Chapter 5 - The Integumentary System

Structure of Hair Follicle

- Follicle: Fold down from epidermal surface into the dermis - wall is composed of out peripheral connective tissue sheath and inner epithelial root sheath - Hair Bulb: forms from deep end of follicle, cell division takes place - Hair follicle receptor (root hair plexus): Knot of sensory nerve endings that wrap around hair bulb - Hair papilla: Nipple-like bit of dermal tissue that protrudes into hair bulb, supplies nutrients - Hair Matrix: Actively dividing area of hair bulb that produces hair originate in hair bulge - Arrector Pili: Bundle of smooth muscle cells, goose bumps, makes hair stand up, part of thermoregulation in some mammals

Skin Functions

- Protection: chemical, biological & physical barriers - Body Temperature Regulation - Cutaneous Sensation - Metabolic Functions - Blood Reservoir - Excretion

Types and Growth of Hair

- Vellus Hair: Body hair of children and adult females, pale & fine - Terminal hair: Coarser, longer hair of eyebrows and scalp, puberty hair

Hairs

Also called pili - Flexible strands produced by hair follicles and consist largely of dead, keratinized cells. Chief regions: - Shaft: Keratinization is complete, projects from skin, extends halfway down portion of hair embedded in skin - Root: Keratinization is ongoing, remainder of hair deep in follicle

Epidermis

Avascular - Composed of epithelial cells, outermost protective shield of the body. Epidermal derivatives.

Flexure lines

Dermal folds that occur at or near joints where the dermis is tightly secured to deeper structures (deep creases on palms)

Growth Cycle of Hair

Grow, stop, fall out, reorganize new

Carotene

Yellow to orange pigment found in certain plant products (carrots) - Accumulates in stratum corneum. Can be converted to Vitamin A (essential for vision)

Sweat Glands

Sudoriferous Glands - Distributed over entire skin surface except nipples and external genitalia. 2 Types: - Eccrine (Merocrine): Far more numerous, abundant on palms, soles of feet and forehead. Secretory part lies coiled in dermis and duct extends into funnel-shaped pore - Apocrine: Confined to axillary anogenital areas, ducts empty into hair follicles (sweat plus fatty substances and proteins) - Body odor! Ceruminous glands line external ear canal (ear wax) Mammary glands (milk)

Stratum Lucidum

Clear layer, visible only in thick skin - Just above stratum granulosum, 203 layers of clear, flat, dead keratinocytes with indisctict boundaries. Dead, thick skin or callas, translucent

Layers of Hair's Keratinized Cells

Cross section: - Medulla: Central Core, large cells and air spaces - Cortex: Bulky layer surround medulla, several laters of flattened cells - Cuticle: Outermost layer, single later of cells overlapping one another

Reticular Layer

Deeper layer of dermis - Coarse, dense irregular connective tissue. Cutaneous Plexus (network of blood vessels that nourishes this layer) separates from hypodermic. Between collagen bundles are cleavage (tension) lines that are externally invisible lines that run longitudinally in the skin of the head and limbs and in circular patters around neck and trunk.

Skin Appendages

Derivatives of the epidermis: hair and hair follicles, sweat glands, and sebaceous (oil) glands

Keratin

Fibrous protein that helps give the epidermis its protective properties - made up of keratinocytes which are connected by desmosomes (most epidermal cells)

Nail

Hard Keratin, has: - Free edge - Nail Plate - Body: Visibly attached portion - Root: Embedded in skin - Nail Bed: deep laters of epidermis that extend beneath nail - Nail Matrix: Thickened proximal portion of nail bed, responsible for nail growth - Nail Folds: Lunule: White crescent - Cuticle (eponychium): Proximal nail fold projected onto nail body - Hyponychium: Thickened region beneath free edge of nail where dirt sticks

Stratum Corneum

Horny layer. Most superficial layer; 20-30 layers of dead cells, essentially flat membranous sacs filled with keratin. Glycolipids in extracellular space. Protect the skin against abrasion and penetration. Shingle-like cornified or horny cells (dandruff). Thin, flat, dead, usually no nucleus. Thicker in thick.

Stratum Granulosum

Typically one to five layers of flattened cells, organelles deteriorating; cytoplasm full of lamellar granules (lipid protein, release lipids) and keratohyline granules (beginning production of keratin). Keratinization occurs (cells flatten, nuclei and organelles begin to disintegrate, and they accumulate both granules above.

Dermis

Vascularized, underneath epidermis, making up the bulk of the skin. Tough, leathery layer composed of mostly dense connective tissue.

Basal Cell Carcinoma

Most common - Stratum basal cells proliferate, invading dermis and hypodermic. Lesions appear on face as shiny dome-shaped nodules that later develop central ulcer with a pearly, beaded edge

Melanoma

Most dangerous - Cancer of melanocytes, resists chemotherapy (Asymmetry, Border Irregularity, Color, Diameter)

Subcutaneous

Not a part of the skin, however shares some of the skin's protective function. Also called superficial fascia and Hypodermis because it is superficial to the tough connective tissue wrapping of the skeletal muscles, consists mostly of adipose tissue. Vascular

Stratum Basale

One layer. Also called Stratum Germinative. Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and dendritic cells. Continuously renews cell population.

Melanin

Polymer made of tyrosine amino acids - Synthesis depends on an enzyme in melanocytes called tyrosinase and it passes from melanocytes to the basal keratinocytes. Prolonged sun exposure causes substantial melanin buildup by absorbing the rays, leading to protecting the DNA

Squamous Cell Carcinoma

Second most common - Arises from keratinocytes of stratum spinosum. Lesions appear as scaly reddened papule that arise most often on the head and hands

Stratum Spinosum

Several layers of keratinocytes unified by desmosomes. Cells contain thick bundles of intermediate filaments made of pre-keratin. Several cell layers thick. Spiny, keritinyzed, tough & water proofing

Tactile Cells

Shaped like a spike hemisphere - Also called Merkel cells, present in epidermal-dermal junction. Sensory receptor for touch.

Sebaceous (Oil) Gland

Simple branched alveolar glands found all over body except in thick skin of palms and soles - secrete sebum. Central cells of alveoli accumulate oily lipids until they become so engorged that they burst. Keeps things lubricated

Melanocytes

Spider-shaped epithelial cells that synthesize the pigment, melanin, found in the deepest layer of the epidermis. Accumulate on the superficial side of keratinocyte nucleus forming pigment shield that protects nucleus from damaging effect of UV radiation

Dendritic Cells

Star-shaped, arise from bone marrow and migrate to epidermis. Also called Langerhans cells, ingest foreign substances and are key activators for our immune system

Layers of Epidermis

Thick skin = Covers areas subject to abrasion - Palms, fingertips, soles of feet. 5 layers, deep to superficial: - Stratum Basale - Stratum Spinosum - Stratum Granulosum - Stratum Lucidum - Stratum Corneum

Papillary Layer

Thick superficial layer of dermis, areolar connective tissue in which fine interlacing collagen and elastic fibers form a loosely woven mat that is heavily invested with small blood vessels. Dermal Paillae, projections, are on surface contain touch receptors (tactile or Meissner's corpuscles) which lie atop friction ridges (fingerprints)

Burn

Tissue damage inflicted by intense heat, electricity, radiation, or certain chemicals, all of which denature cell proteins and kill cells in the affected areas. Threat to life: Loss of proteins and electrolytes. 1st Degree: Only epidermis 2nd Degree: Epidermis and upper region of dermis, blisters 3rd Degree: Full-thickness burns, blackened