Dermatology Flashcards
Where does the epidermis originate from?
Ectoderm
Where does the dermis arise from?
Dermis
When does the epidermis form?
Week 4
What happens during the first stage of skin development?
Epidermis forms by week 4- single basal layer of cuboidal cells- superior of mesoderm layer
Which cells form the basal layer during initial stages of skin development?
Cuboidal cells
When does the second stage of skin development occur?
Week 5
What types of cells form the periderm?
Squamous non-keratinising cuboidal cells, generates white waxy protective substance - vernix caseosa
What is the white waxy protective substance that forms the periderm?
Vernix caseosa
Which is the deepest epidermal layer?
Straum germinativum
Stratum basale
Which layers of epidermis forms deep to superficial? (Stage 3)
Straum Spinosum
Stratum Granulosum
Stratum Lucidum (palms and soles)
Stratum Corneum
What do epidermal ridges form?
Dermal papillae
At which weeks do lanugo hair and hair follicles in stratum germinativum form?
Weeks 9-13
How do melanocytes interact with keratinocytes?
Dendritic interactions
What is the principal function of melanocytes?
Responsible for melanin secretion through melanogenesis
Which cells do melanocytes arise from?
neural crest
What term is used to describe progenitor melanocytes?
Melanoblasts
Where do melanocyte stem cells reside?
Hair follicle bulge
Which receptor regulates the quantity of melanin secretion?
Melanocortin 1 receptor (MC1R)- G protein coupled receptor
Which agonist mediates melanogenesis via MC1R?
Alpha-melanocyte stimulating hormone (Alpha-MSH)
What is the rate limiting enzyme in melanogenesis?
Tyrosinase
Which molecule forms the precursor of melanin?
Eumelanin
Which gene increases expression of POMC?
p53
What effect does increased exposure to UV radiation have?
keratinocyte receives increased exposure to UV radiation, DNA damage induces mutation.
Stimulates tumour suppressor gene, p53 –> increases expression of POMC, precursor or alpha-MSH, this increases expression of enzymes and proteins required for synthesis of melanin and melanocytes
Which transcription factors is increases melanogenesis?
MITF
Which downstream melanogenic proteins increase melanin content?
Pmel17, MART-1, TYR, TRP1
DCT
Which melagenic proteins play a role in melanosomes?
MART-1
MPL-1
Increased expression of _____ in keratinocytes increases uptake & distribution of melanosomes by keratinocytes:
PAR-2
How are melanosomes transferred into keratinocytes?
Pseudopodia of melanocyte interlock with keratinocytes, enabling transfer of melanosome; internally degranulates & releases melanin
Which protein reverses effects & elicits production of phenomelanin?
Agouti signalling protein (ASP)
Which hormone up regulates MCIR expression?
ACTH
Which type of epithelial cells form the epidermis?
Composed of keratinised, stratified squamous epithelium
Is the epidermis avascular or vascular?
Avascular
What are the layers (deep to superficial) of the epidermis?
Stratum Basale
Stratum Spinosum
Stratum Granulosum
Stratum Corneum
Which epidermal layer is found exclusively in palms and soles?
Lucidum
Which epidermal layers are keratinocytes located within?
All layers besides stratum basal
Which molecule is stored & synthesised within keratinocytes?
Keratin
What is the function of keratin?
Intracellular fibrous protein that provides strength and water resistance
How are keratinocytes replaced in the stratum corneum?
Replaced by cells from deeper layers
What is the function of the stratum basale?
Attaches epidermis to the basal lamina cells bound to dermis
Basal cells precursors to keratinocytes
Melanocytes produce melanin
Merkel cells
Which structure located on the superficial dermis increases the strength of connection between the epidermis & dermis?
Dermal papilla
Which cells are precursors to keratinocytes?
Basal cells
What is the fate of mitotically produced keratinocytes?
Superficially accumulate away from the stratum basal
What is the function of Merkel cells?
Functions as receptor, responsible for stimulating sensory touch fibres
Where are Merkel cells located?
Stratum Basle
Which epidermal layer contains melanocytes?
Stratum Basale
How are cells connected within the stratum spinosum?
Via desmosomes
What are desmosomes?
Adhesion protein complexes present in the epidermis
Function:Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocyte, enables cells to withstand trauma
Where are Langerhans cells located?
Express macrophage function
Why are the cell membranes within the stratum granulosum thick?
Due to keratin presence, and keratohyalin
What granules accumulate within the stratum granulosum?
Lamellar granules,
In which epidermal layer, does the nuclei and cell organelles disintegrate?
Stratum granulosum
What is the most superficial layer of the epidermis?
Stratum corneum
What is the function of the stratum corneum?
Keratininsation of cells prevents penetration of microbes, and the dehydration of underlying tissues.
Provides a mechanical protection against abrasion
How is the dermis separated from the epidermis?
Laye of connective tissue and subcutaneous fat, deep to epidermis, and separated by basement membrane
What is the structure of keratinocytes?
Filamentous cytoskeletons comprise of actin-containinng microfilaments
Tubulin-containing microtubules and intermediate filaments (Keratins)
What are the 5 roles of keratins?
Structural properties Cell signalling Stress response apoptosis wound healing
Connexons are _____ junctions?
Gap junctions
What is the role performed by connexon gap junctions?
Clusters of intercellular channels, directly form connections between cytoplasm of adjacent keratinocytes
What types of junctions are transmembrane structures which engage with actin skeletons?
Adherens junctions
Which type of junctions play a role in barrier integrity and cell polarity?
Tight junctions
Which cells are menlanocytes intimately associated with?
Keratinocytes
How is melanin distributed into keratinocytes?
Formation of a epidermal melanocyte unit, synthesised by melanocytes and disturbed into melanosomes into keratinocyte
What function is performed by Langerhans cells?
Reside within the epidermis as immune sentinels
Cells determine appropriate adaptive immune response (inflammation or tolerance) by interpreting microenvironmental context
Functionally, Langerhans cells express antigen presenting properties; behaving as dendritic cells
Where are Merkel cells located?
Within the basal layer of the epidermis
What is the function of Merkel cells?
Exhibit mechanosensory receptor properties that mediate sense of touch and follicle movement
Which inflammatory host cells reside within the epidermis?
Mast cells
Which Ig mediated reactions?
IgE-mediated reactions through FceRI receptors upon activation
Which main inflammatory cytokine is released from mast cells?
Histamines
The basement membrane is considered to be the ______ junction:
Dermal-epidermal
What comprises the basement epidermal-dermal junction?
Glycoproteins and proteoglycans
Collagen (IV, VII, laminin, integrins)
What is the function of the basement membrane?
Cell adhesion and cell migration
Which cells predominantly produce collagen?
Fibroblasts
Which molecules are found within the dermis?
Compose of interconnected mesh of elastin and collagenous fibres
What is the most superficial layer of the dermis?
Papillary layer
Which epidermal layer does the papillary layer project into?
Stratum basal of the epidermis, projection as dermal papillae
What projections are formed via the papillary layer into the epidermal stratum basale?
Dermal papillae
What type of connective tissue forms the dermis?
Loose areolar connective tissue.
Which two main types of cells reside within the papillary layer?
Adipocytes and fibroblasts
Which touch receptors are located within the papillary layer of the dermis?
Meissner corpuscles