Skeletal System
🦴 Skeletal System - LPN Notes
1. Overview of the Skeletal System
Parts: Bones, joints, cartilage, ligaments.
Functionality: Living, metabolically active tissue despite its appearance.
Number of bones: 206 in the adult human body.
Fun fact: A 70-year-old has likely replaced their entire skeleton 7 times in life.
2. Functions of the Skeletal System
Supports the body’s framework.
Protects internal organs.
Facilitates movement with muscles.
Stores minerals: Calcium and Phosphorus.
Produces blood cells in red marrow (hematopoiesis).
Regulates blood calcium levels.
3. Types of Bones
Type | Description | Examples |
|---|---|---|
Long Bones | Longer than wide | Femur, humerus, phalanges |
Short Bones | Cube-shaped | Carpals (wrist), tarsals (ankle) |
Flat Bones | Thin, flat, and curved | Skull, ribs, sternum, scapulae |
Irregular | Complex shapes | Vertebrae, pelvic bones, some skull bones |
4. Bone Tissue
Osseous Tissue: Bone tissue.
Osteoblasts: Build bone by secreting matrix.
Osteocytes: Mature bone cells maintaining bone.
Osteoclasts: Break down bone for remodeling & calcium release.
5. Types of Bone Tissue
Type | Features | Location |
|---|---|---|
Compact Bone | Dense, strong, forms outer bone & diaphysis | Shaft of long bones |
Spongy Bone | Light, porous, contains red marrow | Ends of long bones, flat/irregular bones |
Structural unit of compact bone: Haversian (osteon) system.
Spongy bone: Contains trabeculae; red marrow resides here.
6. Parts of a Long Bone
Part | Description |
|---|---|
Diaphysis | Shaft; compact bone for strength |
Epiphysis | End of the bone; spongy bone + articular cartilage |
Epiphyseal Disc | Growth plate; allows longitudinal growth |
Medullary Cavity | Hollow center; red marrow in infants, yellow marrow in adults |
Periosteum | Outer covering; contains blood vessels and nerves |
Articular Cartilage | Smooth cartilage on epiphysis to reduce joint friction |
7. Bone Formation - Ossification
Definition: Process of bone formation.
Begins in fetal development.
Types of Ossification:
Type | Description |
|---|---|
Intramembranous | Flat bones form from membranes |
Endochondral | Long bones form by replacing cartilage |
8. Bone Growth
Longitudinal Growth (Height):
Occurs at epiphyseal disc (growth plate).
Controlled by:
Growth Hormone (GH) → stimulates growth.
Estrogen/Testosterone → fuse plate, end growth.
📌 Injuries to growth plates in children can impair growth.
Appositional Growth (Width):
Osteoblasts add bone on outer surface.
Osteoclasts break down bone inside → widen medullary cavity.
Called bone remodeling.
Weight-bearing & exercise ➜ Stimulate bone growth
Sedentary lifestyle ➜ Bone loss (ex: osteoporosis)
9. Bone Surface Markings
Projections: Muscle/tendon/ligament attachment.
Depressions & grooves: Paths for nerves/blood vessels.
Examples:
Foramen: Hole for blood vessels/nerves
Fossa: Shallow depression
Tuberosity: Large rounded projection
10. Osteoporosis
Common in postmenopausal women due to low estrogen.
Causes:
↓ Bone-building activity
↑ Bone resorption
Risk factors:
Sedentary lifestyle
High phosphate (soda)
Steroids
Weight-loss pills (thyroid hormone)
📌 Common fracture sites: hips, wrists, vertebrae
Leads to shrinking, pain, organ impairment.
11. Bone Fractures
Type | Description |
|---|---|
Simple | Bone breaks cleanly, skin intact |
Compound | Bone breaks through skin |
Greenstick | Partial fracture (common in children) |
Spiral | Bone twisted apart |
Comminuted | Bone shatters into fragments |
Impacted | Bone ends jam together |
12. Clinical Pearls
Bone remodeling is lifelong.
Bone resorption moves calcium into bloodstream.
Parathyroid hormone (PTH) stimulates osteoclast activity.
Weight-bearing activities preserve bone mass.
✅ Quick Memory Tricks
"Osteo" = Bone
"Blast" = Build, "Clast" = Crush
Compact = Strong shell, Spongy = Light, red marrow
Growth Plate = Epiphyseal Disc
Ossification = Formation