Biological Function and Structure of the Integumentary System

Acts as a barrier to protect the body from environmental factors
Prevents mechanical impact, extreme temperatures, and harmful microorganisms
Reduces dehydration while allowing necessary physiological water evaporation
Works with sebaceous glands to synthesize hydrolipids for skin health
Responsible for sensory functions such as pressure, vibration, and tactile sensations.

Components: Skin (largest organ), hair, nails, and cutaneous glands
Functions: Major role in physical exams and most treated organ system in medicine
Dermatology: The study and treatment of the integumentary system.

Skin Layers:
- Epidermis: Stratified squamous epithelium, contains dead keratinized cells, avascular (nourished by diffusion)
- Dermis: Deeper connective tissue layer, rich in blood vessels, composed mostly of collagen
- Hypodermis: Adipose tissue layer, supports skin structure and serves as an energy reservoir

Resistance to Trauma and Infection:
- Features keratin and antimicrobial peptides (dermcidin, defensins)
- Acid mantle protects against harmful substances
Vitamin D Synthesis:
- Skin completes the first step; liver and kidneys finalize the process
Sensation:
- Contains receptors for temperature, touch, and pain.
Thermoregulation:
- Adjusts blood flow through vasoconstriction/dilation and perspiration
Nonverbal Communication:
- Facial expressions contribute to social interaction and self-image

Cell Types:
- Stem Cells: Undifferentiated cells forming keratinocytes (location: stratum basale)
- Keratinocytes: Majority, produce keratin.
- Melanocytes: Produce melanin to protect DNA from UV radiation.
- Dendritic Cells: Immune role by guarding against pathogens.
- Tactile Cells: Associated with nerve fibers to sense touch.
Strata of the Epidermis:
- Stratum Basale: Bottom layer, includes stem cells.
- Stratum Spinosum: Spiny appearance due to desmosomes, contains some dendritic cells.
- Stratum Granulosum: Contains keratohyalin granules which bind keratin; cells begin to degenerate.
- Stratum Lucidum: Present only in thick skin, provides an additional barrier.
- Stratum Corneum: Outermost layer, composed of dead cells that prevent water loss and resist abrasion.

Mitosis: Occurs in the deeper layers, newer cells push older cells upwards.
Migration: Takes 30-40 days to migrate to surface, where they exfoliate.
Keratinization: Upon reaching the surface, keratinocytes become keratinized and die.

Structure: Two layers:
- Papillary Layer: Upper layer allowing leukocyte mobility, rich vascular supply
- Reticular Layer: Dense irregular connective tissue, provides strength and elasticity.
Functions: Houses hair follicles, sebaceous, sweat glands, and sensory receptors.

Composition: More adipose and areolar tissue than the dermis, serves as cushioning and energy reservoir.
Characteristics: Thicker in women, varies in elderly and infants.

Melanin Production:
- Darker skin has increased melanin production and slower breakdown.
Influencing Factors: Hemoglobin (reddish hue), and carotene (yellow tint).

Hair:
- Composed of dead keratinized cells, three hair types (lanugo, vellus, terminal) based on thickness and pigmentation.
Nails: Derived from stratum corneum, enhance sensory abilities and protect fingertips.

Sebaceous Glands: Produce sebum to moisturize skin.
Sweat Glands:
- Apocrine: Active during puberty, located in specific areas, may secrete pheromones.
- Eccrine: Most common, responsible for thermoregulation through perspiration.

Basal Cell Carcinoma: Most common, originates from stratum basale, low metastasis potential.
Squamous Cell Carcinoma: Arises from keratinocytes, has higher potential for metastasis.
Malignant Melanoma: Most dangerous, can be fatal if metastasizes.

First Degree: Epidermis only, red and painful, heals within days.
Second Degree: Involves part of the dermis, may blister, healing varies.
Third Degree: Full thickness, potentially requiring grafts and extensive care.