Anatomy Of Epidermis Flashcards
What kind of epithelium is the epidermis?
Stratified squamous
What are the layers of the epidermis?
- Stratum corneum
- Stratum lucidum (only palms and soles)
- Stratum granulosum
- Stratum spinosum
- Stratum basale (basal cell layer)
What is the stratum corneum?
An outer layer of dead cells and keratin
What is the purpose of the stratum corneum?
Presents barrier to bacterial and environmental toxins
How does the skin epithelium change as the cells migrate to the skin surface?
It becomes super specialised, forming a squamous shape
How does the skin epithelium form a squamous shape is it migrates to the surface?
- Filling cytoplasm with proteins, especially keratin
- Cross-linking polymer fibres into strong stable networks
What is the purpose of the squamous shape of the skin epithelium?
It means the skin is resistant to mechanical trauma, and allows shedding without disruption of the whole surface
What are the epidermal cells of the skin known as?
Keratinocytes
What holds together the keratinocytes?
Organelles called desmosomes
What are desmosomes?
Cell adhesion structures
Where are desmosomes especially prominent?
In the epidermis and mucous membranes
What is the source of new skin epidermal cells?
The basal cell layer
What is the role of rete pegs in the skin?
Ensures attachment of the dermis to the epidermis via the basement membrane
What are the major cell types forming the epidermis?
- Keratinocytes
- Melanocytes
- Merkel cells
- Langerhans cells
What is the function of keratinocytes?
Produce keratin and lipids as a protective barrier
What happens to daughter cells of keratinocytes?
They move to the surface to form the cornified layer (stratum corneum)
What is the function of melanocytes?
Produce melanin
What is the function of melanin?
- Give pigment to skin
- Protects cell nuclei from UV radiation induced DNA damage
What happens to melanin production following UV-induced cell damage?
It is increased
How is melanin production increased after UV-induced cell damage?
UV-induced DNA damage and/or its repeat produce initiating signals that induce an increase in melanogenesis
Where does melanogenesis occur?
Specific ovoid organelles called melanosomes
Where are melanosomes produced?
In dendritic melanocytes
What is each melanocyte associated with?
Around 36 keratinocytes and one Langerhans cell
What is the unit of 1 melanocyte, keratinocytes, and 1 Langerhans cell called?
Epidermal melanin unit
What happens to melanin synthesised within melanosomes?
It is transported via dendrites to adjacent keratinocytes
What happens to the melanin once it has been transported to keratinocyters?
It accumulates within keratinocytes and melanocytes in the perinuclear areas
How does melanin protect against UV damage?
It serves as a physical barrier that scatters UV radiation, and reduces its penetration through the epidermis
What is the function of Merkel cells?
They contain specialised nerve endings for cutaneous sensation
What is the function of Langerhans cells?
They present antigens and active T-lymphocytes for immune protection
What is meant by the epidermal turnover time?
The time taken for migration of cells from stratum basale to stratum corneum
What is the epidermal turnover time?
Approx 30 days
