Integumentary System and Body Membranes

Sebaceous Glands

Exocrine oil glands throughout the skin except palms and soles, usually emptying into hair follicles and starting when you are a teen to secrete sebum that lubricates, waterproofs, and protects skin and hair.

Sebum

An oily product of sebaceous glands consisting of lipids and fragmented cells that softens skin, keeps hair flexible, and contains bacteria-killing chemicals.

Whitehead

A white skin blemish that forms when a sebaceous gland's duct is blocked by trapped sebum.

Blackhead

A darkened lesion formed when sebum gets trapped within a blocked duct oxidizes, dries, and turns black.

Acne

Inflammation caused by hair follicles and sebaceous glands becoming blocked with oil and dead skin cells, leading to pimples and potential scarring.

Seborrhea

A condition caused by overactivity of the sebaceous glands, commonly referred to as cradle cap in infants.

Eccrine Sweat Glands

Thermoregulation, cools body in heat or exercise. Opens onto skin via pores. Over 2.5 million widespread, densest palms, soles, forehead. Clear, watery, salty, pH 4 to 6 fights bacteria. Odorless, resists bacterial breakdown. Active from birth.

Apocrine Sweat Glands

Responds to stress, hormones. Opens into hair follicles. Concentrated in armpits, groin, scalp. Thick, milky, yellowish, rich in proteins, fats. Body odor via bacterial breakdown. Active at puberty.

Cuticle (Hair)

The outermost protective layer of the hair shaft, consisting of single-layered overlapping dead keratin cells arranged like roof shingles that prevent hair matting.

Cortex (Hair)

The thick intermediate layer of the hair shaft surrounding the medulla hair that contains structural material providing hair 90% of mass and strength.

Medulla (Hair)

The central core and innermost region of the hair shaft.

Hair Shaft Layers

The three concentric cylindrical regions of nonliving keratinized protein forming a hair: the outermost cuticle, intermediate cortex, and central core medulla.

Hair Matrix

The cellular growth zone located in the hair bulb at the base of the follicle where stem cells actively divide to produce hair.

Hair Bulb

The enlarged, living base of a hair follicle located deep within the dermis layer of the skin. Command center and only part of the follicle that actively manufactures a strand of hair.

Arrector Pili Muscle

Small bands of smooth muscle cells connecting the hair follicle to dermal tissue that contract in response to cold or fright, raising hairs to produce goose bumps.

Nail Structure

A scalelike modification of the epidermis consisting of a free edge, visible body, embedded root, underlying nail bed, and a proximal growth matrix.

Nail Matrix

The thickened proximal section of the stratum basale in the nail bed responsible for continuous cellular division and nail growth.

Lunule

The white crescent-shaped proximal region of the nail body lying over the thickened nail matrix.

Cyanosis

A condition characterized by a bluish discoloration of the skin and nail beds resulting from low oxygen saturation in the blood.

Burn

Tissue damage and cellular destruction inflicted by intense heat, cold, electricity, UV or chemical agents.

Circulatory Shock

A life-threatening complication of severe burns caused by excessive fluid loss, dehydration, and low blood volume leading to inadequate circulation.

First-Degree Burn

A burn involving only the epidermis, characterized by redness, swelling, and temporary discomfort, which generally heals in $2\text{–}3\text{ days}$ without scarring.

Second-Degree Burn

A burn that damages the epidermis and upper dermis, marked by pain, redness, and blisters, where regeneration occurs without scarring if infection is prevented.

Third-Degree Burn

A full-thickness burn destroying the entire epidermis and dermis, presenting a blanched or blackened appearance, and lacking initial pain due to destroyed nerve endings.

Neoplasm

An abnormal cellular mass resulting from uncontrolled growth, classified as either benign (non-spreading) or malignant (cancerous).

Metastasis

The spreading of malignant cancer cells from their site of origin to distant body structures via lymphatic vessels or the bloodstream.

Basal Cell Carcinoma

The most common and least malignant skin cancer, arising from cells of the stratum basale that invade the dermis and hypodermis, cured by surgical excision in most cases.

Squamous Cell Carcinoma

A skin malignancy originating in the stratum spinosum that appears as a scaly, reddened papule and can metastasize rapidly to regional lymph nodes if untreated.

Melanoma

An aggressive cancer of melanocytes, often appearing as a spreading asymmetrical brown-to-black lesion arising spontaneously or from a preexisting mole.

ABCD Rule

A mnemonic clinical guide for identifying melanoma based on Asymmetry, Border irregularity, Color variation, and Diameter

Carotene

An orange-yellow pigment stored in epidermal cells and fatty tissues that can be converted into vitamin A to support eye health.

Melanin

A yellow-brown to black pigment produced by melanocytes and packaged into intracellular vesicles to shield epidermal DNA against UV radiation.

Albinism

An inherited condition in which individuals have normal numbers of melanocytes that lack the physiological ability to synthesize melanin.

Friction Ridges

Raised structural contours on fingertip surfaces formed by epidermal and dermal interactions that increase friction, improve grip, and heighten tactile sensitivity.

Fingerprint Patterns

The three primary epidermal ridge arrangements transferred onto surfaces by sebum and sweat: loops, whorls, and arches.

Layers of the Skin

The epidermis, the dermis, and the hypodermis.

Papillary Layer

The superficial region of the dermis composed of loose connective tissue containing capillaries and nerve fibers, papillae project into the epidermis to provide nutrition and attachment, above the reticular layer and deeper hypodermis (subcutaneous layer).

Reticular Layer

The deeper, thicker dermal region consisting of dense irregular connective tissue containing collagen fibers for tensile resistance and elastic fibers for stretch and recoil.

Hypodermis

The subcutaneous layer deep to the dermis, composed of loose connective and adipose tissue, which cushions organs, insulates against heat loss, stores energy, and anchors the skin.

Mucous Membrane

A moist membrane of simple epithelia and loose connective tissue its functions are absorption and secretion and lines the digestive, respiratory, reproductive, and urinary tracts.

Serous Membrane

A paired parietal and visceral membrane of simple epithelium and loose connective tissue lining sealed cavities around the lungs, heart, and abdomen, secreting serous fluid to cut friction.

Parietal Layer

The outer layer of serous membrane that lines the wall of the body cavity.

Visceral Layer

The inner layer of serous membrane that directly covers and adheres to an organ.

Pericardium

The serous membrane structure enclosing the heart, consisting of an outer parietal layer, an inner visceral layer, and a fluid-filled cavity.

Cutaneous Membrane

The integumentary which has the epidermis and dermis and protects internal tissues from physical damage, pathogens, and water loss while helping regulate body temperature.

Synovial Membrane

A connective tissue membrane with no epithelial cells that lines the fibrous capsules of articulating joints and secretes lubricating synovial fluid.

Epidermis

The avascular, outermost protective epithelial envelope of the skin composed primarily of keratinized stratified squamous cells organized into four or five strata, that blocks pathogens and UV rays, retains moisture, and senses touch.

Stratum Basale

The deepest single layer of columnar or cuboidal germinative stem cells resting on the basement membrane, actively dividing to renew the epidermis and housing melanocytes.

Stratum Spinosum

The epidermal stratum immediately superficial to the stratum basale, composed of several cell layers of maturing keratinocytes connected by desmosomes.

Stratum Granulosum

The epidermal layer where cells cease division, begin flattening, and produce massive quantities of the water-resistant fibrous protein keratin.

Stratum Lucidum

A clear, thin, translucent layer of flattened, keratin-packed dead cells found exclusively in thick skin on the palms of hands and soles of feet.

Stratum Corneum

The outermost stratum composed of $20\text{–}30$ layers of dead, flattened, fully keratinized cells linked by desmosomes that shed continuously in large sheets.

Keratin

An exceptionally durable, water-resistant fibrous structural protein synthesized by keratinocytes that forms the basis of hair, nails, calluses, and epidermal armor.

Vitiligo

Autoimmune loss of melanocytes causing patchy white areas of skin.

Psoriasis

Chronic autoimmune condition causing overproduction of skin cells, resulting in thick, red, silvery-scaled patches.

Impetigo

Contagious bacterial skin infection (usually Staphylococcus or Streptococcus) causing pink, water-filled lesions that develop a yellow crust.

Athlete's Foot (Tinea pedis)

Contagious fungal infection causing itchy, red, peeling skin between the toes.

Peritoneum

Lines the abdominal cavity and covers abdominal organs.

Pleura

Lines the thoracic cavity walls and covers the lungs.

Critical Burn Criteria

Burns are considered critical if over 25% of the body has second-degree burns, over 10% of the body has third-degree burns, or there are third-degree burns on the face, hands, or feet.

Major Functions of the Skin

Protects against mechanical, chemical, bacterial, and UV damage; regulates body temperature; excretes urea and salts; synthesizes vitamin D; and houses cutaneous sensory receptors.

Dermis

The middle connective tissue layer of the skin (papillary and reticular layers) between the epidermis and hypodermis, containing blood vessels, lymphatic vessels, nerve fibers, sensory receptors, hair follicles, sweat glands, sebaceous glands, and arrector pili muscles to provide strength and elasticity, regulate temperature, nourish and lubricate the skin, and sense touch and pain.

Membrane Classifications

Cutaneous, mucous, and serous membranes are epithelial membranes, whereas synovial membranes are connective tissue membranes.

Benign vs. Malignant Skin Masses

Benign masses are non-cancerous and remain localized without spreading, while malignant masses are cancerous and can metastasize (spread) to distant body parts.

A - Asymmetry

The two halves of a mole or pigmented lesion do not match in shape.

B - Border Irregularity

The edges of a lesion are ragged, notched, blurred, or scalloped rather than smooth and even.

C - Color Variation

A mole contains multiple shades (such as tan, brown, black, red, white, or blue) instead of one uniform color.

D - Diameter

A pigmented lesion is larger than 6 mm across (roughly the size of a pencil eraser).

E - Evolving

A mole is changing in size, shape, color, or elevation over time, or developing new symptoms like bleeding or itching.

Aging

Skin becomes thinner and drier, sagging and wrinkling occur, hair thins and grays, immune sensitivity drops, vitamin D3 production declines, heat loss decreases, and skin repairs slow down.

Why Burns Are Dangerous

Severe burns destroy the protective skin barrier, leading to massive fluid loss (proteins and electrolytes), dehydration, electrolyte imbalance, and life-threatening circulatory shock from low blood volume.

Sweat Gland

Coiled tubular epithelial glands in dermis opening onto skin surface or hair follicles, comprising eccrine and apocrine types that secrete watery or organic sweat for thermoregulation, waste excretion, and protection.

Hair and Hair Follicles

Accessory skin structures extending epidermis to dermis, dead keratinized epithelial cells forming shaft and root inside epithelial-connective follicle with vascular papilla, matrix, sebaceous glands, nerves, arrector pili for protection, touch, warmth.

Root

Portion of hair embedded beneath skin surface inside follicle, composed of keratinized epithelial cells growing from dividing hair matrix to anchor hair.

Hair Shaft

Visible portion of hair projecting above skin surface, composed of dead keratinized epithelial cells arranged in medulla, cortex, and cuticle layers for protection, light touch sensation, and heat retention.

Sweat Gland Duct

Narrow stratified cuboidal epithelial tube extending from coiled secretory portion in dermis to skin surface pore or hair follicle, transporting and modifying sweat by reabsorbing sodium and chloride ions.

Sweat Gland Pore

Tiny funnel-shaped epidermal opening at skin surface connected to coiled eccrine sweat gland duct, releasing sweat onto epidermis to cool body through evaporation and excrete wastes.

Erector Pilius Muscle

Small bundle of smooth muscle cells in dermis extending from papillary layer to hair follicle connective tissue sheath, contracting involuntarily in response to cold or emotion to pull hair upright, trap warmth, and squeeze sebum from sebaceous glands.

Blood Vessels

Network of elastic and muscular tubes coursing through dermis and hypodermis, transporting oxygen, nutrients, and immune cells while removing metabolic wastes and regulating body temperature through blood flow changes

Exocrine Sweat Gland

Glands that produce and discharge sweat through ducts onto the skin surface or into hair follicles. Two main types are eccrine and apocrine sweat glands.

Cancer

Abnormal mass of mutated cells forming malignant tumors that grow uncontrollably within skin layers due to DNA damage from UV radiation or carcinogens, invading surrounding tissues and disrupting normal barrier, sensory, and regulatory skin functions.