DC

Articulations

Introduction

  • Reminder to keep track of upcoming content and PowerPoint presentation.

  • Lab announcement regarding skull study, including tutor availability and independent inquiry room hours (Tuesday and Thursday from 09:30 to 15:30).

  • Skull availability in library for studying.

Upcoming Assessments

  • Announcement of Quiz 2, covering material from the introductory chapter and skull bones.

Bone Growth

Types of Bone Growth

  • Longitudinal Growth

    • Step 1: Chondrocytes divide in the zone of proliferation (Chondro means cartilage).

    • Step 2: Chondrocytes enlarge and mature; lacunae surrounding chondrocytes become larger.

    • Step 3: Chondrocytes die, matrix calcifies; osteoblasts invade calcified cartilage to lay down bone.

    • Step 4: Osteoclasts absorb calcified cartilage, replaced by bone.

Concept Explanation

  • Growth starts as cartilage, enlarges, and then becomes calcified, forming bone.

  • Important to understand terminology, especially "osteoblasts" (cells that form bone) and "osteoclasts" (cells that break down bone).

Bone Growth in Width (Appositional Growth)

  • Osteoblasts lay down bone between periosteum and bone surface.

  • Formation of new lamellae; old lamellae are incorporated or removed to maintain inner structure.

  • Compact bone thickens primarily in the diaphysis (shaft of the bone).

  • Osteoclasts digest the inner cavity to lighten bone weight, preventing it from becoming overly dense.

Factors Affecting Bone Strength

  • Stress applied to bones increases their strength.

Hormonal Control of Bone Growth

  • Growth hormone (produced by anterior pituitary) stimulates bone growth.

    • Related to growth spurts during childhood and adolescence.

  • Thyroid hormones affect metabolism and tissue growth.

  • Estrogen and testosterone influence growth and epiphyseal plate closure.

    • Estrogen typically leads to closure by ages 14-15; testosterone by ages 16-17.

Bone Remodeling

Definition and Importance

  • Bone remodeling = continual process of bone formation (deposition) and loss (resorption).

  • Osteoclasts break down bone while osteoblasts build it up, fixing small cracks and maintaining health.

  • Physical stress applied during activities promotes stronger bone growth.

  • Astronauts face weakening of bones due to lack of gravity.

Nutritional Factors Affecting Bone Health

  • Calcium intake is essential for deposition; vitamin D necessary for calcium absorption; vitamin K extends osteoblast lifespan; vitamin C is important for collagen production.

  • High protein intake can alter blood pH, leading to resorption of calcium and phosphorus.

  • Main dietary sources: Dairy for calcium, colonic bacteria for vitamin K, daily intake of vitamin C.

Calcium Homeostasis

  • Calcium is vital for muscle contraction, nerve impulses, and blood clotting.

  • Calcium levels in the blood are controlled through negative feedback:

    • Parathyroid hormone (PTH): Increases blood calcium by stimulating osteoclast activity (bone breakdown).

    • Calcitonin: Decreases blood calcium by promoting storage in bones.

  • High PTH may lead to hypercalcemia, risking kidney issues and bone weakness.

Bone Repair Process

Steps in Bone Healing

  1. Hematoma Formation: Ruptured blood vessels fill the site, cutting off blood supply.

  2. Formation of Soft Callus: Fibroblasts and chondroblasts produce fibers and cartilage to infiltrate the hematoma.

  3. Hard Callus Formation: Osteoblasts create a bony callus over several weeks.

  4. Remodeling: Primary bone is replaced with secondary bone over several months for organized structure.

Types of Bone Fractures

  • Simple/Closed Fracture: Skin intact.

  • Compound/Open Fracture: Bone protrudes through the skin.

  • Noted treatment includes immobilization and potential surgical intervention for open fractures.

Articulations (Joints)

Joint Classification

Functional Classification

  • Synarthrosis: No movement (e.g., skull sutures).

  • Amphiarthrosis: Limited movement (e.g., wrist joints).

  • Diarthrosis: Free movement (e.g., shoulder joint, least stable).

Structural Classification

  • Fibrous Joints: Dense regular connective tissue links bones. No joint space.

  • Cartilaginous Joints: Cartilage between articulating bones. No joint space.

  • Synovial Joints: Joint cavity encapsulated by synovial fluid.

Types of Fibrous Joints

  • Sutures: Connect skull bones, stable.

  • Gomphoses: Joint between tooth and jawbone; stable.

  • Syndesmoses: Connected by interosseous membranes (e.g., between radius and ulna).

Types of Cartilaginous Joints

  • Synchondroses: Joined by hyaline cartilage (e.g., epiphyseal plate, sternocostal joint).

  • Symphyses: Joined by fibrocartilage, allowing slight movement (e.g., pubic symphysis, intervertebral discs).

Synovial Joint Characteristics

  • Articular Capsule: Dense irregular connective tissue outer layer and synovial membrane inner layer.

  • Synovial Fluid: Lubricates joints, distributes stress, nourishes cartilage.

  • Articular Cartilage: Covers bone ends; primarily hyaline cartilage.

  • Other structures may include ligaments, tendons, bursa, and menisci for added stability and cushioning.

Conclusion

  • Understand the structure and function of joints to aid in identifying issues related to movement, stability, and potential injuries.

  • Importance of maintaining joint health using proper nutrition and physical activity.