Skeletal System: Bone Structure and Function

Chapter 7: Skeletal System: Bone Structure and Function

A. General Functions of Bone & the Skeletal System (PHYSIOLOGY)

• The skeletal system serves several critical functions, which can be categorized as follows:

  1. Support: Provides a rigid framework that supports the body and cradles soft organs.

  2. Movement: Works in conjunction with muscles to facilitate movement; bones act as levers.

  3. Protection: Safeguards vital organs (e.g., skull protects the brain, rib cage protects the heart).

  4. Mineral Storage: Stores minerals, particularly calcium and phosphorus, which are essential for numerous physiological processes.

  5. Blood Cell Production: Houses bone marrow, which produces blood cells (hematopoiesis).

B. Structural Components – Microscopic Anatomy (ANATOMY)

• The microscopic structure of bone consists of cellular and extracellular components:

  1. Cellular Components:

  • Osteogenic Cells: Precursor cells that differentiate into osteoblasts.

  • Osteoblasts: Cells responsible for bone formation by synthesizing bone matrix.

  • Osteocytes: Mature bone cells that maintain bone tissue.

  • Osteoclasts: Cells involved in bone resorption, breaking down bone tissue.

  1. Extracellular Components:

  • Bone Matrix: Composed of collagen fibers (providing tensile strength) and hydroxyapatite crystals (providing compressive strength).

• Internal Structural Components of Compact and Spongy Bone:

  3. Compact Bone:

  • Densely packed, forms the outer layer of bones, contains Haversian systems (osteons) for nutrient supply.

  3. Spongy Bone:

  • Lattice-like structure found mostly at the ends of long bones and in the interiors of others, contains red bone marrow.

• Types of Cartilage Tissues in the Skeletal System:

  5. Hyaline Cartilage: Found at joint surfaces, providing smooth surfaces for movement.

  6. Elastic Cartilage: Found in structures requiring flexibility (e.g., ear).

  7. Fibrocartilage: Provides support and can withstand pressure (e.g., intervertebral discs).

• Roles of Connective Tissues:

  8. Dense Regular Connective Tissue:

  • Found in ligaments and tendons; provides tensile strength.

  8. Dense Irregular Connective Tissue:

  • Provides strength in multiple directions, as seen in the joint capsules and periosteum.

C. Structural Components – Gross Anatomy (ANATOMY)

• Long Bone Structure:

  1. Diaphysis: The long shaft of the bone, primarily composed of compact bone.

  2. Epiphyseal Regions: The ends of long bones, containing spongy bone and covered by articular cartilage.

  3. Growth Plate (Epiphyseal Plate): Zone of cartilage where longitudinal growth occurs during development.

  4. Periosteum: A dense layer of connective tissue surrounding the bone, serving as a site for muscle attachment and containing blood vessels.

• Functions of Structural Components:

  5. The structure of long bones allows for:

  • Leverage for Movement: Bone shape facilitates muscle attachment.

  • Blood Cell Production: Red bone marrow located within spongy bone.

D. Physiology of Embryonic Bone Formation (Ossification, Osteogenesis) (PHYSIOLOGY)

• Roles of Osteogenic Cells in Bone Formation:

  1. Differentiate into osteoblasts, which then produce bone matrix.

• Comparison of Bone Formation Types:

  2. Intramembranous Ossification: Bone develops directly from mesenchyme (e.g., skull bones).

  3. Endochondral Ossification: Bone develops from a hyaline cartilage template (e.g., long bones).

E. Physiology of Bone Growth, Repair, & Remodeling (PHYSIOLOGY)

• Functional Comparison of Osteoblasts and Osteoclasts:

  1. Osteoblasts: Build bone by laying down new bone matrix.

  2. Osteoclasts: Resorb bone by breaking down the organic and inorganic bone components.

• Hormonal Regulation of Skeletal Growth:

  3. Hormones such as growth hormone, sex hormones, and thyroid hormones influence bone density and growth.

• Roles of Parathyroid Hormone and Calcitriol:

  4. Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating osteoclasts.

  5. Calcitriol (active form of Vitamin D): Enhances intestinal absorption of calcium, vital for bone health and remodeling.

F. Predictions Related to Homeostatic Imbalance, Including Disease States & Disorders (PHYSIOLOGY)

• Factors Affecting Skeletal System Homeostasis:

  1. Conditions that can lead to osteoporosis include age, hormonal changes, and nutritional deficiencies.

• Problems Arising from Osteoporosis:

  2. Increased risk of fractures, decreased bone density, and compromised structural integrity of bones leading to pain and disability.