Integumentary System Quiz

Skin (Integument)

• Consists of two distinct regions: epidermis (superficial epithelial tissue) and dermis (underlies epidermis, mostly fibrous connective tissue)
• Hypodermis (subcutaneous layer) is deep to the skin, not part of skin but shares functions. It's mostly adipose tissue, absorbing shock and insulating, anchoring skin to structures (mostly muscles)

Epidermis

• Keratinized stratified squamous epithelium
• Four or five distinct layers: stratum basale, stratum spinosum, stratum granulosum, stratum lucidum (only in thick skin), and stratum corneum
• Four cell types: keratinocytes, melanocytes, dendritic (Langerhans) cells, and tactile (Merkel) cells

Keratinocytes

• Produce fibrous protein keratin (most epidermis cells)
• Tightly connected by desmosomes
• 10-25% of cells in deepest epidermis
• Produce pigment melanin - packaged into melanosomes
• Protect apical surface of keratinocyte nucleus from UV damage

Dendritic (Langerhans) cells

• Macrophages (key activators of immune system)

Tactile (Merkel) cells

• Sensory touch receptors

Stratum Basale (Basal Layer)

• Deepest epidermal layer, also called stratum germinativum
• Firmly attached to dermis
• Single row of stem cells actively mitotic, producing two daughter cells
• Takes 25-45 days for one cell to move from basal layer to the surface where it dies
• One cell remains in stratum basale as a stem cell
• Melanocytes compose 10-25% of this layer

Stratum Spinosum (Prickly Layer)

• Several layers thick
• Cells contain web-like system of intermediate prekeratin filaments attached to desmosomes
• Abundant melanosomes and dendritic cells

Stratum Granulosum (Granular Layer)

• Thin (four to six cell layers)
• Cell appearance changes: cells flatten, nuclei and organelles disintegrate, keratinization begins
• Cells accumulate keratohyaline granules (help form keratin in upper layers)
• Cells accumulate lamellar granules (their water-resistant glycolipid slows water loss)
• Cells above this layer die (too far from dermal capillaries)

Stratum Lucidum (Clear Layer)

• Only in thick skin
• Thin, translucent band superficial to the stratum granulosum
• A few rows of flat, dead keratinocytes

Stratum Corneum (Horny Layer)

• 20-30 rows of dead, flat, anucleate keratinized membranous sacs
• Three-quarters of epidermal thickness
• Though dead, its cells protect deeper cells, prevent environment and water loss, abrasion, and penetration
• Provides barrier against biological, chemical, and physical assaults

Dermis

• Strong, flexible connective tissue
• Cells: fibroblasts, macrophages, mast cells, and white blood cells
• Fibers in matrix bind body together (“Hide” used to make leather)
• Contains nerve fibers, blood/lymphatic vessels
• Contains epidermal hair follicles, oil and sweat glands
• Two layers: papillary and reticular

Papillary Layer of Dermis

• Areolar connective tissue
• Collagen and elastic fibers and blood vessels
• Loose tissue — phagocytes patrol for microorganisms
• Dermal papillae – superficial peglike projections

Dermal Papillae

• Most contain capillary loops
• Some contain Meissner's corpuscles (touch receptors)
• Some contain free nerve endings (pain receptors)
• In thick skin, lie atop dermal ridges that cause epidermal ridges (friction ridges)
• Enhance gripping ability
• Contribute to the sense of touch
• Pattern is fingerprints

Reticular Layer of Dermis

• ~80% of dermal thickness
• Dense fibrous connective tissue
• Elastic fibers provide stretch-recoil properties (strength and resiliency)
• Bind water (cleavage lines because most collagen fibers run parallel to skin surface)
• Externally invisible, important to surgeons
• Incisions parallel to cleavage lines gap less and heal more readily

Flexure lines

• Dermal folds at or near joints
• Dermis is tightly secured to deeper structures
• Skin cannot slide easily for joint movement causing deep creases
• Visible on hands, wrists, fingers, soles, toes

Other Skin Markings

• Striae: silvery-white scars ("stretch marks") from extreme stretching causing dermal tears
• Blisters: from acute, short-term trauma, fluid-filled pocket that separates epidermal and dermal layers

Skin Color

• Three pigments: melanin, carotene, hemoglobin
• Melanin: only pigment made in skin (two forms- reddish-yellow to brownish-black)
• Color differences due to amount and form
• Produced in melanocytes (same relative number in all people)
• Migrates to keratinocytes to form "pigment shields"
• Freckles and pigmented moles (local accumulations of melanin)
• Sun exposure stimulates melanin production
• Sunspots (tinea versicolor) are fungal infection (not related to melanin)
• Carotene: yellow to orange pigment (most obvious in palms and soles), accumulates in stratum corneum and hypodermis, can be converted to vitamin A for vision and epidermal health
• Hemoglobin: pinkish hue of fair skin

Appendages of the Skin

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

Hair

• Dead keratinized cells of hard keratin (more durable)
• Not in palms, soles, lips, nipples, portions of external genitalia
• Functions: warn of insects, physical trauma, heat loss, sunlight
• Hair pigments: melanins (yellow, rust, brown, black); trichosiderin (red hair)
• Gray/white hair: decreased melanin production, increased air bubbles in shaft

Hair Follicles

• Extend from epidermis to dermis
• Two-layered wall (part dermis, part epidermis)
• Hair bulb (expanded deep end, hair follicle receptor (root hair plexus), sensory nerve endings - touch receptors hair matrix (actively dividing area)
• Arrector pili (smooth muscle attached to follicle, responsible for "goose bumps")
• Hair papilla (dermal tissue – blood supply)

Nails

• Scalelike modifications of epidermis
• Protective cover for distal, dorsal surface of fingers and toes
• Contain hard keratin
• Nail matrix (hair growth)

Sweat Glands

• Also called sudoriferous glands
• All skin surfaces except nipples and parts of external genitalia
• ~3 million per person
• Two main types: eccrine (merocrine) and apocrine sweat glands
• Eccrine sweat glands are most numerous, abundant on palms, soles, and forehead; ducts connect to pores; function in thermoregulation (regulated by sympathetic nervous system), secretion is mostly water
• Apocrine sweat glands are larger than eccrine glands, confined to axillary and anogenital areas, their secretion contains fatty substances, proteins and are odorless until bacterial interaction = body odor, ducts empty into hair follicles, become functional at puberty

Sebaceous (Oil) Glands

• Widely distributed (not in thick skin of palms and soles)
• Most develop from hair follicles and secrete into hair follicles
• Relatively inactive until puberty (stimulated by hormones, especially androgens)
• Secrete sebum (oily holocrine secretion, bactericidal and softens hair and skin)

Functions of the Integumentary System

• Protection (chemical, physical, biological barriers)
• Body temperature regulation
• Cutaneous sensation (sensory receptors)
• Metabolic functions (vitamin D synthesis, chemical conversion carcinogens)
• Blood reservoir (up to 5% of body's blood volume)
• Excretion (nitrogenous wastes and salts in sweat)

Skin Cancer

• Most skin tumors are benign and do not metastasize
• Risk factors: overexposure to UV radiation, frequent irritation of skin
• Some lotions contain enzymes that repair damaged DNA
• Three major types: basal cell carcinoma, squamous cell carcinoma, and melanoma
• Basal cell carcinoma: least malignant, most common, stratum basale cells proliferate, slowly invade dermis and hypodermis, cured by surgical excision in 99% of cases
• Squamous cell carcinoma: second most common type, involves keratinocytes, usually scaly reddened papule, does metastasize, good prognosis if treated by radiation therapy/removed surgically
• Melanoma: cancer of melanocytes, highly metastatic and resistant to chemotherapy, treated by wide surgical excision accompanied by immunotherapy, crucial is early detection using ABCD rule (Asymmetry, Border irregularity, Color, Diameter)

Burns

• Tissue damage from heat, electricity, radiation, certain chemicals
• Denatures proteins, kills cells
• Immediate threat: dehydration, electrolyte imbalance, leads to renal shutdown and circulatory shock
• To evaluate burns: Rule of Nines (estimates volume of fluid loss)
• Burns are classified by severity: first degree (epidermal damage only, localized redness + edema), second degree (epidermal and upper dermal damage, blisters appear), third degree (entire thickness of skin involved, skin gray-white, cherry red, or blackened, not painful)

Severity and Treatment of Burns

• Critical if >25% body has second-degree, >10% third-degree burns (Face, hands, or feet bear third-degree burns)
• Treatment includes debridement, antibiotics, temporary covering, and skin grafts

Selected Imbalances, Disorders, and Diseases Affecting the Skin

• Epidermolysis bullosa: inherited disorders in which skin blisters develop in response to minor injury
• Psoriasis: common skin condition causing skin redness and irritation
• Contact dermatitis: inflammation of skin caused by direct contact irritating substance
• Pressure ulcers: area of skin breaks down from staying in one position for too long without shifting weight
• Folliculitis: inflammation of one or more hair follicles
• Acne: skin condition characterized by whiteheads, blackheads, and inflamed red pimples
• Albanism: no skin pigment
• Jaundice: common in newborns, yellow color skin/whites of eyes caused by excess bilirubin in the blood
• Other related conditions and diseases...

Developmental Aspects

• Fetal: ectoderm → epidermis; mesoderm → dermis + hypodermis; lanugo coat; vernix caseosa
• Infancy to adulthood: skin thickens, sweat/sebaceous glands activity increases, effects of environmental assaults, scaling, and dermatitis more common
• Aging: epidermal replacement slows, skin becomes thin/dry, subcutaneous fat/elasticity decrease (cold intolerance + wrinkles), increased risk of cancer (decreased numbers melanocytes/ dendritic cells), hair thinning)