Ch 5 - Integumentary System

Integumentary System

The organ system consisting of the skin, sudoriferous (sweat) glands, sebaceous (oil) glands, hairs, nails, and subcutaneous tissue.

Epidermis

The outermost protective shield of the body, consisting of avascular epithelial tissue.

Dermis

The vascular layer underlying the epidermis that makes up the bulk of the skin, composed mostly of dense connective tissue.

Subcutaneous Tissue

Also called the hypodermis or superficial fascia; tissue composed mostly of adipose and some areolar connective tissue that loosely anchors skin to underlying muscles, absorbs shock, and provides insulation.

Keratinocytes

The major cell type of the epidermis that produces fibrous keratin, providing protective properties; millions slough off daily to renew the epidermis every 25 to 45 days.

Melanocytes

Spider-shaped cells located in the deepest epidermis that produce melanin and package it into melanosomes to protect keratinocyte nuclei from UV damage.

Dendritic Cells

Also known as Langerhans cells; star-shaped macrophages patrolling the deep epidermis that ingest foreign substances and act as key activators of the immune system.

Tactile Epithelial Cells

Also known as Merkel cells; sensory receptors for touch located at the epidermal-dermal junction.

Stratum Basale

The deepest layer of the epidermis, firmly attached to the dermis and consisting of a single row of actively mitotic stem cells; also known as stratum germinativum.

Stratum Spinosum

The prickly layer of the epidermis, several cell layers thick, containing keratinocytes with a web-like system of intermediate pre-keratin filaments attached to desmosomes.

Stratum Granulosum

The granular layer of the epidermis, four to six cells thick, where cells flatten, nuclei and organelles disintegrate, and keratinization begins with keratohyaline and lamellar granules.

Stratum Lucidum

The clear layer of the epidermis found only in thick skin, consisting of a thin translucent band of two to three rows of clear, flat, dead keratinocytes superficial to the stratum granulosum.

Stratum Corneum

The horny outer layer of the epidermis, consisting of 20 to 30 rows of flat, anucleated, keratinized dead cells, accounting for three-quarters of epidermal thickness.

Papillary Dermis

The thin, superficial layer of the dermis made of areolar connective tissue with loose collagen and elastic fibers, blood vessels, and dermal papillae.

Dermal Papillae

Fingerlike projections from the superficial region of the dermis into the epidermis that contain capillary loops, free nerve endings, and tactile corpuscles (Meissner's corpuscles).

Friction Ridges

Epidermal ridges lying on top of dermal ridges formed by dermal papillae in thick skin that enhance gripping ability and amplify touch sensations.

Reticular Dermis

The deeper dermal layer making up approximately 80% of dermal thickness, composed of coarse, dense irregular connective tissue with collagen and elastic fibers.

Dermal Vascular Plexus

A network of blood vessels located between the reticular dermis and the subcutaneous tissue.

Cleavage Lines

Externally invisible tension lines in the reticular dermis caused by collagen fiber bundles running parallel to the skin surface; surgical incisions parallel to these lines heal more readily.

Flexure Lines

Dermal folds located at or near joints where the dermis is tightly secured to deeper structures, creating deep creases visible on hands, wrists, fingers, soles, and toes.

Striae

Silvery white scars, commonly called stretch marks, caused by extreme stretching of the skin that results in dermal tearing.

Blisters

Fluid-filled pockets separating the epidermal and dermal layers caused by acute short-term trauma such as burns or repeated friction.

Melanin

The only pigment synthesized directly in the skin by melanocytes; packaged in melanosomes to shield keratinocyte DNA against UV radiation.

Carotene

A yellow to orange pigment most obvious in the palms and soles that accumulates in the stratum corneum and subcutaneous tissue and can be converted to vitamin A.

Cyanosis

A bluish discoloration of the skin caused by low oxygenation of hemoglobin, indicating potential respiratory or cardiovascular issues.

Erythema

Redness of the skin caused by conditions such as embarrassment, fever, inflammation, or allergies.

Jaundice

A yellowing of the skin that serves as a clinical sign of liver disorders.

Hematomas

Red, purple, green, or yellow skin markings, commonly known as bruises, resulting from blood leaking from damaged blood vessels beneath the skin.

Skin Color Determination

The result of relative amounts and combinations of three pigments: melanin (synthesized in skin by melanocytes), carotene (ingested yellow-orange pigment), and oxygenated hemoglobin (in dermal blood vessels).

Hair (Pili)

Flexible strands of dead, keratinized cells produced by hair follicles.

Hard Keratin

Tougher and more durable type of keratin found in hair and nails whose cells do not flake off.

Soft Keratin

Type of keratin found in the skin.

Hair Root

The portion of hair within the scalp where keratinization is still going on.

Hair Shaft

The portion of hair that extends above the scalp where keratinization is complete.

Medulla

The central core of the hair shaft consisting of large cells and air spaces.

Cortex

Several layers of flattened cells surrounding the medulla in the hair shaft.

Cuticle (Hair Shaft)

The outer layer of the hair shaft consisting of overlapping layers of single cells.

Pheomelanin

An additional pigment found in red hair.

Hair Follicle

Structure extending from the epidermal surface into the dermis (and sometimes subcutaneous tissue) that produces hair.

Hair Bulb

The expanded area at the deep end of a hair follicle.

Hair Follicle Receptor (Root Hair Plexus)

Sensory nerve endings that wrap around the hair bulb, making hair act as a sensory touch receptor.

Peripheral Connective Tissue Sheath (Fibrous Sheath)

The external layer of the hair follicle wall derived from the dermis.

Glassy Membrane

The basement membrane of the hair follicle epithelium.

Epithelial Root Sheath

The thickest layer of the hair follicle wall derived from epidermis, comprising an external root sheath and internal root sheath.

Hair Papilla

Dermal tissue containing a knot of capillaries located at the base of the follicle that supplies nutrients to growing hair.

Hair Matrix

The actively dividing area of the hair bulb that produces hair cells and pushes older cells upward.

Arrector Pili

A small band of smooth muscle attached to the hair follicle that is responsible for causing goose bumps.

Vellus Hair

Pale, fine body hair characteristic of children and adult females.

Terminal Hair

Coarse, long hair found on the scalp and eyebrows, and appearing at puberty in axillary and pubic regions of both sexes as well as the face and neck of males.

Male Pattern Baldness

A genetically determined, male sex hormone-influenced condition in which hair follicles respond to androgens with decreasing growth cycles.

Nails

Scale-like modifications of the epidermis containing hard keratin that act as a protective cover for the distal, dorsal surface of fingers and toes.

Nail Plate (Nail Body)

The visible attached portion of the nail.

Nail Bed

The layer of epidermis situated underneath the keratinized nail plate.

Nail Matrix

The thickened portion of the nail bed responsible for nail growth.

Eponychium (Cuticle)

The proximal nail fold that projects onto the surface of the nail body.

Hyponychium

The region underneath the free edge of the nail plate that accumulates dirt.

Lunule

The white, crescent-shaped region at the base of the nail body representing the thickened nail matrix.

Koilonychia

An outward concavity of the nail (also called spoon nail) that may signal an iron deficiency.

Beau's Lines

Horizontal lines across nails that may indicate severe illnesses such as uncontrolled diabetes, heart attack, or cancer chemotherapy.

Sudoriferous Glands

Sweat glands that function in controlling body temperature; present on all skin surfaces except nipples and parts of external genitalia.

Eccrine Sweat Glands

The most numerous sweat glands, abundant on palms, soles, and forehead, whose ducts connect to pores on the skin surface to release sweat for thermoregulation.

Apocrine Sweat Glands

Large sweat glands located mostly in axillary and anogenital areas that secrete viscous milky or yellowish sweat containing fatty substances and proteins into hair follicles.

Ceruminous Glands

Modified apocrine sweat glands located in the lining of the external ear canal that secrete cerumen (earwax).

Mammary Glands

Modified apocrine sweat glands specialized to secrete milk.

Sebaceous Glands

Widely distributed holocrine oil glands (absent on palms and soles) that secrete sebum into hair follicles.

Sebum

An oily secretion produced by sebaceous glands that possesses bactericidal properties and softens hair and skin.

Chemical Barriers of Skin

Chemical secretions including sweat (antimicrobial proteins), sebum, defensins, the acidic acid mantle (slows bacterial growth), and melanin (shields DNA from UV radiation).

Physical Barriers of Skin

Flat, dead, keratinized cells in the stratum corneum surrounded by water-resistant glycolipids that block water and most water-soluble substances.

Biological Barriers of Skin

Active immune cells including dendritic cells in the epidermis and macrophages in the dermis that engulf foreign antigens and activate white blood cells.

Cutaneous Sensory Receptors

Exteroceptors including tactile (Meissner's) corpuscles for touch, lamellar (Pacinian) corpuscles for deep pressure, hair follicle receptors for hair movement, and free nerve endings for pain.

Metabolic Functions of Skin

Synthesizes vitamin D precursors in response to sunlight, disarms potential carcinogens via keratinocyte enzymes, converts cortisone into active hydrocortisone, and synthesizes collagenase.

Skin Blood Reservoir

The dermal vascular network holds up to $5\%$ of total blood volume, which can be constricted to shunt blood to other active body organs.

Excretory Function of Skin

Removes nitrogenous waste products (ammonia, urea, uric acid) and leads to sodium chloride and water loss through sweat secretion.

Basal Cell Carcinoma

Least malignant and most common skin cancer ($80\%$ of cases) where stratum basale cells proliferate and invade dermis and subcutaneous tissue; cured by surgical excision in $99\%$ of cases.

Squamous Cell Carcinoma

Second most common skin cancer involving stratum spinosum keratinocytes; presents as a scaly reddened papule and can metastasize if left untreated.

Melanoma

Most dangerous skin cancer originating from melanocytes ($1\%$ of cases); highly metastatic and resistant to standard chemotherapy.

ABCD(E) Rule for Early Skin Cancer Detection

A = Asymmetry; B = Border Irregularity; C = Color variation; D = Diameter greater than $6\,\text{mm}$; E = Evolution/Evolving over time.

Rule of Nines

Divides body surface area into $11$ sections of $9\%$ each (plus perineum at $1\%$) to evaluate burn surface area and estimate volume of fluid loss.

First-Degree Burns

Partial-thickness burn affecting only the epidermis, manifesting as localized redness, edema (swelling), and pain.

Second-Degree Burns

Partial-thickness burn causing epidermal and upper dermal damage, characterized by blister formation, swelling, and pain.

Third-Degree Burns

Full-thickness burn involving the entire skin depth; skin appears gray-white, cherry red, or blackened, with little to no pain due to destroyed nerve endings.

Critical Burn Thresholds

Burns are classified as critical if > $25\%$ of body surface has 2nd-degree burns, > $10\%$ has 3rd-degree burns, or 3rd-degree burns are on the face, hands, or feet.

UVA vs. UVB Rays

UVA rays are aging rays that damage deep structural components; UVB rays are burning rays that damage superficial DNA and cause sunburns.

The primary physiological functions of skin

• Protection

• Body temperature regulation

• Cutaneous sensations

• Metabolic functions

• Blood reservoir

• Excretion

Physiological Effects of Skin Aging

Aging causes slowed epidermal renewal, decreased subcutaneous fat and elasticity (leading to cold intolerance and wrinkles), reduced melanocytes and dendritic cells (increasing skin cancer risk), and hair follicle atrophy.