Anatomy and Histology - Bone Tissue and Skeletal System

Chapter Objectives

  • List and describe the functions of bones.

  • Describe the classes of bones.

  • Discuss the process of bone formation and development.

  • Explain how bone repairs itself after a fracture.

  • Discuss the effect of exercise, nutrition, and hormones on bone tissue.

6.1 The Functions of the Skeletal System

  • Skeletal system: Composed of bones and cartilage, performing essential functions:

    • Support: Provides structural support for the body.

    • Facilitate movement: Works with muscles to enable mobility.

    • Protects internal organs: Shields vital organs such as the heart, lungs, and brain.

    • Produces blood cells (Hematopoiesis): Occurs in red bone marrow.

    • Stores and releases minerals and fat: Minerals like calcium and phosphorus are stored in bones; yellow bone marrow holds fat.

  • Bone: A dense connective tissue forming the skeleton.

  • Cartilage: A flexible connective tissue enhancing movement and adapting forces.

6.2 Bone Classification

  • The adult skeleton consists of 206 bones, classified into 5 categories based on shape:

    • Long Bones: Femur, Patella.

    • Short Bones: Carpals, Tarsals.

    • Flat Bones: Sternum, Scapula.

    • Irregular Bones: Vertebrae.

    • Sesamoid Bones: Developed within tendons; e.g., Patella.

6.3 Bone Structure

  • Gross Anatomy of Bone:

    • Diaphysis: The shaft or central part of a long bone.

    • Epiphysis: The ends of the bone, typically covered by articular cartilage.

    • Bone Marrow:

    • Red marrow: Site of blood cell production (hematopoiesis).

    • Yellow marrow: Fat storage tissue.

    • Bone Tissue Types:

    • Compact Bone: Dense, withstands compressive forces.

    • Spongy Bone: Lighter, supports shifts in weight distribution.

    • Bone Layers:

    • Periosteum: Fibrous membrane covering bone surfaces.

    • Endosteum: Lining of the medullary cavity containing bone-forming cells.

6.4 Bone Formation and Development

  • Ossification (osteogenesis): The process of bone development.

    • Two pathways:

    1. Intramembranous ossification: Forms bone directly from connective tissue.

    2. Endochondral ossification: Replacing hyaline cartilage with bone.

    • Two growth processes:

    1. Epiphyseal plate: Cartilage becomes bone, allowing length growth.

    2. Modeling: Increases bone diameter.

6.5 Fractures: Bone Repair

  • Types of Fractures:

    • Closed (Simple): Skin remains intact.

    • Open (Compound): Skin is pierced by the broken bone.

    • Transverse: Across the long axis of the bone.

    • Oblique: Diagonal line across the bone.

    • Spiral: Twisting fracture.

    • Comminuted: Bone is shattered into multiple pieces.

    • Impacted: One bone fragment is driven into another.

    • Greenstick: Partial fracture, typically in children.

  • Bone Repair Stages:

    1. Fracture Hematoma: Blood clot forms at the fracture site.

    2. Callus Formation: Internal and external calli form.

    3. Cartilage Replacement: Cartilage of the calli transforms into spongy bone.

    4. Remodeling: Compact bone replaces spongy bone for strength.

6.6 Exercise, Nutrition, Hormones, and Bone Tissue

  • Exercise:

    • Mechanical stress enhances bone deposition of minerals and collagen fibers.

  • Nutrition:

    • Essential minerals (calcium, phosphorus) and vitamins (D) are crucial for bone health.

  • Hormones:

    • Bone density peaks around 30 years of age; women experience rapid bone loss post-menopause, leading to osteoporosis.