Histology Flashcards
What are the different layers of your skin?
- Epithelium (epidermis): stratified squamous keratinized, stem cells
- Basement membrane
- Connective tissue (dermis)
- Fat (hypodermis)
What are the layers of the epidermis?
Stratum corneum (cornified or keratinized layer)
Dead cells, full of crosslinked keratin fibrils, amorphous substance
Stratum lucidum (clear layer)
Thin and variable, full of keratin , dead cells, no organelles
Stratum granulosum (granular layer)
Large keratohyalin granules, 3-5 layers of cells, associated with tonofibrils
Stratum spinosum (spiny layer)
Keratins in spiny processes, insert into desmosomes with tonofilaments
Stratum basale or germinativum (basal layer)
Cuboidal cells, replace skin epithelium every month (STEM CELLS), hemidesmosomes (integrins) for cell-matrix adhesion, desmosomes (cadherins) for cell-cell adhesion are made with collagen type VII, III and elastic fiber
What are 3 important cells in the epidermis of the skin?
- Melanocytes: melanin activated by UV, protects DNA, albinism = gene mutations in tyrosinase gene (complete or partial) Þ skin cancer
- Langerhans cells: dendritic cells, APC
- Merkel cells: mechanosensing cells, unmyelinated sensory nerve endings contact Merkel cells
Constituents of the dermis of the skin?
- Mesenchymal cell
- Fibroblast/Fibrocyte: building block of connective tissues (collagen is 3 α-chains in triple helix)
- Adipocyte
- Macrophage/Histiocyte
- Mast cell: secretory granules to send histamine, heparin, leukocyte chemoatractive factors
- Plasma cell
- Extracellular (Intercellular) Matrix
What is the wound healing sequence?
- Hemostasis
- Inflammation
- Cell proliferation/matric production (maturation)
- Remodeling
What happens during hemostasis?
- Vascular constriction, clot formation via platelet aggregation/degranulation and fibrin formation.
- The clot and surrounding wound tissue release pro-inflammatory cytokines and growth factors such as transforming growth factor beta (TGF-B), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF) and epidermal growth factor (EGF). Dried clot (fibrin eschar) can form at the surface of the wound, or if kept humid and bandaged, remains as a damp clot.
What happens during the inflammation phase of wound healing?
Neutrophil infiltration, monocyte infiltration and differentiation to macrophages, lymphocyte infiltration.
What happens during cell proliferation/matric production (maturation) of the wound healing sequence?
- Re-epithelialization by keratinocytes, angiogenesis, fibroblast proliferation and extracellular matrix production, (collagen) in the dermis.
- Players: TGF-β1 (important ligand and growth factor), EGF, KGF, TGF-α, VEGF
What happens during the Remodeling phase of wound healing sequence?
Extracellular matrix remodeling, vascular maturation, contraction and regression
What factors influence wound healing?
- oxygenation
- hair density (++ stem cells in hair follicles)
- scab formation (not favourable)
- sexe hormones
- stress
- diabetes
- medication
What goes wrong in the healing procress of hypertrophic and keloids scars?
- Overabundance of collagen in the dermis
- Prolonged inflammatory response that leads to increased and sustained ECM production
- Fibroblasts have increased growth factor receptors and respond more readily to TGF-β
Characteristics of Scleroderma?
- Autoimmune disease, localized (skin) and systemic (skin and internal organs)
- Thickening, swelling and tightening of the skin from increased collagen (fibrosis)
- Increased TGF-β and receptors
Papillary layer
Sweat duct
Loose connective tissue
Henle’s layer
Stratum Granulosum
Secretary portion of sweat gland
E
Stratum spinosum
Dense irregular connective tissue
It’s just a fucking nail bed
