DSF Histo of Skin Flashcards
3 layers of skin
Epidermis
Dermis
Hypodermis (subcutis)
Epidermis
Keratinized stratified squamous epithelium
Dermis
Papillary and Reticular
Loose irregular and dense irregular CT
Hypodermis (subcutis)
Loose CT
Shock absorption, insulation, energy reservoir
Thick skin
Soles and palms Thick layer of epidermis Only eccrine glands, no other appendages Highly innervated for exquisite sensory discrimination *Have Stratum lucidum
4 cell layers of epidermis (5 in thick skin)
Stratum basale Stratum spinosum Stratum granulosum Stratum lucidum Stratum corneum
4 cell types w/in the epidermal cell layers
Keratinocytes
Melanocytes
Langerhans cells
Merkel cells
Keratinocytes
Ectodermally-derived cells
Protection from mechanical forces, UV light, water barrier
Specialized apoptosis involved in maturation
Contain majority of skin’s melanin
Melanocytes
Produce melanin (oxidation of Tyr (tyrosinase key), released in melanosomes)
Found in stratum basale
Origin: neural crest
Langerhans cells
Stratum spinosum
Immune cells of epithelium - can migrate
Lymphocytes, mast cells, macrophages
Dendritic cells (APCs) - adaptive immunity
Derived from bone marrow stem cells (mesoderm)
NO pigment or keratin, can be identified in TEM by folded nuclei
Birbeck granules
Merkel cells
Mechanoreceptor cells of epithelium (SB of epidermis)
Also found along basement membrane of hair follicles
Form Merkel corpuscle along w/ underlying nerve processes
Likely neural crest origin
Intimately associated w/ a nerve fiber
Stratum basale
Single cuboidal/low columnar layer, attached to BL by hemidesmosomes
Proliferative
Beginning of keratin synthesis - few keratin filaments
Continuous w/ basal layer of appendages
Stains blue due to lots of free ribosomes
Vitamin D production
Melanin present above nucleus (to protect DNA)
Stratum spinosum
Stratified and non-uniform
Vitamin D production
“Spinous” processes: cytoplasmic projections/desmosomal attachments
Near basal layer: Proliferative capability, keratin synthesis
Near surface: flatter, larger, more TFs, start of water barrier formation
Keratohyalin granules
Stratum granulosum
Contain filaggrin and trichohyalin - involved in aggregation of keratin filaments into tonofibrils (TFs)
Stratum granulosum
1-3 layers thick No proliferation Even more keratin filaments bundled into TFs Lamellar bodies released Keratohyalin granules Cells undergo apoptosis
Stratum corneum
Dead cells (no nuclei/organelles) Keratin matrix Coated w/ water barrier Subject to exfoliation/desquamation *SL in thick skin similar
Psoriasis
Accelerated cell proliferation and maturation rate
Characteristic scaly plaques
Desquamation of SC
Deep layer of SC at neutral pH, becomes acidic superficially - disrupts desmosomal junctions
Cytocrine secretion
Process by which keratinocytes take up melanin: phagocytose tips of melanocyte dendritic processes
Direct transfer of secretory material from 1 cell to another
What is skin pigmentation determined by?
Amount, type, and packaging of melanin in epidermis
Partially controlled by melanin breakdown rate (faster in lighter skinned individuals)
(not determined by # of melanocytes)
Albinism
Hypopigmentation
Defective melanin production
Lack of melanin, due to defect in tyrosinase
Normal # of melanocytes
Vitiligo
Hypopigmentation
Autoimmune destruction of melanocytes
Dermal-Epidermal Junction
Epidermis separated from dermis by BL
Rete ridges: epidermis extends down
Dermal papillae: dermis extends up
Gives fingerprint (high density)
Bulbous pemphigous
Autoimmune disorder w/ antibodies against the hemidesmosomes
Huge blisters occur due to disruption of dermal-epidermal junction
Papillary Dermis
Superficial loose (areolar) cellular layer/CT
Reticular Dermis
Lower, denser, less cellular layer/CT
Eccrine (sweat) gland
Thermoregulation, can be stimulated by stress
Secrete hypotonic fluid that evaporates on skin surface
Found in dermis and superficial hypodermis
Ectodermal in origin
Simple, coiled tubular glands
Glands are pseudostratified epithelium but ducts are 2 layer stratified cuboidal
Merocrine secretion - exocytosis
Controlled by sympathetic NS
Clear, Dark, Myoepithelial cells
Apocrine (sweat) gland
Secrete fatty acids, proteins, carbs, ammonia, serous fluid, pheromones by budding off of the cytoplasm
Found in axilla, areola, genital region and anus
Ducts discharge into the hair follicle
Found in dermis and upper hypodermis
Merocrine gland - coiled tubular, occasionally branched
Simple cuboidal epithelium
Highly androgen sensitive; not functional until puberty
Underarm odor
Bacteria process apocrine secretions
Sebaceous gland
Produce and secrete sebum: highly lipid secretion that lubricates the skin
Resist friction and water barrier
Holocrine gland: secretions made up of disintegrated cells and sebum (apoptosis)
Sebocytes form acini which attach to a common duct
Highly androgen sensitive
Hair follicles
Hair follicle continuous w/ epidermis (SB)
Sebum deposition moisturizes hair
Hair growth occurs at the bulb, where blood supply and innervation richest
Matrix cells in bulb proliferative
Merkel cells
Melanocytes that contribute to hair color
Associated w/ arrector pili muscle
Meissner Corpuscles
Encapsulated mechanoreceptors found in dermal papillae
Multiple flattened Schwann cells interspersed by spiraling nerve fibers giving a whorled appearance
Tactile, fine light touch sense
Free nerve endings
Simple unmyelinated nerves found penetrating the epidermis
Pacinian Corpuscles
Deep dermis and hypodermis
Sense pressure and vibration
Huge, look like onions in LM
Peritrichial nerves
Hair base and shaft highly innervated and stimulated by movement of hair
Ruffini end organs
Stretch receptor found in dermis and joint capsules
Encapsulated fluid-filled structures traversed by collagen
Transmit kinesthetic info (position sense, movement, etc.)
Diabetic neuropathy
Peripheral nerve damage leads to loss of skin sensation - can make patient unaware of minor injuries
Severe infections can occur if injury goes unnoticed
Blood Supply to skin
Blood reaches skin via larger vessels in hypodermis (highly vascularized) Subpapillary Plexus (gives off capillary loops) and Cutaneous Plexus
Arteriovenous anastomoses
Shunts in upper dermis
Highly involved in thermoregulation and preservation (shock)
In cold and when intravascular volume low (shock): blood shunted away from skin
Protective Features of Skin
Mechanical: Stratified squamous epithelium, keratinization, water barrier
Immunoprotection: LC, diffuse lymphatic tissue, dermal lymphatics, macrophages
UV damage: melanin
Follicular bulge
(Of hair follicle)
Has stem cells for melanocytes and for epidermis
