Skin Flashcards
What are the four main functions of the skin?
Protection against water/infection/UV
Detect sensory stimuli
Thermoregulation (e.g sweat)
Prevent dehydration
What are the three layers of the skin?
Epidermis, dermis and subcutis/hypodermis
Are there blood vessels in epidermis?
No
What sort of epithelium is epidermis?
Stratified squamous epithelium with keratinised upper layer
What are the layers of the epidermis?
Stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, stratum corneum.
How are cells of the stratum basale attached to the basement membrane?
Hemidesmosomes
What shape are the stratum basale ?
Cuboidal/columnar
What cells are in the stratum basale?
Stem cells and melanocytes
What happens to cells in the stratum basale?
Divide and differentiate to form keratinocytes
What cells are in the stratum spinosum?
Prickle cells (keratin producing)
What is highly expressed in the stratum spinosum
Keratin
What do desmosomes interact with
Keratin filaments
What do cells in the straum granulosum contain
Keratohyaline granules
What happens when stratum granulosum die?
Contents of granules and tonofilamnets form cross linked keratin under keratinocyte membrane
What is constantly happening to stratum corneum?
Shed and replaced by new keratinocytes from deeper layers which die forming keratin plates
What is the turnover from basal layer to desquamated keratin
25 days in feet (large impact) 45 days for back
In thick skin, which layer is thicker?
Stratum corneum
What do keratohyaline granules consist of ?
Specialised linking proteins that cross link each other and keratin tonofilaments, when cells die they release contents allowing cross linking with keratin filaments, cornified layer
What do keratinocytes become?
Corneocytes that make up the stratum corneum, after keratinoytes complete their differentiation programme, lose nucleus and cytoplasmic organelles.
What cell junctions are present?
Tight junctions in upper layers to maintain barrier. Desmosomes and hemidesmosomes for structural integrity.
What do melanocytes do in epidermis?
Synthesise melanin in granules (in basal layer)
What happens to melanin in granules in melanocytes?
Advance along cytoplasmic processes into cytoplasm of basal and prickle cell keratinocytes, melanin passed into other cell via projections
What causes albinism?
1) Tyrosinase catalyses formation of melanin in melanosome. Defects - albinism so non pigmented hair and skin.
2) May be deficincies of melanin granule transport (melanocytes are modified lysosomes so lysosomal protein trafficking abnornality)
What do Langerhan’s cells do?
Dendritic cell, present phagocytosed antigenic material to lymphocytes
Where are the langerhans cells found ?
All layers, especially the spinosum
Where are Merkel cells?
Stratum basale
What do Merkel cells do?
Sensory receptors in skin which synapse with peripheral nerve endings (can be grouped to form touch receptors)
What are nails?
Hard plates of keratinised epithelium (keratin filled squames in layers), specialised corneum.
Describe 2 skin appendages.
Pilosebaceous apparatus (i.e. hair folicle/shaft) Glands (eccrine and apocrine)
What is the embryological origin of eccrine and apocrine glands
Ectoderm
What are downgrowths of the epidermis?
Sweat glands and hair follicles (extend into the dermis)
What does the hair shaft grow from?
Hair bulb
What surrounds the hair shaft?
Hair follicle
What does the hair bulb consist of?
Contains rapidly dividing epithelial cells and melanocytes and surrounds dermal papilla
What muscle controls hair follicle and shaft?
Erector pilli muscles
Describe blood vessels supplying hair follicle
Hair follicle supplied by blood vessels in dermal papilla + nerve endings
Where are sebaceous glands found, what do they do?
Around follicle secrete sebum and moisturises hair. (holocrine secretion- cells diet and release contents)
Whereabouts in skin are eccrine glands found?
Subcutis or secretory part in dermis
What do eccrine glands do?
Secrete sweat for thermoregulation
Describe nerve supply of eccrine glands
Cholinergic symp control of secretion of sweat
Where are apocrine glands found?
Breasts, axillary, genital regions
Describe nerve supply of apocrine glands
Adrenergic sympathetic control
What is found in the dermis?
Blood vessels ,lymph, nerves ,epidermal appendages,
What are 2 layers of dermis?
Superficial loose papillary dermis
Dense reticular dermis
What is loose papillary dermis composed of?
Thin, loosely arranged collagen + elastin fibers with blood vessels and nerve endings
What are dense reticular dermis composed of?
Thicker, denser layers of collagen, elastic fibres and blood vessels
What are 2 plexues that supply skin, where are they found?
Cutaneous and subpapillary in dermis
Where does subpapillary plexus extend to?
Papillary dermis to form capillaries near BM of epidermis
What is subcutis layer made of?
Adipose tissue + network of vessels extending to form cutaneous plexus
What leads cells to differentiate in the epidermis?
A calcium gradient, with the lowest concentration in the stratum basale and increasing concentrations until the outer stratum granulosum, where it reaches its maximum. Calcium concentration in the stratum corneum is very high in part because those relatively dry cells are not able to dissolve the ions.
What is the most peripheral layer of living cells in the skin?
Stratum granulosum
What cells are not found in the corneum?
Fibrobasts
Non-ectodermal strucuture of the skin?
Erector pilli muscle (mesoderm)
A cell/structure that cycles through proliferative, regressive and quiescent stages?
Hair bulb
Where is melanin contained in melanocytes?
Their melanin is contained in melanosomes and premelanosomes
Describe cell junctions in stratum spinosum
Desmosomes, that appear as spiky membrane projections on histology.
