INTEGUMENTARY SYSTEM

Epidermal Ridges

= "Curves" of stratum basale that allows increased contact with dermis = Complements "curves" of dermal papillae of dermis = Pattern of ridges are genetically determined = Ridges on thick skin are identifying (e.g., fingerprint)

Hair Growth Stage

= 2-6 years = Matrix at root produces length = Pushes dead hair out as new cycles begin

Hair Resting Stage

= 3 months = Matrix cells inactive (club hair); follicle atrophies

Epidermis

= 4 cell types (keratinocytes, melanocytes, merkel cells, langerhans cells) = 4-5 layers 1. Stratum cornea (superficial) 2. Stratum lucidum (thick skin only) 3. Stratum granulosum 4. Stratum spinosum 5. Stratum basale (deepest)

Hair Root

= Attaches hair follicle to hair shaft = Extends into dermis = Site of cell division

Melanin

= Black, brown or yellow-brown pigment produced by melanocytes = Forms in intracellular vesicles (melanosomes) = Absorbs UV radiation = Neutralizes free radicals

Root Hair Plexus

= Bundle of sensory nerves around base of hair follicles = Like sensory whiskers (vibrissae) in animals

Stratum Lucidum

= Clear layer of epidermis (thick skin only) = Cells lack nucleus and organelles = Cells are flattened, dense, filled with keratin filaments parallel to surface

Apocrine Sweat Gland

= Coiled tubular glands; duct opens to hair follicle = Viscous, cloudy, odorous secretion = Produced by MEROCRINE mode of secretion! = Contains myoepithelial cells that squeeze gland to discharge secretion = Does not function until puberty LOCATION: Armpits, nipples, groin; male facial hair

Hair Follicle

= Consists of internal root sheath, external root sheath and glassy membrane (around hair)

Keratohyalin Granules

= Contains lamellar granules that secrete lipids that coat cells in stratum granulosum = Lipids prevent nutrients from diffusing to superficial layers of skin FUNCTION: Create water resistance, protection

Keratohyalin

= Converts tonofilaments into keratin = Forms keratohyalin granules = Increased friction increases production → callus

Nail Body

= Covers nail bed

Reticular Layer

= Deep layer of dermis = Dense irregular CT with interwoven meshwork of collagen and elastic fibers = Packed with oil and sweat (sudoriferous) glands, fat and hair follicles = Collagen fibers extend into papillary layer to connect layers FUNCTION: Provide strength and elasticity

Stratum Basale

= Deepest layer of epidermis (single layer) = Attached to basal lamina = Mostly large stem cells (basal cells) CONTAINS: Basal cells, melanocytes, and merkel cells

Stratum Spinosum

= Epidermal layer 8-10 cells thick = Superficial to stratum basale = Stem cells from basale differentiate into keratinocytes = Adjacent keratinocytes connect via desmosomes and tonofibrils CONTAINS: Keratinocytes, melanocytes, langerhans cells

Hair Bulb

= Epithelial cells surrounding hair papilla = Germinal cell layer

External Sheath

= Epithelial layer extending from skin surface to hair matrix

Hair Matrix

= Epithelium that produces hair components = Superficial basal cells divide and push up to develop hair

Hair Shaft

= Extends from hair root (halfway to skin surface) to outside

Lanugo Hair

= Extremely fine and unpigmented = Shed before birth

Vellus Hair

= Fine "peach fuzz" hairs = No distinct medulla LOCATION: All over body

Hyponychium

= Free edge of nail

Accessory Structures

= Hair follicles, nails, sebaceous glands, sweat glands

Intermediate Hair

= Hairs that change in their distribution = No distinct medulla LOCATION: Upper and lower limbs

Terminal Hair

= Heavy, more deeply pigmented, and sometimes curly LOCATION: Head, eyebrows, lashes

Medulla

= Innermost core of hair shaft (terminal hairs only) = Made of soft, flexible keratin = 2-3 rows of polyhedral cells = Contains pigment granules and air spaces

Sebaceous Follicles

= Large sebaceous glands that secretes sebum directly onto surface of skin = Does not produce hair = Bacterial infection can cause inflammation (folliculitis) or boils (furuncles) LOCATION: E.g., back, face, chest, nipples

Dermis

= Layer deep to epidermis = Composed of two layers (papillary and reticular) = Nourishes epidermis via diffusion

Stratum Granulosum

= Layer superficial to stratum spinosum (3-5 thick) = Most superficial layer with nucleated cells (degenerating nuclei → apotosis = programmed cell death) = Cells begin to manufacture keratohyalin and lamellar granules CONTAINS: Keratinocytes

Cortex

= Middle ring of hair shaft = Hard keratin; elongated cells with pigment granules (dark hair) and/or air (white/gray hair) = Major portion of hair shaft

Keratinocyte

= Most abundant cells in epidermis = Contains tonofibrils for attachment to adjacent keratinocytes LOCATION: Component of most layers (except lucidum and basale strata)

Stratum Corneum

= Most superficial layer of epidermis (25-30 thick) = Dehydrated (dead) cells lack nucleus and organelles = Water-resistant, but insensible perspiration occurs CONTAINS: Layers of dead keratinocytes

Eponychium

= Nail cuticle

Sebum

= Oily secretion from sebaceous gland = Provides lubrication = Antimicrobial

Carotene

= Orange-yellow pigment; can be converted to vitamin A = Accumulates in keratinocytes; especially evident in stratum corneum

Hair Cuticle

= Outermost ring of hair shaft = Dead keratin cell coat

Lunula

= Pale crescent at bottom of nail body

Hair Papilla

= Peg of connective tissue containing capillaries and nerves

Melanocyte

= Pigment-producing cells in epidermis = Converts tyrosine to melanin via tyrosinase = Color determined by melanocyte activity, not amount LOCATION: Basale and spinosum strata

Nail Matrix

= Produces growth = Cells transformed into tightly packed keratinized cells = 1mm per week LOCATION: Below nail root

Tonofibrils

= Protein filaments that extended across keratinocytes to desmosomes, connecting adjacent cells in stratum spinosum = Act as cross-braces, supporting cell junctions

Ceruminous Gland

= Secretes waxy cerumen into external ear canal

Merkel Cells

= Sensation-detecting cells in epidermis via touch receptors (tactile discs) LOCATION: Stratum basale and skin surfaces that lack hair FUNCTION: Release chemicals that stimulate sensory nerve endings

Arrector Pili

= Smooth muscle in dermis connectins papillary dermis to hair follicle = Contracts with cold or fear → goosebumps

Papillary Layer

= Superficial layer of dermis (top 20%) = Loose CT, hair follicles, glands, nerves; highly vascularized = Has touch receptors (Meissner's Corpuscles = combination of merkel cells and neurons) = Has ridges that complement epidermal ridges FUNCTION: Anchors epidermis to dermis

Internal Sheath

= Surrounds hair = Disintegrates quickly = Doesn't span entire hair (root to sebaceous gland)

Glassy Membrane

= Thickened basal lamina wrapped in dense CT sheath

Langerhans Cells

= aka Dendritic Cells = Phagocytic wandering cells in epidermis LOCATION: Stratum Spinosum

Merocrine Sweat Gland

= aka Eccrine Sweat Gland = Coiled, tubular gland; duct opens to skin surface = Numerous, widely distributed = Clear secretion: mostly H₂O, NaCl, NH₃ and urea

Subcutaneous Layer

= aka Hypodermis or Superficial Fascia = Loose CT with abundant adipocytes = Interwoven with reticular layer = Elastic; highly vascularized = Site of subQ injections → bloodstream

Sebaceous Gland

= aka Oil Gland = Discharges a waxy, oily secretion (sebum) into hair follicles = Manufactures abundance of lipids; holocrine secretion = Short ducts; several to one follicle possible