Epidermis and Dermis
Epidermis
Mostly dead (due to lack of vascularization or blood vessels), keratinized cells (stratified squamous), which lends itself to a protective, waterproof barrier
Layers (from deep to superficial)
- Stratum Basale
- 1 layer thick of cuboidal and columnar cells with pigment
- Also known as “Stratum Germinativum” due to the presence of basal skin stem cells, which differentiate into keratinocytes (KCs) that “germinate” and replenish dead skin cells
- Attached to underlying basement membrane via hemidesmosomes
- Stratum Spinosum
- 8-10 layers of KCs
- “Spiny layer” due to histological pincushion-like appearance of cells due to the shrinking of cytoplasm and the termination of tonofibrils
- Presence of langerhan cells (dendritic APCs)
- Stratum Granulosum
- 3-5 layers of flattened KCs
- Presence of keratohyalin and lamellar granules (golgi-derived glycolipids that confer water-resistance of skin)
- Stratum Lucidum (only present in thick, glabrous skin)
- KCs are flat, dense, no organelles
- Stratum Corneum
- 15-30 layers of KCs
- Shed in layers due to desmosome connections
- Squames: fully keratinized and cornified cells that are shed continuously
Helpful mnemonic! British and Spanish Grannies Love Cornflakes
Dermis
Is vascularized tissue (with blood supply), so cells are alive
High amounts of collagen and elastic fiber lead to flexibility and resilience of skin
Papillary Layer
- Type I, III collagen
- Mast, dendritic, and langerhans cells
- Connected to epidermis via anchoring fibrils of Type VII collagen
Reticular Layer
- Meshwork of irregular connective tissue with Type I collagen
- High concentration of proteoglycans with dermatan sulfate
Indistinct layer between papillary and reticular layer due to blending of collagen fibers
Dermal plexuses (blood supply)
- Cutaneous plexus: along border of hypodermis and reticular layer; supplies adipose tissue, integument, accessory structures of dermis
- Subpapillary plexus: along border of epidermis and papillary layer
Amytomically 
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