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1. BIO 210 Handout #6 - Skin (Integument) Function: prevents water loss from body surface regulates heat loss from body surface mini-excretory system – urea, salt, water site of vitamin D synthesis Cutaneous sense organs – pain, pressure, light touch, heat Insulates & cushions underlying body tissues Protects against: mechanical damage – bumps, cuts chemical damage – acids, alkalis thermal damage bacterial invasion 3 clearly defined layers of the skin: 1) Epidermis – most superficial layer Tissue: Keratinized stratified squamous epithelium consisting of 4 cell types – 1) keratinocytes – major cell; produces keratins making skin durable and protective 2) melanocytes produce melanin, protective pigment that shields DNA from UV radiation 3) Langerhans’ cells – phagocytize bacteria, part of immune system 4) Merkel cells –sensitive touch receptors Epidermis has 4 or 5 layers of cells – 1) Stratum basale – deepest layer; a single row of cuboidal cells constantly undergoing mitosis; contains melanocytes 2) Stratum spinosum - cell layers superficial to basal layer, cells appear spiky; cell division still occurs - nutrients still diffuse from dermis 3) Stratum Granulosum – thin layer full of granules cells begin to die 4) Stratum lucidum – very clear; thin translucent band found only on palms & soles (thick skin) 5) Stratum corneum – cornified or horny layer; no nucleus or organelles flattened scale like cells full of keratin; constantly rubbed off and replaced by deeper cells #5 #4 #3 #2 #1 • Dermis – middle layer • ` Tissue: dense irregular connective tissue heavy collagen & elastic fibers • Two principal regions • 1) Papillary layer – most superficial; thin layer of areolar connective tissue • fingerlike projections (dermal papilla) attach to the epidermis • unique patterns of ridges = fingerprints; • capillary networks furnish nutrients to epidermis; • pain & touch receptors found here • 2) Reticular layer – dense irregular connective tissue • contains many arteries, veins, sweat & sebaceous • glands, and pressure receptors 3) Hypodermis – deepest layer; primarily adipose tissue 1 of 3

2. Appendages of the skin – hair, nails & Cutaneous glands all originate from the Stratum basale and grow downward into the deeper skin regions Meissner’s corpuscle Epidermis (stratified squamous) Papillary Dermis (areolar CT) Reticular Dermis (Dense irregular CT) Hypodermis (adipose tissue) Pacinian corpuscle Eccrine sweat glands • Pacinian corpuscle – deep pressure receptor • located in the reticular layer of the dermis; looks like an onion cut lengthwise; • Meissner’s corpuscle –light touch receptor • located in the dermal papilla of the papillary layer; looks like small tornado • Hair root – portion of the hair enclosed within the follicle • Hair shaft - portion projecting above the scalp surface • Hair follicle – connective tissue sheath provides nutrition for the • growing hair; starts in reticular layer • Sebaceous gland – ducts empty into hair follicle; • Sebum is oily lubricant that keeps skin soft and moist • Arrector pili muscle – small bands of smooth muscle • Connect hair follicle to the papillary layer of the dermis; • Contraction = goose bumps are formed • Suderiferous gland – sweat glands; Two kinds: • Eccrine – clear perspiration containing water, salts & urea • located all over the body • Apocrine – perspiration containing milky proteins and fat-rich substances; found in the axillary & genital areas 2 of 3

3. AP – arrector pili D – dermis d - duct E – epidermis H – hair shaft hD - hypodermis HF – hair follicle Sg – sebaceous gland Swg – eccrine sweat gland 3 of 3