NS 3410 1st Edition Lecture 7Outline of Last LectureI. Overview of Integumentary SystemII. Epithelial TissueIII. Skin Regions IV. Skin ColorOverview of Current LectureI. Cells in SkinII. Layers of Epidermis III. DermisIV. HypodermisV. AgingVI. Skin CancerCurrent LectureI. Cells in Skin- In the stratum basale layer of the epidermis there are Merkel cells, which are tactile discs (sense touch)- In the papillary layer of dermis are Meissner’s corpuscle which are mechanoreceptors that are sensitive to light touch-Also in the dermis are the Pacinian corpuscle (mechanoreceptor that responds to acute deep pressure) and Raffini corpuscle (responds to deep pressure)II. Layers of EpidermisThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Stratum Basale (Basal Layer)-Deepest epidermal layer firmly attached to dermis-Typically a single layer of cells; contains the youngest keratinocytes-Cells undergo rapid division-10 to 25% of cells in this layer are melanocytes-This layer forms epidermal ridges; ridge patterns basis for fingerprints- Stratum Spinosum (Prickly Layer)-Several layers thick-Cells contain a web-like system of intermediate filaments attached to desmosomes -Keratinocytes are irregular in shape-Melanin granules and Langerhans cells are abundant in this layer - Stratum Granulosum-Thin; three to five cell layers-Cells become flattened; intracellular organelles disintegrate-Too far from dermis so can’t get nutrients-Cells have stopped dividing-Accumulate keratohyaline and lamellated granules - Stratum Lucidum (Clear Layer)-Thin, transparent band superficial to stratum granulosum-Consists of a few rows of flat, dead keratinocytes-Present only in thick skin-Gummy keratohylaine granules cause cells to stick in parallel- Stratum Corneum (Horny Layer)-Outermost layer of keratinized cells-Accounts for three quarters of the epidermal thickness-Functions: waterproofing, protection from abrasion and penetration, rendering the body relatively insensitive to biological, chemical and physical assaults- It takes 15-30 days for cells to move from stratum basale to stratum corneum- Dead cells stay in stratum corneum for up to 2 weeks before being shed or washed away- Surface relatively dry-not conductive to microorganism growth- Barrier maintenance helped by secretion of lipid from sebaceous glands- Lose about 500 mL of water from surface every dayIII. Dermis- Second major skin region containing strong, flexible connective tissue- Cell types include fibroblasts, macrophages, sometimes mast cells and white blood cells- Composed of two layers: papillary and reticular- Papillary Layer-Thin, superficial layer; 20% of dermis-Areolar connective tissue with collagen and elastic fibers-Its superior surface contains peg-like projections called dermal papillae-Dermal papillae contain capillary loops, Meissner’s corpuscles and free nerve endings- Reticular Layer-Accounts for 80% of thickness of dermis-Dense, irregular connective tissue-Collagen fibers in this layer add strength and resiliency to the skin-Elastin fibers provide stretch-recoil properties-Tension fibers- separations from underlying collagen fiber bundles - Contains hair follicles, arrector pili muscles; contraction causes hair to stand erect= goose bumpsIV. Hypodermis- Subcutaneous layer deep to the skin- Not really part of the skin= superficial fascia- Composed of adipose and areolar connective tissue, anchoring skin to underlying structuresV. Aging- Aging results in the following consequences on skin:-Thinning: stratum basale activity declines-Sensitivity to infection: dendritic cells decrease, skin repair slower-Hormone production: less D produced-Pale skin: melanocyte activity declines-Dry skin: glandular activity declines-Always cold: blood supply and sweat gland function decreased-Hair follicles: stop functioning or make thinner, finer hair-Wrinkling: elastic fibers decrease in size and networkVI. Skin Cancer- UV radiation that reaches the earth’s surface is made up of UVA and UVB rays-UVB rays are more likely than UVA rays to cause sunburn, but UVA rays pass deeper intothe skin-Both can lead to skin cancer- Melanoma reflects following in moles: asymmetry, border irregularity, color, diameter greater than ¼ inch, evolving-Melanoma is a malignant tumor which originates in melanocyte cells, which produce melanin-The majority of melanomas are black or brown- Malignant Melanoma is the most dangerous type of skin cancer because it is highly metastatic, resistant to chemotherapy- Basal Cell Carcinoma:-Least malignant and most common-Accounts for over 75% of all skin cancers-Stratum basale cells proliferate and invade the dermis and hypodermis-Slow growing and do not often metastasize-Can be cured by surgical excision in 99% of the cases- Squamous Cell Carcinoma also