Integumentary System: Skin Layers

• The integumentary system includes skin, hair, nails, sweat glands, and sebaceous (oil) glands.

Layers of the Skin

• The epidermis is the outermost layer.
• The epidermis is made of keratinized stratified squamous epithelium.
• The epidermis is avascular (no blood vessels).
• Thick skin has five epidermal layers.
• The stratum basale is the deepest layer, containing melanocytes and stem cells.
• The stratum spinosum contains prickle cells and provides strength.
• The stratum granulosum begins keratinization.
• The stratum lucidum is found only in thick skin (palms and soles).
• The stratum corneum is the outermost layer, consisting of dead keratinized cells.
• The dermis is the middle layer and is vascular (contains blood vessels).
• The dermis has two layers.
• The papillary layer is loose connective tissue and contains Meissner's corpuscles (touch receptors).
• The reticular layer is dense connective tissue with collagen and elastin.
• The hypodermis (subcutaneous layer) is not part of the skin but anchors it to muscles.
• The hypodermis contains adipose tissue (fat), which absorbs shock and insulates .

Cells of the Epidermis

• Keratinocytes produce keratin, which makes skin waterproof.
• Melanocytes produce melanin, which protects from UV damage.
• Dendritic (Langerhans) cells are part of the immune system.
• Tactile (Merkel) cells are touch receptors.

Skin Color

• Skin color is determined by melanin (brown/yellow/red/black), carotene (yellow-orange), and hemoglobin (red/pink).
• Melanin protects against UV damage.
• Carotene accumulates in the stratum corneum.
• Hemoglobin is in the blood and shows through skin in fair individuals.
• Cyanosis (blue) indicates low oxygen.
• Erythema (redness) indicates fever or inflammation.
• Pallor (pale) indicates anemia or stress.
• Jaundice (yellow) indicates liver disorder.
• Bruises (black & blue) indicate clotted blood under the skin.

Hair & Nails

• Hair protects against heat loss, sunlight, and foreign particles.
• Hair growth is influenced by genetics, hormones, and age.
• Nails are made of hard keratin and protect fingertips.
• Alopecia is hair thinning with age.
• Male pattern baldness is caused by DHT (dihydrotestosterone).
• Hirsutism is excessive hair growth due to high androgens.

Glands of the Skin

• Sweat glands (sudoriferous glands) include eccrine and apocrine glands.
• Eccrine glands are the most numerous and regulate body temperature.
• Apocrine glands are found in armpits and groin and are active at puberty.
• Sebaceous (oil) glands secrete sebum, which keeps skin and hair soft.
• Blocked glands can lead to acne.

Functions of the Skin

• The skin provides protection through chemical, physical, and biological barriers.
• The chemical barrier has antimicrobial properties.
• The physical barrier prevents water loss.
• The biological barrier provides immune defense via Langerhans cells.
• The skin regulates body temperature.
• Sweat glands cool the body.
• Blood vessel constriction conserves heat.
• The skin performs metabolic functions, producing Vitamin D for calcium absorption and detoxifying chemicals.
• The skin provides sensory reception for touch, pressure, pain, and temperature.

Skin Cancer

• The three main types of skin cancer are basal cell carcinoma, squamous cell carcinoma, and melanoma.
• Basal cell carcinoma is the most common and least dangerous.
• Squamous cell carcinoma can spread if untreated.
• Melanoma is the most dangerous and spreads quickly.
• The melanoma ABCD rule includes A (asymmetry), B (border irregularity), C (color variation), and D (diameter >6mm).

Burns

• First-degree burns affect the epidermis only (redness & pain).
• Second-degree burns affect the epidermis and upper dermis (blisters).
• Third-degree burns destroy all skin layers and require skin grafts.
• The rule of nines estimates the percentage of burned skin to assess fluid loss.

Skin Aging

• Skin aging involves thinning skin, loss of elasticity leading to wrinkles, and decreased melanocytes leading to higher cancer risk.
• Prevention includes hydration, nutrition, and sun protection.