Integumentary and Skeletal System Study Notes
Posted on Mar 18, 2026 in Environmental Biology
1. Layers of the Skin
Epidermis (Outer Layer – Stratified Squamous Epithelium)
| Layer | Structure | Function |
|---|
| Stratum Basale | Single layer of stem cells, melanocytes | Cell division, skin regeneration, melanin production |
| Stratum Spinosum | Several layers of keratinocytes | Keratin production, immune defense (Langerhans cells) |
| Stratum Granulosum | Flattened keratinocytes with granules | Waterproofing, cells begin to die |
| Stratum Lucidum | Thin layer of dead cells (thick skin only) | Extra protection (palms & soles) |
| Stratum Corneum | 20–30 layers dead keratinized cells | Tough waterproof barrier against damage & pathogens |
Key Concepts
- Epidermis is avascular: No direct blood supply.
- Nutrients diffuse from the dermis.
Dermis (Connective Tissue Layer)
| Layer | Structure | Function |
|---|
| Papillary Layer | Areolar CT, dermal papillae, blood vessels | Nourishes epidermis, sensory receptors |
| Reticular Layer | Dense irregular CT, collagen fibers | Strength, elasticity, houses glands & hair follicles |
Key Concepts
- Dermis provides nutrients and structural support.
- Epidermis provides protection.
2. Accessory Structures of Skin
Hair
| Part | Function |
|---|
| Hair follicle | Anchors hair in dermis |
| Hair bulb | Growth region |
| Hair shaft | Visible hair above skin |
| Hair root | Hair within follicle |
| Arrector pili muscle | Causes goosebumps |
Nails
| Structure | Function |
|---|
| Nail plate | Hard visible nail |
| Nail bed | Skin under nail |
| Nail matrix | Produces new nail cells |
| Lunula | Crescent white area |
| Cuticle | Protects nail root |
| Hyponychium | Skin under free edge |
Glands
Sebaceous Glands
| Feature | Function |
|---|
| Holocrine glands | Release entire cell |
| Secrete sebum | Lubricates hair & skin |
| Antibacterial | Prevents drying |
Sweat (Sudoriferous) Glands
| Type | Structure | Function |
|---|
| Eccrine | Coiled tubular gland | Cooling via sweat evaporation |
| Apocrine | Open into hair follicles | Scent/pheromone secretion |
- Mammary glands: Produce milk.
- Ceruminous glands: Produce earwax.
3. Wound Healing
| Stage | What Happens | Purpose |
|---|
| Hemostasis | Blood clot forms | Stops bleeding |
| Inflammation | WBC clean debris | Prevent infection |
| Proliferation | Keratinocytes grow, angiogenesis | New tissue formation |
| Remodeling | Collagen reorganizes | Strengthens tissue |
4. Burns
| Degree | Depth | Symptoms | Healing |
|---|
| 1st Degree | Epidermis only | Red, painful | Heals quickly |
| 2nd Degree | Epidermis + dermis | Blisters, severe pain | May scar |
| 3rd Degree | Full thickness | White/charred, little pain | Requires skin graft |
Rule of Nines (Burn Surface Estimation)
- Head & Neck: 9%
- Each Arm: 9%
- Anterior Trunk: 18%
- Posterior Trunk: 18%
- Each Leg: 18%
- Perineum: 1%
5. Skeletal System
Axial vs. Appendicular Skeleton
- Axial: Skull, vertebral column, ribs, sternum.
- Appendicular: Limbs, shoulder girdle, pelvic girdle.
6. Cartilage
| Type | Location | Function |
|---|
| Hyaline | Joints, ribs, trachea | Smooth support |
| Elastic | Ear, epiglottis | Flexible support |
| Fibrocartilage | Intervertebral discs, meniscus | Shock absorption |
7. Bone Tissue
- Compact Bone: Dense, organized into osteons for strength.
- Spongy Bone: Network of trabeculae; contains bone marrow.
8. Bone Cells
| Cell | Function |
|---|
| Osteogenic cells | Stem cells → osteoblasts |
| Osteoblasts | Build bone matrix |
| Osteocytes | Maintain bone tissue |
| Osteoclasts | Break down bone (resorption) |
9. Bone Formation (Ossification)
- Intramembranous: Bone develops from mesenchyme (flat bones).
- Endochondral: Bone forms from hyaline cartilage (long bones).
10. Bone Hormone Regulation
| Hormone | Function |
|---|
| PTH | Raises blood calcium |
| Calcitonin | Lowers blood calcium |
| Calcitriol | Increases calcium absorption |
| Growth Hormone | Stimulates bone growth |
11. Joints (Articulations)
- Fibrous: Dense connective tissue (immovable).
- Cartilaginous: Joined by cartilage (slight movement).
- Synovial: Fluid-filled cavity (freely movable).
