Intro to Dermatology- Skin Flashcards
What are the different layers of the skin?
Epidermis- arises from ectoderm
Basement membrane - dermal-epidermal junction
Dermis- arises from mesoderm
Subcutaneous fat
How is skin formed?
Week 4: epidermis is formed as a single layer of cuboidal cells
Week 5: secondary layer of squamous, non-keratinising cuboidal cells develops. Develops white waxy substance called vernix caseosa
Week 11: Basal layer of cuboidal cells (stratum germinativum) proliferates to form multi-layered intermediate zone- four more specific strata form (stratum spinosum, corneum, granulosum and lucidum)
Week 9-12: development of hair follicles in stratum germinativum and appearance of lanugo hair
What are melanocytes developed from and where do they migrate to?
Developed from the neural crest- melanoblasts
They migrate dorsally between week 6-8 to develop in epidermis and hair follicles
By week 12-13 most melanoblasts have reached destination and become melanocytes
A subset of melanoblasts form melanocyte stem cells in hair follicle bulge that replenish differentiated melanocytes
How are melanocytes regulated?
Melanocortin 1 receptor (MC1R), a G protein coupled receptor regulates quantity and quality of melanins produced:
- Its controlled by agonist alpha-melanocyte-stimulating hormone (aMSH) and adrenocorticotrophin hormone (ACTH) and antagonist agouti signalling protein (ASP)
- Activation of MC1R by agonist leads to melanogenic cascade and the synthesis of eumelanin
- ASP reverses these effects and elicits production of pheomelanin
- ACTH can also up regulate expression of MC1R gene
What is the effect of UV exposure to melanin?
It causes:
- increased expression of MITF and downstream melanogenic proteins inc. Pmel17, MART-1, TYR, TRP1 and DCT- increases melanin content
- Increases PAR2 in keratinocytes which leads to increased uptake and distribution of melanosomes by keratinocytes
What are the different layers of the epidermis?
Composed of keratinocytes Stratum Lucidum (palms and soles only) Stratum Corneum (no nuclei or organelles) Stratum Granulosum Stratum spinousum Basal layer
How are cells replaced in skin?
Cell division occurs in the basal layer
Cells move from the basal layer upwards towards the surface. This takes about 30 days (Accelerated in skin diseases)
How are keratinocytes structured?
Filamentous cytoskeleton includes:
- Actin- containing microfilaments
- Tubulin containing microtubules
- Intermediate filaments (keratins)
What is the role of keratins?
Structural properties Cell signalling Stress response Apoptosis Wound healing
How are keratinocytes renewed?
Keratinocytes in stratum corneum are dead and regularly removed and replaced by cells from deeper layers
What are desmosomes?
Major adhesion complex in epidermis
Anchor keratin intermediate filaments to cell membrane and bridge adjacent keratinocytes
Allow cells to withstand trauma
What are gap junctions?
Clusters of intracellular channels (connexons)
Directly form connections between cytoplasm of adjacent keratinocytes
Essential for cell synchronisation, cell differentiation, cell growth and metabolic coordination
What are adherent junctions?
Transmembrane structure
Engage with actin skeleton
What are tight junctions?
Role in barrier integrity and cell polarity
What other cells can be found in the epidermis?
Melanocytes: Dendritic. Distribute melanin pigment to keratinocytes. No. of melanocytes is the same in all skin types
Langerhans cells: Dendritic. Antigen presenting cell
Merkel cells: mechanosensory receptors
Mast cells
What makes up the basement membrane?
Aka. dermal-epidermal junction
Has proteins and glycoproteins: collagen (V, VII), laminin, integrins
What is the role of the basement membrane?
Cell adhesion
Cell migration
What are the 2 different layers of the dermis?
Papillary dermis: superficial and has loose connective tissue and is vascular
Reticula dermis: deep and has deep connective tissue and forms bulk of dermis
What makes up the dermis?
Protein: collagen (mainly I and III), elastic fibres (fibrillin, elastin)
Glycoproteins: fibronectin, fibrin, integrins- facilitate cell adhesion and cell motility
Ground substance: between dermal collagen and elastic tissue (glycosaminoglycan and proteoglycan)
Cells: mainly fibroblasts but also histocytes, mast cells, neutrophils, lymphocytes, dermal dendritic cells
What gives blood supply to the skin?
Deep and superficial vascular plexus- doesn’t cross into epidermis
What supplies innervation to the skin?
Sensory
Autonomic:
-Cholinergic- eccrine (swear found all over body)
-Adrenergic- eccrine and apocrine (body odour sweat)
Afferent nerve receptors:
-Corpuscular- encapsulated receptors (dermis)
-Free- non-encapsulated receptors (epidermis)
What is the pilosebaceous unit?
Follicle, hair shaft, sebaceous gland, pili arrector muscle
What are the different receptors found in the skin?
Meissner’s corpuscle
Ruffini corpuscle
Pacinian corpuscle
Merkel cell
What is a meissner’s corpuscle?
Aka. Tactile corpuscle
Encapsulated, unmyelinated mechanoreceptors
Lamellated capsule
Found in superficial dermis
Most concentrated in thick, hairless skin (finger pads, lips)
Detect light touch and slow vibration
Senses low frequency stimulation at levels of dermal papilla
