ch6 - integumentary system ai

Largest and heaviest organ

Skin; 1.5–2 m², 10–11 lbs, 16% of body weight

Average thickness of skin

0.5 mm to 6 mm; varies with abrasion

Two major components of skin

Cutaneous membrane (covers body surface), Epidermis (superficial), Dermis (deep)

Accessory structures of skin

Sweat glands, sebaceous glands, hair, nerve endings

Subcutaneous tissue (hypodermis)

Loose connective tissue + adipose tissue; not part of skin

Function of skin

Resistance to trauma and infection; contains keratin, spot desmosomes, acid mantle, defensins, dermicidin

Barrier functions of skin

Prevents excess water absorption/loss, protects from UV light and chemicals

Vitamin D synthesis

Skin produces cholecalciferol (vitamin D3) as first step in production

Sensation

Detects heat, cold, touch, texture, pressure, vibration, and pain; greatest sensitivity in face, palms, fingers, soles, nipples, genitalia

Thermoregulation

Blood flow and sweat control heat loss; conserve heat in cold via blood flow reduction

Nonverbal communication

Skin changes with facial expressions

Excretion

Skin removes organic wastes (salt, water, urea, ammonia, uric acid, CO₂) via sweat

Absorption

Lipid-soluble substances (steroids, vitamins A/D/E/K, toxins) can be absorbed

Coordination of immune responses

Defense against pathogens and skin cancers

Epidermis tissue type

Stratified squamous epithelium; avascular; nutrients from dermis via diffusion

Epidermal nutrient diffusion

Deep cells near dermis get nutrients faster → higher metabolism; superficial cells slower → lower metabolism

Primary epidermal cell types

90% keratinocytes; also melanocytes, dendritic cells, tactile epithelial cells

Thin skin layers

Stratum basale → stratum spinosum → stratum granulosum → stratum corneum

Thick skin layers

Stratum basale → stratum spinosum → stratum granulosum → stratum lucidum → stratum corneum; palms, soles, palmar/plantar sides of fingers/toes

Stratum basale

Deepest layer; attaches to basement membrane via hemidesmosomes; basal stem cells reproduce keratinocytes

Stratum corneum

Superficial layer; 15–30 layers of dead, keratinized cells; protects from abrasion, microbes, heat; lamellar granules waterproof cells

Keratinocyte movement

Move upward from stratum basale → corneum in ~30–40 days; flatten and produce keratin + lipid granules

Stratum granulosum changes

Keratin bundles toughen, envelope proteins form sac, lamellar granules release lipids, cells die → waterproof sacks

Epidermal water barrier

Created by keratinocytes + tight junctions + lamellar granules; retains body water; water-resistant not waterproof

Insensible perspiration

Evaporation of water from interstitial fluid; ~500 mL/day; invisible, unavoidable

Sensible perspiration (diaphoresis)

Sweat visible; cools body via evaporation

Melanocytes

8% of epidermal cells; located in stratum basale; produce melanin

Melanin

Protein produced by melanocytes; transferred to keratinocytes; protects nuclei from UV

Melanoma

Cancer of melanocytes

Skin color differences

Reflect melanocyte activity, melanin distribution in keratinocytes, and rate of melanin breakdown

Albinism

Normal number/distribution of melanocytes, but no melanin production → white skin/hair, pale eyes

UV exposure effect

Increases melanocyte activity; peak response ~10 days after exposure

Carotene

Orange-yellow pigment from diet (carrots, squash, sweet potatoes); stored in adipose tissue and stratum corneum; converted to vitamin A

Vitamin A

Essential for epithelial tissue integrity and photoreceptor pigments in eyes

Hemoglobin

Red/pink pigment in RBCs; carries oxygen and carbon dioxide; affects skin redness with blood flow

Dermis

Deep layer of skin; 0.2–4 mm thick; loose + dense irregular connective tissue; contains structures and cells

Dermis zones

Papillary layer, reticular layer

Papillary layer

Loose connective tissue, capillaries, lymphatic vessels, sensory neurons

Dermal papillae

Form epidermal ridges (interlock with epidermis); friction ridges on fingertips, palms, soles; bring nerve fibers closer to surface

Reticular layer

Dense irregular connective tissue; collagen and elastic fibers; contains dermal structures; small adipocyte clusters; stretch marks form here

Subcutaneous tissue (hypodermis)

Loose connective tissue + adipose tissue; stabilizes skin position, allows free movement, acts as blood reservoir, insulation, energy reserve, shock absorber

Thermoregulatory role of subcutaneous adipose

Helps conserve or release heat depending on environment

Hair

Located in follicles; non-living; functions: communication, identification, sexual maturity indication, protection, sensation, insulation

Hair color

Determined by melanin type; influenced by genetics, hormones, environment; white hair = lack of melanin + air bubbles

Arrector pili

Muscle attached to hair; raises hair for insulation or nonverbal communication

Sebaceous glands

Attached to hair follicles; none on palms/soles; secrete sebum onto hair or skin surface

Sebum

Oil; lubricates hair/skin, prevents drying, provides barrier to microbes

Eccrine sweat glands

Most common; smaller, superficial; secrete onto skin; found everywhere except lips, nail beds, genitals, eardrum; water + ions + urea + ammonia + glucose + lactic acid; pH 4–6; dermcidin

Eccrine gland function

Cools skin, excretes water/electrolytes, protects from hazards

Apocrine sweat glands

Located in axilla, groin, areola, beard, anal region; activate at puberty; secrete into hair follicle; eccrine sweat + lipids/proteins; emotional/sexual activation; source of human pheromones

Ceruminous glands

Produce cerumen (ear wax); protect ear canal

Mammary glands

Modified apocrine glands; produce milk; associated with reproductive system

Nails

Accessory structures of skin; composed of keratin; protect tips of fingers/toes; assist in grasping objects

Nail plate

Hard part of nail; rests on nail bed

Nail bed

Underlying epidermis supporting nail plate

Nail matrix

Region of nail growth; contains stem cells for nail production

Tactile (Merkel) cells

Stratum basale; detect light touch; part of tactile epithelial complex with nerve endings

Corpuscles of touch (Meissner’s corpuscles)

Located in dermal papillae; detect fine touch, texture, light pressure; especially in fingertips, lips

Lamellated (Pacinian) corpuscles

Deep dermis or hypodermis; detect deep pressure and vibration

Skin homeostasis

Protects against trauma, infection, UV radiation, water loss; regulates temperature; sensory input; vitamin D synthesis; excretion of wastes

Thermoregulation

Increased blood flow + sweat secretion to cool; reduced blood flow + reduced sweat to conserve heat

Excretion via skin

Sweat removes water, salts, urea, ammonia, uric acid; small amounts of CO2

Absorption through skin

Lipid-soluble substances (steroids, vitamins A, D, E, K), toxins (acetone, arsenic, lead, mercury), poison ivy/oak oils

Vitamin D synthesis

UV + epidermal cells → cholecalciferol (D3); liver converts to calcidiol; kidney converts to calcitriol (active form)

Calcitriol function

Active vitamin D; essential for Ca and P absorption in small intestine

Vitamin D deficiency

Rickets; low Ca absorption; weak, flexible bones; bowed lower limbs

Skin as a multilayered organ

Provides barrier, protection, insulation, sensory reception; allows repair and replacement of damaged layers

Hair

Filament of keratinized cells; located in hair follicles; non-living; provides protection, sensation, insulation, and nonverbal communication

Hair Follicle

Organ that produces hair; surrounds root; extends from epidermis into dermis

Arrector Pili Muscle

Smooth muscle attached to hair follicle; contracts to make hair stand (goosebumps); contributes to thermoregulation

Hair Color

Determined by type and amount of melanin; influenced by genetics, hormones, and environment; white hair = absence of melanin + air bubbles

Sebaceous Glands

Glands attached to hair follicles (except palms and soles); secrete sebum (oil) onto hair/skin; lubricates and protects skin/hair; antibacterial

Sebaceous Follicles

Large sebaceous glands not associated with hair; secrete sebum directly onto skin surface

Sweat Glands

Eccrine and apocrine types; secrete sweat; involved in thermoregulation and excretion

Eccrine Sweat Glands

Most common sweat glands; small, superficial; active throughout life; secrete directly onto skin; found almost everywhere (except lips, nail beds, genitals, eardrum); sweat = water + ions + urea + uric acid + ammonia + amino acids + glucose + lactic acid; pH 4-6; contains dermcidin

Eccrine Gland Function

Cools skin via evaporation, excretes water/electrolytes, protects against microbes (acid mantle, dermcidin)

Apocrine Sweat Glands

Found in axilla, groin, areola, beard, anal region; activate at puberty; secrete into hair follicle; composition = eccrine sweat + lipids/proteins; respond to emotional stress/sexual excitement; source of pheromones

Ceruminous Glands

Ear canal glands; secrete cerumen (earwax); protects ear canal by trapping debris and preventing microbial growth

Mammary Glands

Modified sweat glands in reproductive system; produce milk; composition and function adapted for lactation

Nails

Protect distal digits; made of keratin; consist of nail plate, nail bed, nail matrix; assist in manipulation and sensation

Tactile (Merkel) Cells

Epidermal cells; found in stratum basale; associated with nerve endings (tactile discs); detect light touch and texture

Corpuscle of Touch (Meissner)

Encapsulated sensory receptor; found in dermal papillae of glabrous skin (palms, fingertips, soles); detects fine touch and texture

Lamellated Corpuscle (Pacinian)

Encapsulated sensory receptor; found deep in dermis/subcutaneous tissue; detects pressure and vibration

Homeostasis: Thermoregulation

Skin regulates body temperature via blood flow, sweating, and arrector pili contraction; maintains internal environment

Homeostasis: Excretion

Skin removes water, salts, urea, ammonia, uric acid via sweat; small amounts of CO2 can also be excreted

Homeostasis: Vitamin D Synthesis

UV exposure converts 7-dehydrocholesterol in epidermis to cholecalciferol (vitamin D3); liver converts to calcidiol; kidney converts to calcitriol (active); essential for Ca & P absorption in small intestine