Integumentary System

Skin (Cutaneous Membrane)

Definition: The body's outer covering made of epithelial and connective tissue.

Importance: Protects internal organs, regulates temperature, and provides sensory input.

Function: Acts as a barrier, regulates heat, synthesizes vitamin D, and detects stimuli.

Location: Covers the entire body.

Quick Tip: Skin is your first line of defense — treat it gently and moisturize regularly.

Thin Skin

Definition: Type of skin that grows hair and lacks dermal ridges.

Importance: Provides flexibility and sensory input.

Function: Covers most of the body and allows hair growth.

Location: Found everywhere except palms and soles.

Quick Tip: If it grows hair, it’s thin skin.

Thick Skin

Definition: Hairless skin with dermal ridges designed for friction resistance.

Importance: Enhances grip and protects high-friction areas.

Function: Prevents damage in areas of frequent contact.

Location: Palms of hands and soles of feet.

Quick Tip: Fingerprints come from thick skin’s dermal ridges.

Epidermis

Definition: The outermost layer of skin made of stratified squamous epithelial tissue.

Importance: Provides waterproof protection and regenerates quickly.

Function: Shields against dehydration, UV rays, and pathogens.

Location: Superficial layer of skin. Quick Tip: The epidermis is avascular — it gets nutrients from the dermis below.

Stratum Corneum

Definition: Top layer of epidermis made of dead keratinized cells.

Importance: Acts as a tough, protective barrier.

Function: Prevents water loss and blocks pathogens.

Location: Outermost layer of epidermis.

Quick Tip: This is the layer that flakes off when your skin peels.

Stratum Lucidum

Definition: Clear layer found only in thick skin.

Importance: Adds extra protection in high-friction areas.

Function: Enhances durability of thick skin.

• ABSENT IN THIN SKIN

Location: Palms and soles. Quick Tip: If it’s not on your palm or sole, it’s not lucidum

Surface Film

• Definition: A thin layer of sweat, oil, and dead cells on the skin.

• Function: Protects, hydrates, and prevents infection.

• Location: On the outermost skin layer (stratum corneum).

• Importance: Keeps skin healthy and balanced.

• Quick Tip: “Sweat + oil = skin shield” It’s your body’s natural armor—keeping moisture in and germs out.

Stratum Granulosum

Definition: Layer where cells begin to die and keratinize.

Importance: Prepares cells for protective outer layer.

Function: Transitions living cells to dead protective cells.

Location: Middle layer of epidermis.

Quick Tip: This is the skin’s “prep zone” before cells die.

Stratum Spinosum

Definition: Layer where cells are held together by desmosomes.

Importance: Provides structural integrity.

Function: Supports skin strength and some cell division.

Location: Just above the stratum basale.

Quick Tip: Desmosomes = skin’s Velcro.

Stratum Basale

Definition: Deepest layer of epidermis with high mitotic activity.

Importance: Generates new skin cells.

Function: Replaces dead cells with new ones.

Location: Base of epidermis.

Quick Tip: Skin regeneration starts here.

Stratum Germinativum

Definition: Combined term for stratum basale and stratum spinosum.

Importance: Site of active cell division.

Function: Produces new epidermal cells.

Location: Lower layers of epidermis.

Quick Tip: Germinativum = growth zone.

5 Layer Epididermis (Superifical to deep)

• Stratum corneum

  • Composed of dead, flattened keratinocytes.

  • Acts as a tough, protective barrier.

• Stratum lucidum ✨ (only in thick skin like palms and soles)

  • Thin, clear layer of dead cells.

  • Adds extra protection and thickness.

• Stratum granulosum

  • Cells begin to die and accumulate keratohyalin granules.

  • Helps waterproof the skin.

• Stratum spinosum 🕸

  • Contains living keratinocytes connected by desmosomes.

  • Provides strength and flexibility.

• Stratum basale (germinativum) 🌱

  • Deepest layer, where cell division occurs.

  • Contains melanocytes and stem cells for regeneration.

• (Come, lets, get, sun, burnt)

Keratinize

• Definition: When skin cells produce keratin, a tough protein, and become part of the outer protective layer.

• Function: Makes skin strong, water-resistant, and protective.

• Location: Happens in the epidermis, especially in the stratum corneum.

• Importance: Shields your body from germs, injury, and dehydration.

• Quick Tip: Think of it like “armor-building”—your skin cells toughen up as they rise to the surface

Keratinocytes

Definition: Cells that produce keratin.

Importance: Waterproofs and protects skin.

Function: Form the bulk of the epidermis.

Location: Throughout epidermis.

Quick Tip: Dry skin often means keratinocytes need support.

Melanocytes

Definition: Cells that produce melanin pigment.

Importance: Protects DNA from UV damage.

Function: Absorbs UV light to prevent mutations.

Location: Stratum basale.

Quick Tip: More sun = more melanin = darker skin.

Dendritic Cells

Definition: Immune cells that respond to skin damage.

Importance: First responders to infection.

Function: Trigger immune response.

Location: Epidermis.

Quick Tip: Scratches activate these defenders.

Merkel Cells

Definition: Sensory receptors for touch.

Importance: Detect light pressure.

Function: Relay tactile information.

Location: Stratum basale.

Quick Tip: Sensitive areas like fingertips have more Merkel cells.

Dermoepidermal Junction

Definition: Basement membrane between epidermis and dermis.

Importance: Anchors skin layers together.

Function: Prevents separation and supports skin structure.

Location: Between epidermis and dermis.

Quick Tip: Blisters form when this junction is disrupted.

Dermis

Definition: Thicker, vascular layer beneath epidermis.

Importance: Supports skin with blood supply and strength.

Function: Nourishes epidermis and provides elasticity.

Location: Beneath epidermis.

Quick Tip: Scar tissue forms here due to low mitosis.

Papillary Layer

• Definition: The upper layer of the dermis, just beneath the epidermis.

• Function: Supplies nutrients to the skin, supports temperature regulation, and helps with touch sensation.

• Location: Directly under the epidermis, part of the dermis.

• Importance: Contains capillaries and nerve endings—key for feeling and skin health.

• Quick Tip: Think of it as the “support crew” for your skin’s surface—feeding it and helping you feel touch

Reticular Layer

• Definition: The deeper, thicker part of the dermis.

• Function: Provides strength, elasticity, and houses structures like sweat glands, hair follicles, and blood vessels.

• Location: Beneath the papillary layer, part of the dermis.

• Importance: Supports skin structure and anchors important skin functions.

• Quick Tip: Think of it as the “foundation layer”—strong, stretchy, and full of working parts.

Hypodermis (Subcutaneous Layer)

Definition: Fat-rich layer beneath dermis.

Importance: Insulates and cushions the body.

Function: Stores energy and regulates temperature.

Location: Deepest skin layer.

Quick Tip: Pinch your skin — the squishy part is hypodermis.

Hair

Definition: Keratinized shaft growing from follicle.

Importance: Protects and senses environment.

Function: Detects touch and regulates temperature.

Location: Thin skin areas.

Quick Tip: Goosebumps = arrector pili muscle action.

Nails

Definition: Keratin plates from germinal matrix.

Importance: Protects fingertips and aids precision.

Function: Enhances fine motor skills.

Location: Ends of fingers and toes.

Quick Tip: Cuticle protects nail root from infection.

Eccrine Sweat Glands

Definition: Sweat glands that regulate temperature.

Importance: Prevents overheating.

Function: Secrete sweat directly to skin surface.

Location: All over body.

Quick Tip: Active during exercise or heat.

Apocrine Sweat Glands

Definition: Stress-related sweat glands.

Importance: May release pheromones.

Function: Secrete sweat through hair follicles.

Location: Armpits and groin.

Quick Tip: Start working at puberty.

Sebaceous Glands

Definition: Oil glands that secrete sebum.

Importance: Lubricates and protects skin and hair.

Function: Moisturizes and prevents drying.

Location: Near hair follicles.

Quick Tip: Overactive glands = acne risk.

First Degree Burn

• Definition: A mild burn affecting only the outer layer of skin (epidermis).

• Symptoms: Redness, pain, and slight swelling—no blisters.

• Location: Can happen anywhere on the skin, often from sunburn or brief contact with heat.

• Importance: Usually heals in a few days without scarring; still needs care to prevent infection.

• Quick Tip: Cool the area with water (not ice), keep it clean, and moisturize gently.

Second Degree Burn

• Definition: A burn that affects both the epidermis and part of the dermis.

• Symptoms: Redness, pain, swelling, and blisters.

• Location: Can occur anywhere on the skin from hot liquids, flames, or chemicals.

• Importance: More serious than first-degree; may scar and needs proper care to heal.

• Quick Tip: Cool gently with water, cover with a clean cloth—don’t pop blisters

Third Degree Burn

• Definition: A severe burn that damages all layers of skin—epidermis, dermis, and sometimes deeper tissues.

• Symptoms: Skin may look white, black, or leathery; no pain in the area due to nerve damage.

• Location: Can affect any body part exposed to intense heat, chemicals, or electricity.

• Importance: Requires urgent medical care; healing is slow and often needs skin grafts.

• Quick Tip: Never treat this at home—call emergency services immediately.

Fourth Degree Burn

• Definition: A burn that goes through all skin layers and into muscle, bone, or deeper tissues.

• Symptoms: Charred skin, exposed tissue, no pain due to complete nerve destruction.

• Location: Often from prolonged exposure to fire, electricity, or chemicals.

• Importance: Life-threatening; requires emergency care, surgery, and often amputation or grafting.

• Quick Tip: This is a medical emergency—call 911 immediately and avoid touching or treating the area

Scar

• Definition: A mark left on the skin after healing from a wound or injury.

• Function: Protects the repaired area with collagen, but lacks full strength and flexibility.

• Location: Can form anywhere the skin or tissue was damaged.

• Importance: Shows where healing occurred; may affect appearance or movement depending on depth.

• Quick Tip: Keep healing skin moisturized and protected from sun to reduce scarring.

Immune System

• Definition: Your body’s defense network against germs and disease.

• Function: Detects, attacks, and remembers harmful invaders.

• Location: Found in blood, lymph nodes, bone marrow, and more.

• Importance: Keeps you healthy and heals damage.

• Quick Tip: Sleep, eat well, and manage stress to stay strong.

First line of defense

Definition: Physical barriers like skin and mucous membranes.

Importance: Prevents pathogen entry.

Function: Blocks invaders before they enter.

Location: Body surfaces.

Quick Tip: Washing hands strengthens this line.

Second line of defense

Definition: Non-specific immune cells like neutrophils.

Importance: Attacks invaders inside the body.

Function: Causes inflammation and fever.

Location: Bloodstream.

Quick Tip: Fever = immune system in action.

Third Line of Defense

Definition: Specific immune cells (T and B lymphocytes).

Importance: Targets invaders and builds memory.

Function: Produces antibodies and long-term