Chapter 6 - Skeletal System Notes

Chapter 6 - Skeletal System

Objectives

  • Know the functions of the skeletal system.

  • Know how bones are classified.

  • Know the structure of bone.

  • Know the process of bone formation and development.

  • Know how bone repairs itself after a fracture.

  • Describe the effects of sunlight, nutrition, hormonal secretions, and exercise on bone development.

  • Understand the process of calcium homeostasis.

  • Describe the life-span changes in the skeletal system.

Word Bits

  • OSTEO- bone

  • -CYTE – cell

  • -BLAST – budding

  • -CLAST – broken

  • CHONDRO - cartilage

Origin

  • Skeletal System comes from the MESODERM Germ Layer.

Connective Tissue

  • Tendons – Dense Regular CT

  • Ligaments – Dense Regular CT

  • Cartilage – Hyaline Cartilage CT

  • Bone – Compact & Spongy Bone CT

Ligaments

  • Attach BONE to BONE.

Tendons

  • Attach MUSCLE to BONE.

Cartilage

  • Flexible connective tissue, weaker than bone but stronger than muscle.

  • Found in joints, rib cage, ear, nose, elbow, knee, ankle, bronchial tubes, intervertebral discs.

Types of Arthritis

  • Osteoarthritis: Mechanical wear and tear of joints.

  • Rheumatoid arthritis: Autoimmune disease, inflamed synovial membrane.

Cartilage Types

  • Hyaline

  • Fibrocartilage

  • Elastic

Perichondrium

  • Double-layered connective tissue sheath covering most cartilage.

Chondroblasts

  • Produce cartilage matrix, located in the perichondrium.

  • Secrete extracellular matrix, mature into chondrocytes.

Chondrocytes

  • Maintain the cartilage matrix, reside in a space called a lacuna.

Lacuna

  • Matrix enclosed compartments where chondrocytes sit.

Functions of the Skeletal System

  1. Supports body.

  2. Protects vital organs.

  3. Allows movement.

  4. Stores minerals.

  5. Aids red blood cell production.

  6. Stores chemical energy.

Skeletal System Functions

  • Support: Bones support the weight of the body and various organs.

  • Protection: Bones protect the brain, lungs, heart, and spinal cord.

  • Movement: Skeletal muscles use bones as levers to move the body.

  • Reservoir: Stores calcium, phosphorus, and adipose tissue.

  • Hematopoiesis: Blood cell formation in the red marrow of certain bones.

Classification of Bones

  • Long bones (e.g., humerus).

  • Flat bones (e.g., sternum).

  • Short bones (e.g., trapezoid).

  • Irregular bones (e.g., vertebra).

  • Sesamoid bones (e.g., patella).

Skeletal System Divisions

  • Axial Skeleton

  • Appendicular Skeleton

Categories of Bone Shape

  • Long Bones

  • Short Bones

  • Flat Bones

  • Irregular Bones

  • Sesamoid Bones

Long Bones

  • Longer than they are wide (e.g., humerus, femur).

Short Bones

  • Cube-like shape (e.g., carpals, tarsals).

Flat Bones

  • Thin and curved (e.g., cranial bones, scapula, sternum, ribs).

Irregular Bones

  • Complex shapes (e.g., facial bones, sphenoid, ethmoid, mandible).

Sesamoid Bones

  • Small, round bones in tendons (e.g., patella).

Bone Structure

  • Diaphysis: Shaft.

  • Medullary Cavity: Contains yellow & red marrow.

  • Endosteum: Membrane lining the medullary cavity.

  • Periosteum: Fibrous membrane covering the outer surface.

  • Epiphysis: Wider section at ends of bone.

  • Articular cartilage: Reduces friction & acts as a shock absorber.

  • Epiphyseal plate (line): Growth plate.

  • Spongy Bone: Light, porous bone filled with marrow.

  • Nutrient foramen: Opening for blood vessel entrance.

  • Nutrient artery: Artery that supplies medullary cavity with nutrients

Gross Anatomy of Flat Bones

  • Layer of spongy bone (dipole) lined on either side by a layer of compact bone.

Bone Composition

  • Cells

  • Extracellular Matrix: Collagen fibers and minerals.

Cells in Bone Tissue

  • Mesenchymal Stem Cell: Develops into other types of cells.

  • Osteoblast: Forms bone matrix.

  • Osteocyte: Maintains bone tissue.

  • Osteoclast: Resorbs bone.

Bone Matrix

  • Collagen Fibers: Provide flexibility.

  • Minerals: Provide hardness & strength (calcium phosphate & calcium carbonate = hydroxyapatite).

Compact (cortical) Bone

  • Denser and stronger.

  • Structures: Osteon (Haversian System), Lamellae, Canaliculi, Lacuna, Central Canal, Perforating Canal

Spongy (trabecular) Bone

  • Supports shifts in weight distribution.

  • Structures: Trabeculae, Osteocytes in lacunae.

Ossification

  • Osteogenesis

  • Bone Development

  • Bone Formation: Occurs via intramembranous ossification (direct conversion of mesenchymal tissue to bone, e.g., skull) or endochondral ossification (mesenchymal tissue to cartilage, then replaced by bone, e.g., long bones).

  • Bone Growth:

    • Length: At the epiphyseal plate.

    • Width: Appositional growth.

  • Epiphyseal Plate Zones: Reserve, Proliferative, Maturation & Hypertrophy, Calcified Matrix.

  • Appositional Growth: Osteoclasts resorb old bone in the medullary cavity, while osteoblasts create new bone beneath the periosteum.

  • Fracture Repair Events:

    1. Blood clots (hematoma forms).

    2. Bone cells die.

    3. Chondrocytes create an internal callus.

    4. Periosteal cells create an external callus.

    5. Osteoclasts resorb dead bone; osteogenic cells activate.

    6. Cartilage is replaced by trabecular bone.

    7. Calluses unite; compact bone replaces spongy bone.

  • Factors Affecting Development: Sunlight (Vitamin D), nutrition (calcium), hormones (growth hormone), exercise (mechanical stress).

  • Hormones: Growth Hormone (bone growth), Thyroxine (bone matrix), Estrogen/Testosterone (osteoblast activity), Calcitriol (increases calcium).

  • Calcium Homeostasis: Bones store calcium; calcium is deposited/released based on blood levels. Low calcium = PTH, High calcium = Calcitonin.

  • Life-Span Changes: Bone mass decreases (age 30+), cartilage thins, joints stiffen.