• Chapter 6: Hyaline, Elastic, and Fibrocartilage Help Form the Skeleton

6.1: Structural Properties of the Three Types of Cartilage Tissue

Cartilage is a specialized connective tissue that provides support, flexibility, and resilience in various parts of the skeleton. The three main types of cartilage are hyaline cartilage, elastic cartilage, and fibrocartilage, each with distinct properties and functions.

• Elastic cartilage: Maintains the shape of a structure while allowing great flexibility. Example: External ear.

• Fibrocartilage: Resists compression and provides great tensile strength. Example: Intervertebral discs.

• Hyaline cartilage: Provides support with flexibility and resilience. Example: Articular surfaces of bones.

6.1b: Major Cartilages of the Adult Skeleton

Cartilage is distributed throughout the body, serving various structural and functional roles. The table below summarizes the location and type of major cartilages:

6.1c: Cartilage Growth

Cartilage grows by two mechanisms:

• Interstitial growth: New cartilage forms from within existing cartilage tissue.

• Appositional growth: New cartilage tissue is added at the periphery of existing cartilage tissue.

The extracellular matrix of cartilage is flexible, allowing for mitosis and growth.

Chapter 6.2: Bones Perform Several Important Functions

6.2: Functions of the Skeleton and Bone Tissue

Bones are dynamic organs that perform a variety of functions essential for movement, protection, and homeostasis. The table below summarizes these functions:

Chapter 6.3: Major Regions of the Skeleton and Bone Classification

6.3a: Major Regions of the Skeleton

The skeleton is divided into two main regions:

• Axial skeleton: Includes bones of the skull, vertebral column, and rib cage. Functions mainly in protection, support, and carrying other body parts.

• Appendicular skeleton: Consists of bones of the upper and lower limbs and the girdles that attach the limbs to the trunk. Functions mainly in movement and manipulation of the environment.

6.3b: Bone Classes and Examples

Bones are classified into four groups based on their shape:

• Long bones: Longer than they are wide; e.g., femur, humerus.

• Short bones: Cube-shaped; e.g., bones of the wrist and ankle.

• Flat bones: Thin, flattened, and usually curved; e.g., sternum, scapula.

• Irregular bones: Complicated shapes; e.g., vertebrae, hip bones.

Chapter 6.4: Bone Structure and Composition

6.4a: Gross Anatomy of Flat and Long Bones

Bones consist of outer compact bone and inner spongy bone. Key structures include:

• Endosteum: Membrane lining the internal bone surface.

• Articular cartilage: Covers joint surfaces.

• Spongy bone: Internal network of trabeculae.

• Compact bone: Dense outer layer.

• Yellow bone marrow: Fat storage tissue.

• Periosteum: Membrane covering the external bone surface.

• Diaphysis: Shaft of a long bone.

Red bone marrow is found in the trabeculae of spongy bone in flat bones (skull, sternum, ribs, clavicles, scapulae, hip bones, vertebrae) and in the heads of the femur and humerus.

6.4b: Functional Importance of Bone Markings

Bones have markings that serve as sites for muscle and ligament attachment, form joints, or act as depressions/openings for nerves and blood vessels.

6.4c: Histology of Compact and Spongy Bone

Bones are composed of compact and spongy tissue, each with unique structures:

• Osteons: Compact bone only

• Trabeculae: Spongy bone only

• Osteocytes: Both compact bone and spongy bone

• Canaliculi: Both compact bone and spongy bone

6.4d: Chemical Composition of Bone

Bones are composed of organic and inorganic components:

• Organic components: Cells and osteoid (ground substance and collagen fibers). Provide flexibility and tensile strength.

• Inorganic components: Mineral salts, mainly hydroxyapatite (calcium phosphates). Provide hardness and resistance to compression.

Analogy: Organic components are like reinforcing bars in concrete, providing flexibility and strength. Inorganic components are like the concrete itself, providing hardness and resistance to compression.

Chapter 6.5: Bone Development and Ossification

6.5a: Intramembranous vs. Endochondral Ossification

Bones develop by two processes:

• Intramembranous ossification: Bone develops from a fibrous membrane. Most flat bones form this way.

• Endochondral ossification: Bone develops by replacing hyaline cartilage. Most bones of the skeleton are formed by this process.

Key steps in endochondral ossification:

1. Cartilage calcifies in the center of the diaphysis and then develops cavities.

2. Periosteal bud invades the internal cavities and spongy bone forms.

3. Secondary ossification centers appear in the epiphyses; a medullary cavity forms in the diaphysis.

4. Epiphyses ossify.

5. A bone collar forms around the diaphysis of the hyaline cartilage model.

Most bones that form by intramembranous ossification are flat bones.

Key Terms and Concepts

• Osteon: Structural unit of compact bone.

• Trabeculae: Network of spongy bone.

• Osteocyte: Mature bone cell that maintains bone matrix.

• Osteoblast: Bone-forming cell.

• Osteoclast: Bone-resorbing cell.

• Canaliculi: Tiny canals connecting osteocytes.

• Lamellae: Layers of bone matrix in compact bone.

Formulas and Equations

• Bone strength:

• Ossification:

Additional info: These notes expand on the original content by providing definitions, examples, and academic context for each topic, ensuring a comprehensive and self-contained study guide for Anatomy & Physiology students.