ✓ Continuous growth in matrix pushes the nail Cutaneous plexus: between the dermis and subcutis plate forward over the nail bed. ✓ Larger blood vessels ✓ t is the visible part of the nail from the lunula Subpapillary or superficial plexus: between the papillary and to the free edge reticular dermis Nail Bed ✓ Capillaries, end arterioles, venules ✓ Contains only basal and spinous epidermal layers (the last 2 of the epidermal layers) Page 11 of 12 [PHYSIOLOGY] 1.02 SKIN AND ITS APPENDAGES – Dr. Ana Patricia Villanueva-De Grano Glomus bodies: special type of AV anastomosis for temperature regulation; fingers, toes, and nails. Meissner corpuscles (left) and Pacinian corpuscles (right) VI. THIN SKIN VS. THICK SKIN Thick skin ✓ Palms of hands, fingers, soles, feet ✓ Thickness of epidermis considerable ✓ Abundant sweat glands Regulation of temperature by AVA in the skin tissue ✓ No pilosebaceous unit ✓ Grooves and ridges prominent because of tall dermal Small arteries (deep vascular plexus) and arterioles (dermis) papillae possess 3 layers: ✓ Numerous arterio-venous anastomoses ✓ Intima – composed of endothelial cells Thin skin and an internal elastic lamina ✓ Other regions except palms, soles, fingers, toes ✓ Media – contains collagen, elastic ✓ Thin epidermis fibers, and several concentric layers of ✓ Small number of sweat glands smooth muscle cells bounded by an ✓ Presence of pilosebaceous follicles external elastic lamina (in arteries) ✓ Lacks ridges and grooves with checkered networks of ✓ Adventitia – composed of fibrocytes, lines collagen, and elastic fibers ✓ Absent or few arteriole-venous anastomosis Walls of veins are generally thinner compared to arteries and less clearly divided into three classic layers Artery and Vein VII. REFERENCES Nerve Endings ✓ Both efferent and afferent nerve supplies. Mescher, A.L. (2016). Junqueira’s Basic Histology Text and Atlas. 14th Edition. ✓ Free nerve endings. McGraw-Hill Education. - Can be myelinated or unmyelinated Dr. De Grano’s PPT Presentation: Skin Appendages. S.Y. 2022-2033. University ✓ Meissner Corpuscle (Mechanoreceptor) consisted of Northern Philippines-College of Medicine these nerve endings specialized for pain, itch, and temperature sensation ✓ Prominent in papillary dermis of fingers, toes, soles, and palms. ✓ Pacinian corpuscle consisted these nerve endings specialized for deep pressure and vibration (deep in the palms & soles) Page 12 of 12