Skeletal Basics
List the AT LEAST 3 of the main functions of the skeletal system.
1. Support – Bearing the weight of the body.
2. Protection – Encases essential organs (e.g. the ribcage protects the heart and lungs).
3. Storage – Stores minerals (like calcium) and fat in yellow bone marrow.
4. Manufacturing – Produces red and white blood cells (hematopoiesis) in red bone marrow.
5. Movement – Joints provide movement; bones serve as attachment points for muscles.
Name the three main regions of a long bone.
Epiphyses – ends of bone. Metaphysis – between ends and shaft. Diaphysis – long central shaft.
Explain how bone marrow changes with age.
Red marrow (hematopoietic tissue) is gradually replaced by yellow marrow (fat tissue) as blood cell production becomes less necessary; yellow marrow serves as an energy reserve.
What are osteogenic cells and what do they form?
Undifferentiated stem cells with high mitotic activity that become osteoblasts and osteocytes (which no longer divide).
How does bone form on cartilage during growth?
Bone develops on a cartilage model; most fetal cartilage is replaced before birth. The cartilage matrix (hyaluronic acid, chondroitin sulfate, collagen, water) is calcified and replaced by bone.
What does “support” and “protection” mean as skeletal functions?
Bones encase vital organs (skull for brain, ribcage for heart/lungs) and form a rigid framework that supports the body and maintains shape.
What is the epiphyseal plate and what is its purpose?
A thin line of cartilage (growth plate) where new bone forms, allowing lengthwise growth.
Describe the structure and function of compact bone.
Located beneath periosteum, composed of osteons arranged in concentric lamellae around a central (Haversian) canal; Volkmann’s canals connect central canals. Provides rigidity and support.
What do osteoblasts do, and where are they found?
Found in growing portions of bone; they form new bone by secreting collagen and calcium salts.
What are the stages of bone repair?
1. Hematoma forms – blood enters wound, cells die, phagocytes clean debris. 2. Callus forms – vessels grow, cartilage bridges bone ends. 3. Callus ossifies – spongy bone replaces cartilage. 4. Compact bone forms – osteoclasts enlarge medullary cavity, spongy becomes compact.
What is hematopoiesis, and where does it occur?
The production of red and white blood cells in the red bone marrow of certain bones such as the sternum, pelvis, and ends of long bones.
What is the function of articular cartilage?
Covers bone ends, provides smooth movement at joints, and acts as a shock absorber.
Describe the structure and function of spongy bone.
Found at ends of long bones and under compact bone; has a lattice of trabeculae that form lines of stress for resistance to compression and shock absorption; spaces between trabeculae contain red marrow and blood vessels.
Describe osteocytes and their function.
Mature bone cells in lacunae; connected by cytoplasmic extensions through canaliculi, which connect bone cells and allow nutrient/waste exchange.
What is the difference between closed and open reduction in fracture repair?
Closed reduction: non-surgical bone alignment. Open reduction: surgical exposure and alignment of the fracture.
Define articulations, projections, and holes in bone.
Articulations: where two bones meet. Projections: raised areas for tendon/ligament attachment. Holes: openings for blood vessels and nerves.
Describe the medullary cavity and what lines it.
Hollow central region of the diaphysis, lined with endosteum, and filled with bone marrow (red in young, yellow in adults). Site of hematopoiesis.
What are the two main chemical components of bone and what do they do?
35% osteoid (organic): ground substance and collagen for flexibility and tensile strength. 65% mineral salts (inorganic): crystalline hydroxyapatites for hardness and strength.
What do osteoclasts do and what are they derived from?
Break down bone (resorption) to release calcium; develop from monocytes and macrophages.
What complications can result from fractures?
Fat embolism syndrome (fat from marrow enters blood and travels to lungs, causing breathing difficulty/confusion) and blood clots.
Name and describe the five types of bones by shape and give an example of each.
Long – longer than wide (femur). Short – cube-like (carpals). Flat – thin and broad (sternum). Irregular – complex shape (vertebrae). Sesamoid – small and round, embedded in tendons (patella).
What is the periosteum and what are its functions?
A connective tissue membrane covering the outer surface of bone; contains blood vessels, nerves, and lymphatic vessels; serves as a site for muscle attachment and bone repair.
Compare the functions of the periosteum, endosteum, and medullary cavity.
Periosteum: outer covering with vessels/nerves for attachment and repair. Endosteum: inner lining of medullary cavity for bone growth and remodeling. Medullary cavity: hollow region containing marrow and aiding in hematopoiesis or fat storage.
Explain how growth at the epiphyseal plate leads to bone elongation.
At the epiphyseal plate, chondrocytes divide and die as the matrix calcifies; they are replaced by osteoblasts, which form spongy bone; osteoclasts enlarge the medullary cavity to allow marrow space for cells.
How can bones heal improperly, and what determines proper realignment?
Bones can heal with or without anatomical realignment. If not reset correctly, the bone will heal in a deformed position, affecting function and strength.