Chapter 6 LV15.2

Chapter 6 Learning Objectives

  • Describe six major functions of the skeletal system:

    • Support

    • Protection of internal organs (e.g., brain, heart)

    • Assistance in movement (collaboration with muscles)

    • Mineral homeostasis (storage/release of calcium and phosphorus)

    • Blood cell production (hemopoiesis)

    • Storage of triglycerides in yellow marrow adipose cells

  • Structure and functions of long bone parts:

    • Compact vs. spongy bone properties

    • Classification of bone tissue as connective tissue

    • Cellular composition of bone tissue and cell functions

    • Blood and nerve supply of bones

    • Processes and purposes of bone growth and remodeling

    • Steps of intramembranous and endochondral ossification

    • Growth in length and thickness of bones

    • Bone remodeling processes

    • Common types of fractures and their repair sequences

    • Calcium's regulatory importance in the body

    • Influence of exercise and mechanical stress on bone tissue

    • Age-related effects on bone tissue

    • Disorders affecting bone tissue

Functions of Bone and the Skeletal System

  • Skeletal System Framework: An organ made of various tissues that includes:

    • Bone

    • Cartilage

    • Dense connective tissue

    • Adipose tissue

    • Nervous tissue

Functions of the Skeletal System

  1. Provides support

  2. Protects internal organs (brain, heart, etc.)

  3. Assists in body movements (with muscles)

  4. Mineral homeostasis (stores/releases calcium, phosphorus)

  5. Participates in blood cell production (hemopoiesis)

  6. Stores triglycerides in adipose cells of yellow marrow

Structure of Bone

  • A long bone consists of several key components:

    • Diaphysis: Shaft of the bone

    • Epiphyses: Ends at the joints

    • Metaphyses: Regions between diaphysis and epiphyses

    • Articular Cartilage: Covers both epiphyses

    • Periosteum: Connective tissue surrounding the diaphysis

    • Medullary Cavity: Hollow space in diaphysis

    • Endosteum: Membrane lining the medullary cavity

Basic Structure of Long Bones

  • Diaphysis: Shaft or main part

  • Epiphysis: Ends of the bone

  • Metaphysis: Region where diaphysis meets epiphysis, includes the epiphyseal plate in growing bones

  • Articular Cartilage: Covers epiphysis to facilitate joint movement

  • Periosteum and Medullary Cavity: Protection and support layers

Histology of Bone

  • Bone has a rich extracellular matrix comprised of:

    • 15% water

    • 30% collagen

    • 55% crystalline mineral salts

Cell Types in Bone Tissue

  1. Osteoprogenitor Cells: Bone stem cells that can differentiate into osteoblasts

  2. Osteoblasts: Bone-forming cells that secrete the matrix; do not divide

  3. Osteocytes: Mature bone cells that maintain tissue; do not secrete matrix

  4. Osteoclasts: Cells responsible for bone resorption; essential for repairing and remodeling bone

Compact Bone vs. Spongy Bone

  • Compact Bone

    • Provides protection and support

    • Contains osteons (Haversian systems)

    • Central canals run longitudinally with concentric lamellae around them

  • Spongy (Cancellous) Bone

    • Lighter structure with irregular lamellae arranged in trabeculae

    • Predominantly found in short, flat, and irregular bones as well as epiphyses of long bones

    • Involved in hemopoiesis in adults, mainly located in hips, ribs, sternum, vertebrae, skull,

Blood and Nerve Supply of Bone

  • Periosteal arteries penetrate the diaphysis through Volkmann's canals, accommodating periosteal veins

  • Nutrient arteries enter through nutrient foramen; nutrient veins exit the same canal

  • Epiphyses and metaphyses have their own arterial and venous supply

Bone Formation (Ossification)

  • Ossification is the process of bone development, beginning around the 6th week of embryonic life

  • Occurs through:

    • Intramembranous Ossification: Direct formation of bone within loose connective tissue

    • Endochondral Ossification: Replacement of hyaline cartilage with bone

Steps in Intramembranous Ossification

  1. Formation of ossification center

  2. Secretion of matrix to become osteocytes

  3. Development into trabeculae and formation of spongy bone

  4. Development of periosteum and conversion to compact bone

Steps in Endochondral Ossification

  1. Development of cartilage precursor

  2. Growth of cartilage model by chondrocyte division

  3. Establishment of the primary ossification center

  4. Secondary ossification center development

  5. Formation of articular cartilage and epiphyseal plates

Fracture and Repair of Bone

  1. Formation of Fracture Hematoma: Blood leak forms a clot at fracture site, causing inflammation

  2. Fibrocartilaginous Callus Formation: Tissue bridges fracture ends

  3. Bony Callus Formation: Osteoprogenitor cells develop into osteoblasts; hard callus forms

  4. Bone Remodeling: Resorption of old bone and replacement with new bone tissue

Common Types of Fractures

  • Open (Compound): Broken ends protrude through the skin

  • Comminuted: Bone splintered or crushed

  • Greenstick: Partial fracture, mostly seen in children

  • Impacted: One end driven into the other

  • Pott: Distal fibula especially

  • Colles: Distal radius, often near wrist joint

Bone's Role in Calcium Homeostasis

  • Bones store 99% of body's calcium, regulating levels via:

    • Parathyroid hormone (PTH) secretion during low calcium levels

    • Osteoclast stimulation to increase bone resorption and calcium release

Aging and Bone Tissue

  • Bone formation is greater than loss in youth; balances out in adults; older adults, especially post-menopausal women, lose bone mass

Summary of Factors Affecting Bone Growth

Minerals

  • Calcium, phosphorus, magnesium, fluoride, manganese are essential for strong bone matrix

Vitamins

  • Vitamins A, C, D, K, and B12 are crucial for bone health, influencing growth and repair

Hormones

  • Growth hormone, insulin-like growth factors (IGFs), sex hormones stimulate bone formation and remodeling

  • Parathyroid hormone (PTH) and calcitonin regulate calcium levels in bones

Bone Disorders

  • Osteoporosis: Weakened bones due to imbalance in resorption and formation

  • Paget's Disease: Abnormal remodeling causing thickened bone segments

  • Osteomyelitis: Inflammation of bone often due to infection