Dermatology - Development and Structure of Epidermis Flashcards
2 main layers of skin and tissue types of both?
Epidermis (outer layer) - stratified cellular epithelium
Dermis (beneath epidermis) - connective tissue
Formation of the epidermis layers?
Ectoderm cells form a single layer periderm (replaces the epidermis); the layers of cells are increased until periderm cells are cast off
Formation of the dermis layers?
Formed from mesoderm below ectoderm
Melanocytes and their formation?
Pigment-producing cells from neural crest
Gastrulation and period of time during which it occurs?
Cellular organisation into germ layers takes place during days 7-10
Foetal skin layers at 4 weeks?
From superficial to deep:
Periderm
Basal layer
Dermis
Foetal skin layers at 16 weeks?
Keratin layer Granular layer Prickle cell layer Basal cell layer Dermis
Foetal skin development at 26 weeks?
Hair follicles have formed, along with arector pili muscles and sebaceous glands; hairs extend through the epidermis
What is the dermo-epidermal junction
Interface between the dermis and epidermis
Cells of the epidermis?
95% of the epidermis consists of keratinocytes; the rest are stratified squamous epithelial cells, Merkel cells, Langerhan cells and melanocytes
Describe the epidermal variation at different body sites
On the soles of the feet, there is no hair, as opposed to the armpit and scalp; also, in some regions, there are more sweat glands
Dermatological conditions where there is a loss of regulation of epidermal turnover?
Skin cancer
Psoriasis
Process of differentiation of keratinocytes?
Migrate from the basement membrane, over 28 days from the bottom to the top, to continuously regenerate the epidermis
Structure of the basal cell layer?
One cell thick (small and cuboidal); there are many intermediate filaments/keratin The basal cell layer is curved to supply rigidity
Structure of prickle cell layer?
Consists of larger polyhedral cells and many desmosomes, which are connected to intermediate filaments
Structure of the granular layer?
2-3 layers of flatter cells along with: Large keratohyalin granules (contain proteins) LAMELLAR BODIES (Odland bodies)
Features of the granular layer?
Cell nuclei are lost and the layer has a high lipid content
What is the cornified envelope?
Cornified envelope replaces the plasma membrane of differentiating keratinocytes and consists of keratins that are enclosed within an insoluble amalgam of proteins and a lipid envelope
This originates in the granular layer
Structure of the keratin layer?
Mostly consists of keratin and fillagrin (links keratin to epithelial cells) but also corneocytes (overlapping non-nucleated cell remnants)
This layer forms a waterproof barrier
What happens when the keratin layer thickens?
A transparent layer becomes less so, e.g: thickened nails and white patches on mucosal surface of mouth, and the skin can thicken
