> making up 16% of our total body weight, the skin provides protection (e.g. UV, mechanical, chemical, thermal, pathogens), thermoregulation, and Vitamin D synthesis ![[Pasted image 20250111143902.png | Figure 1: Layers of the skin with adnexal structures]] ## Embryology - Epidermis: derived from ectoderm - Dermis: derived from mesoderm - Immigrant cells: - Melanocytes: originate from the neural crest - Langerhands cells: originate from the mesenchymal (precursor in bone marrow) ## Histology ![[Pasted image 20250111145847.png | Table 1: Contents of skin layers]] - Full-thickness skin: 1,500-4,000 um ### Epidermis - Thickness: dependent on location, averaging 100 um - Major cell: Keratinocyte - Differentiate in 28-45 days, progressing from basal proliferative germinal layer to dead cornified layer ![[Pasted image 20250111150357.png | Table 2: 5 layers of the epidermis]] ### Dermis - Thickness: highly variable depending on location, thicker on the scalp and thinnest on eyelids - 2 layers: - Papillary dermis - Thickness: ~100 um - begins at basement membrane, base of epidermis - [[Collagen]] content: high in type III - No mature elastic fibers - Collagenase activity - Reticular dermis - Thickness: 2000-2500 um - extends from papillary dermis to the hypodermis - Collagen content: type I in large fibers and bundles - [[Elastin]] bands connect bundles together - both elastic and collagen bundles thicken toward the hypodermis - Also contain ground substance - gel-like material, made up of hyaluronic acid and proteoglycans, that permits diffusion of metabolites ## Vascularity and Cutaneous Nerves ![[Pasted image 20250111161052.png | Figure 2: Vascular plexuses and cutaneous nerves]] Receptor types: • Mechanoreceptors - Touch - Pressure - Vibration - Stretch • Thermoreceptors • Chemoreceptors • Nociceptors (mostly raw/free nerve endings) > [[Aging Skin]] demonstrates poorer injury healing and other functional capacities correlating with worsening appearance > [[Genetics Disorders of the Skin]] show varied response to surgical rejuvenation #basicscience #anatomy #Plastics