Skin Structure/Function Flashcards by Brendan Lewis

What are the protective functions of the skin?

protects against:
mechanical impact
pressure
temperature variations
microbes
radiation/chemicals

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how does the skin physiologically regulate the body?

body temperature - sweat/hair
peripheral circulation changes
fluid balance - sweat (minor)
vitamin D synthesis

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how does the skin provide sensation?

through a nerve cell network that detects and relays changes in the environment (temperature, touch, pain)

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describe the characteristics of the stratum corneum

large, flat, plate-like envelopes filled with cross-linked keratin
contains lipids
no nucleus/cytoplasm

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describe the characteristics of the stratum granulosum

flattened cells, contains keratohyalin granules
beginning to lose nucleus and cytoplasm

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describe the characteristics of the stratum spinosum

polyhedral keratinocytes
rich in desmosomes

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describe the characteristics of the stratum basale

cuboidal/low columnar cells
mitotically active, constant regen of other layers
connected to BM by hemidesmosomes

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what additional layer does thick skin have?

stratum lucidum

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what features does the dermis contain?

CT - collagen type 1 (tensile strength), elastin (allows stretch) and ground substance
fibroblasts
blood supply

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what are the 2 dermis layers called?

papillary (upper)
reticular (lower)

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describe the function of the dermo-epidermal junction

attachment of epidermis and dermis
aligns epidermal cells
serves as reepithelialisation base in wound healing
barrier function (to/from epidermis)

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what are the functions of the subcutis?

energy source
shock absorption
insulation

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explain the structures in the papillary dermis allowing skin to perform its sensory function

merkel cells - attaches to PD and acts as mechanoreceptors
meissners corpuscles - mechanoreceptors responsible for touch in PD in hands/feet

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what structure in the subcutis allows skin to perform its sensory function?

pactinian corpuscles - detects deep pressure/vibration

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explain the function of eccrine glands in skin

temp control glands that excrete sweat
mostly found in palms, soles and axillae

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what are apocrine glands and where are they found?

scent glands found in axillae and genitals

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what is the function of sebaceous glands and where are they found?

formed from hair follicle
present everywhere except palms and soles
produces sebum

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what is the definition of epithelium?

type of tissue that covers body surfaces, lines cavities or forms glands

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what type of epithelium is the epidermis?

stratified squamous keratinised epithelium

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where are keratinocytes located and what is their function?

location - keratinised stratified squamous epithelium
function - protection/barrier and vitamin D production

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where are stem cells found in the epidermis and what is their function?

location - stratum basale
function - self renewal/repopulation of epidermal layers

where are merkel cells located and what is their function?

located - basal layer of epidermis
function - sensation

where are langerhans cells located and what is their function?

located - stratum spinosum and papillary dermis
function - dendritic cell: antigen presentation and phagocytosis

where are melanocytes found and what is their function?

location - basal layer
function - radiaton protection

what can chronic UV exposure in humans lead to?

loss of skin elasticity/fragility abnormal pigmentation blood vessel haemorrhage wrinkles/premature ageing

what is keratins location and function?

location - all epidermal layers function - structural proteins, intermediate filaments

what is profilaggrin's location and function?

location - keratohyalin granules function - converted to filaggrin which fuses keratin filaments into tight bundles

what is involucrin's location and function?

location - keratohyalin granules function - forms cell envelope around stratum corneum cells and cross links to loricrin (also in keratohyalin granules)

what are polysaccharides/glycoproteins/lipids location in the skin and what is their function?

location - lamellar granules function - extrudes into intercellular space and forms the 'cement' holding stratum corneum cells together

what is the function of dermal fibroblasts?

collagen/elastin/ECM synthesis acts as growth factors

what is the function of dermal lymphocytes?

immunosurveillance

what is the function of dermal dendritic cells?

phagocytosis and antigen presentation

what is the function of dermal mast cells?

produces inflammatory mediators (e.g histamine) during degranulation produces chemotactic factors for eosinophils and neutrophils

what main molecules are present in the dermis and what are their functions?

type 1 collagen - structural fibrous proteins elastin - elasticity and recoil proteoglycans/glycosaminoglycans - hydration

what is the definition of a wound?

breakdown in the protective function of the skin

desrcibe the cellular features of a wound

loss of epithelium continuity possible loss of underlying CT

what is damaged in an erosion wound?

only epidermis

what is damaged in an ulceration wound?

structures deep to epidermis

what is damaged in a partial thickness wound?

epidermis + some dermis

what is damaged in a full thickness wound?

epidermis, dermis and deeper structures

what are the 3 aspects of wound healing?

inflammatory, proliferative, remodelling

explain the process of the inflammation/vascular phase in wound healing

platelets initiate haemostasis/blood clot and initiate the healing cascade neutrophils/macrophages recruited to fight infection by phagocytosing dead tissue and microbes

explain the process of reepithelialisation in proliferative wound healing

epithelial cells loosen cell-cell adhesions and migrate to wound site, cover the granulation tissue and meet in the middle once one layer of keratinocytes covers the area, all keratinocytes proliferate

what forms the granulation tissue in proliferative wound healing?

type 3 collagen

what is neurovascularisation in proliferative wound healing?

proliferation and migration of endothelial cells

what physiological changes occur in the remodelling phase of wound healing?

granulation tissue becomes mature scar tissue collagen organised into thick bundles and cross-linked, forming a mature scar type 3 collagen becomes type 1

what growth factor is responsible for reepithelialisation?

epidermal growth factor (EGF)

what is the function of platelet-derived growth factor (PDGF)?

matrix formation (increased fibroblast abundance/activity) and remodelling (protease production)

what is the function of vascular endothelial growth factor (VEGF)?

angiogenesis (endothelial cell proliferation/migration)

what signalling molecules are responsible for inflammation in wounds?

interleukin 1 (Il-1), Il-6 and tumour necrosis factor a (TNFa)

what local factors influence wound healing?

infection, foreign body, oxygenation, vascular supply

what systemic factors influence wound healing?

age, disease, alcohol/smoking, immonucompromised conditions, obesity, medications