Overview
The integumentary system consists of skin (the body's largest organ) and associated structures. It maintains homeostasis, protects internal organs from damage and pathogens, produces vitamin D, and provides sensory functions.
Integumentary System Functions
- Maintains internal body temperature and fluid balance for homeostasis
- Acts as physical barrier protecting internal structures and organs from damage
- Prevents invasion of pathogens like bacteria and fungi
- Produces vitamin D necessary for body functions
- Provides sensory functions allowing awareness of external stimuli like touch
Cell Types in the Epidermis
- Keratinocytes produce keratin, a protein making cells water-resistant and tough
- Keratinocytes form at bottom epidermis layer and push upward to surface
- Cornified cells are hardened, flattened, dead keratinocytes full of keratin without organelles
- Melanocytes produce melanin pigment creating skin colors and protecting from UV rays
- Merkel cells work with nerves to provide sense of touch (exact function uncertain)
Epidermal Layers
The epidermis has five layers from outer to inner (mnemonic: "Can lemurs get some bamboo?"):
| Layer | Characteristics | Cell Type | Notes |
|---|
| Stratum corneum | Outermost layer | Dead cornified cells | Continuously shed and replaced from below |
| Stratum lucidum | Present in thick skin only | Dead cornified cells | Found on palms and foot soles; transparent appearance |
| Stratum granulosum | Flattening keratinocytes | Living keratinocytes with granules | Cells lose organelles becoming cornified |
| Stratum spinosum | Multiple keratinocyte layers | Keratinocytes and macrophage-like cells | Appears spiny under microscope when stained |
| Stratum basale | Deepest layer | Single layer of basal cells | Constantly divides producing keratinocytes; contains melanocytes and Merkel cells |
Callus Formation
- Calluses form when stratum basale responds to frequent abrasion by producing more cells
- Extra cells mature and thicken the stratum corneum layer
- Commonly develops on feet or fingers experiencing repeated friction
Dermal Structure
- Dermis is connective tissue layer containing blood vessels unlike epidermis
- Contains sweat glands, hair follicles, and nerves
- Collagen fibers provide structural support while elastin fibers give elasticity
- Fibroblasts are specialized cells producing collagen and elastin proteins
- Papillary layer has loosely arranged connective tissue
- Reticular layer has densely packed connective tissue
Scar Formation
- Cuts limited to epidermis typically heal without scarring
- Cuts reaching dermis often produce scars due to altered collagen arrangement
- Fibroblasts produce collagen in different pattern than original skin structure
- Accessory structures like sweat glands and hair follicles don't regenerate in scars
- Scar tissue has reduced elasticity potentially affecting movement for large scars
- Keloids form from excessive collagen production continuing after wound heals
Hypodermis
- Located beneath dermis connecting skin to bone and muscle tissue
- Contains adipose tissue (stored body fat) providing insulation
- Serves as attachment layer for integumentary system
Accessory Structures
- Sweat glands produce perspiration for body cooling via evaporation
- Blood vessels dilate (widen) allowing heat escape when hot
- Blood vessels constrict when cold conserving heat at body core
- Sebaceous glands produce oil keeping skin and hair waterproof
- Sebaceous glands lubricate dead keratinocytes on skin surface
Hair Structure
- Hair follicles located in dermis layer
- Hair bulb contains rapidly dividing cells via mitosis
- New cells push outward forming hair root as structure grows
- Hair shaft consists of keratin and is non-living tissue
Nail Structure
- Nail base originates from epidermis layer
- Nail body (visible portion) made of dead keratinocytes protecting finger/toe tips
- Nail root contains frequently dividing cells pushing outward for nail growth
Skin Cancer Types
- Skin cancer is most common cancer type in United States
- Basal cell carcinoma arises from basal cells (most common skin cancer)
- Melanoma develops from melanocytes and can be serious
- Merkel cell carcinoma originates from Merkel cells (aggressive and rare)
- Understanding integumentary system enables better skin cancer treatment approaches
Burn Classification
- Burn severity categorized by affected tissue layers (classification systems vary)
- First degree burns affect only epidermis layer
- Second degree burns damage epidermis and partial dermis
- Third degree burns destroy epidermis and entire dermis
- Fourth degree burns extend beyond skin damaging bones and muscles
- Third and fourth degree burns often less painful due to nerve damage
- Severe burns compromise fluid maintenance and infection protection requiring specialized treatment
Clinical Significance
- Medical personnel need extensive integumentary system knowledge for burn treatment planning
- Significant burns increase infection risk requiring immediate medical intervention
- Restoring integumentary system function essential for survival after major burns