SM_255a: Structure and Function of Skin Flashcards
Skin functions include ____, ____, ____, ____, ____, and ____
Skin functions include barrier, repair, immunologic, sensation, thermoregulation, and appearance
- Barrier: resist mechanical stress, limit water loss from inside, block entry from outside, UV shield
- Repair: wound healing
- Immunologic: temper and alert immune system
- Sensation: pain, itch, pressure
- Thermoregulation, insulation, and absurption
- Appearance: quality of life
Skin layers from outermost to innermost are ____, ____, and ____ and appendages include ____, ____, ____, and ____
Skin layers from outermost to innermost are epidermis, dermis, and hypodermis and appendages include hair, sebaceous glands, sweat glands, and nails
Epidermis is ____
Epidermis is keratinizing stratified squamous epithelium
Dermis is ____
Dermis is connective tissue/stroma
Dermis includes the ____ and ____
Dermis includes the outer papillary dermis and inner reticular dermis
Epidermis is ____, while the dermis ____
Epidermis is avascular, while the dermis is vascular
Describe the layers of the epidermis from bottom up
Layers of the epidermis from bottom up
- Basal layer (stratum basale): proliferation/anchorage - E-cadherin
- Spinous layer (stratum spinosum): adhesion - demososomes
- Granular layer (stratum granulosum): differentiation
- Cornified layer (stratum corneum): death
Epidermal cell layers are ____
Epidermal cell layers are morphologically distinct
____ are the major cell type in the epidermis
Keratinocytes are the major cell type in the epidermis
(keratinocytes exist in various states of proliferation and differentiation in epidermis)
In addition to keratinocytes, ____, ____, and ____ are found in the epidermis
In addition to keratinocytes, Langerhans cells, melanocytes, and Merkel cells are found in the epidermis
- Langerhans cells: dendritic antigen presenting cells
- Melanocyte: pigment-producing cells
- Merkel cells: mechanoreceptor
Epidermis functions primarily to build a ____ in order to ____, ____, ____, and ____
Epidermis functions primarily to build a semi-permeable barrier in order to resist physical trauma and repair wounds, prevent entry of noxious agents (outside-in barrier), limit excessive water loss (inside-out barrier), and protect against UV irradiation from sun
Epidermis building involves replenishing to ____
Epidermis building involves replenishing to maintain a constant supply of keratinocytes to repopulate upper layers
- Stem cells in the basal layer give rise to proliferating compartment
- Basal layer cells exit cell cycle and replenish upper layer
- Outermost cells are constantly sloughed off
- Epidermis turns over every 30 days
Psoriasis is an ____ skin disease that involves ____, ____, and ____
Psoriasis is an inflammatory skin disease that involves increased keratinocyte proliferation and turnover, abnormal differentiation, and formation of thick scaly plaques
Epidermis building involves resisting which is accomplished by ____
Epidermis building involves resisting which is accomplished by specialized structures to yield a strong cell
- Keratinocytes maintain shape by building cytoskeleton networks: microtubules, actin-based microfilaments, keratin-based intermediate filaments
- 54 different human keratins pair up to form intermediate filaments
- Keratins are major protein in keratinocytes
- Keratin composition changes as keratinocytes differentiate
____ are responsible for maintaining shape of the epidermis by building cytoskeleton networks
Keratinocytes are responsible for maintaining shape of the epidermis by building cytoskeleton networks
Keratins ___ and ___ are expressed in the basal layer, while keratins ___ and ___ are expressed in the spinous and granular layers
Keratins 5 and 14 are expressed in the basal layer, while keratins 1 and 10 are expressed in the spinous and granular layers
____ occurs due to issues with keratin 5 and 14 in the basal layer
Epidermolysis bullosa simplex occurs due to issues with keratin 5 and 14 in the basal layer
____ occurs due to issues with keratin 1 and 10 in the spinous and granular layers
Epidermolytic ichthyosis occurs due to issues with keratin 1 and 10 in the spinous and granular layers
____ anchored to the ____ attach the epidermis to the underlying dermis
Keratinocytes anchored to the underlying dermis attach the epidermis to the underlying dermis
____ are integrin-based junctions that connect basal keratinocytes to the basement membrane
Hemidesmosomes are integrin-based junctions that connect basal keratinocytes to the basement membrane
____ occurs due to mutations in hemidesmosome gene COL17A1
Junctional epidermolysis bullosa occurs due to mutations in hemidesmosome gene COL17A1
____ occurs due to autoantibodies against collagen 17, which ____
Bullous pemphigoid occurs due to autoantibodies against collagen 17, which breaks the connection between basal keratinocytes and basement membrane
____ are specialized junctions that anchor keratin to sites of cell-cell contact
Desmosomes are specialized junctions that anchor keratin to sites of cell-cell contact
____ occurs when autoantibodies target proteins found in desmosomes, ____
Pemphigus vulgaris occurs when autoantibodies target proteins found in desmosomes, breaking the connection between adjacent keratinocytes
____ made of ____ allow for selective permeability in the epidermis
Tight junctions made of occludin allow for selective permeability in the epidermis
Stratum corneum can be likened to ____
Stratum corneum can be likened to bricks and mortar
- Bricks -> corneocytes: anucleate, keratin-filled, dead keratinocytes encased in a highly crosslinked specialized membrane - the cornified envelope
- Mortar -> lamellar membrane: lipids (ceramides, cholesterol, and free fatty acids) extruded from keratinocytes to form a hydrophobic seal
____ is caused by defects in lipid transport in the epidermis
Harlequin ichthyosis is caused by defects in lipid transport in the epidermis
(mutation in ABCA12 gene)
____ is caused by defects in cornified envelope production
Lamellar ichthyosis is caused by defects in cornified envelope production
(mutation in TGM1 gene)
Strategies for building for a barrier include ____, ____, ____, and ____
Strategies for building for a barrier include replenish, resist, repel, and reside
- Replenish: maintain a constant supply of keratinocytes to repopulate upper layers
- Resist: adopt specialized structures to yield a strong sticky cell
- Repel: form an impermeable seal (fence and gate barrier), extrude lipids and cornified envelope
- Reside: exist in a space that provides tough flexible support and nutrient/gas exchange
Dermis makes up the bulk of the skin and is designed for maintaining ____ and ____
Dermis makes up the bulk of the skin and is designed for maintaining pliability and tensile strength
___ secrete connective tissue proteins to build a strong but flexible matrix, which is composed of ____, ____, and ____
Fibroblasts secrete connective tissue proteins to build a strong but flexible matrix, which is composed of collagen fibers, elastic fibers, and ground substance
- Collagen fibers: tensile strength
- Elastic fibers: stretch and recoil
- Ground substance: glue - glycosaminoglycans (hyaluronic acid), produced and degraded by fibroblasts and mast cells, binds water
____ are a key component of basement membrane zone
Collagens (Type IV, VII) are a key component of basement membrane zone
(mutations in COL7A1 causes dystrophic epidermolysis bullosa - slight touch causes loss of anchorage of epidermis to dermis)
____ make the skin pliable
Elastic fibers make the skin pliable
(mutations in genes producing elastin precursors cause cutis laxa)
Apart from fibroblasts, ___, ___, ___, and ___ are found in the dermis
Apart from fibroblasts, dermal papilla cells, mast cells, monocytes / macrophages, and lymphocytes are found in the dermis
- Dermal papilla cells: specialized fibroblasts (hair growth cycle)
- Mast cells (heparin and histamine release): immediate hypersensitivity - urticaria (hives)
- Monocytes / macrophages: phagocytic (wound healing, debris clearance)
- Lymphocytes: immunoregulatory (inflammatory skin diseases)
Inflammatory cells primarily reside in the ____ but also impact epidermal homeostasis in diseases like ____
Inflammatory cells primarily reside in the dermis but also impact epidermal homeostasis in diseases like psoriasis
Hairs are of ____ origin and associated with ____ and ____
Hairs are of epithelial origin and associated with arrector pilorum muscles and sebaceous glands
Sebaceous glands contain ____ that secrete ____ into the duct
Sebaceous glands contain sebocytes that secrete their entire cell contents (holocrine secretion) into the duct
Sweat apparatus contains ____ and ____ glands
Sweat apparatus contains apocrine and eccrine glands
Summarize the major learning points about skin structure and function
Major learning points about skin structure and function
