STUDYGUIDE-CH6

6.1 Hyaline, Elastic, and Fibrocartilage

Learning Outcomes:
- Describe the functional properties of the three types of cartilage.
- Locate major cartilages in the adult skeleton.
- Explain cartilage growth.
Basic Structure:
1. Skeletal cartilages are composed of cartilage, encased in perichondrium (dense irregular connective tissue).
2. Hyaline Cartilage: Most common; found in articular, costal, respiratory, and nasal regions.
3. Elastic Cartilage: More flexible; found in external ear and epiglottis.
4. Fibrocartilage: Found in high-pressure areas (e.g., knee, intervertebral discs).
Growth of Cartilage:
1. Appositional Growth: Outward expansion by adding cartilage matrix at the surface.
2. Interstitial Growth: Expansion from within due to division of chondrocytes and matrix secretion.

Learning Outcome: Describe the functions of the skeleton and bone tissue.
Functions of Bones:
1. Support: Provides framework and surrounds organs.
2. Protection: Shields brain and vital organs.
3. Anchorage: Skeletal muscles attach via tendons.
4. Mineral Storage: Stores calcium and phosphate.
5. Blood Cell Formation: Hematopoiesis in red bone marrow.
6. Triglyceride Storage: Fat found in yellow bone marrow.
7. Hormone Production: Produces osteocalcin for insulin regulation.

Learning Outcomes: Name major regions and classify bones by shape.
Skeletal Divisions:
1. Axial Skeleton: Skull, vertebral column, rib cage; supports and protects.
2. Appendicular Skeleton: Limb bones and girdles; aids in movement.
Bone Classes by Shape:
1. Long Bones: Longer than wide; includes all limb bones (except patella and wrist/ankle bones).
2. Short Bones: Cube-shaped; includes carpals, tarsals, patella.
3. Flat Bones: Thin, curved; includes skull bones, sternum, scapulae, ribs.
4. Irregular Bones: Complex shapes (e.g., vertebrae, hip bones).

Learning Outcomes: Describe anatomy of flat and long bones; identify marrow locations, and explain bone markings.
Gross Anatomy:
1. Compact and Spongy Bone:
  - Compact bone: Dense outer layer.
  - Spongy bone: Contains trabeculae (needle-like structures).
2. Structure of Bones:
  - Short/Flat Bones: Thin plates of compact bone around spongy bone (diploë).
  - Long Bones: Tubular diaphysis with medullary cavity; epiphyses contain spongy bone with articular cartilage.
3. Blood and Nerve Supply: Blood vessels and nerves enter through nutrient foramina; similar supply in epiphyses.
4. Hematopoietic Tissue: Red marrow located in trabecular cavities and diploë.
  - In infants, red marrow fills entire medullary cavities; in adults, it's primarily in proximal epiphyses.
5. Bone Markings:
  - Projections for attachment, joint surfaces, depressions/openings for vessels/nerves.
Microscopic Anatomy:
1. Bone Cells: Osteoprogenitor cells, osteoblasts, osteocytes, bone lining cells, osteoclasts.
  - Structural unit: Osteon (Haversian system), with central canals and lamellae.
2. Canals: Volkmann’s canals connect blood supplies; lacunae contain osteocytes.
3. Lamellae: Circumferential lamellae (outer) & interstitial lamellae (between osteons).

Organic Composition: Cells and osteoid (collagen, ground substance); provides flexibility.
Inorganic Composition: 65% of bone mass; hydroxyapatites (calcium phosphates); confers hardness and resistance to compression.

Learning Outcomes: Compare intramembranous vs endochondral ossification; describe epiphyseal plates in bone growth.
Formation of the Bony Skeleton:
1. Endochondral Ossification: Hyaline cartilage replaced by bone for all bones below the skull (except clavicles).
  - Osteoblasts form bone collar around diaphysis.
  - Cartilage calcifies, forming cavities; periosteal bud forms spongy bone.
2. Intramembranous Ossification: Bone forms from fibrous connective tissue membranes (cranial bones and clavicles).
  - Mesenchymal cells differentiate into osteoblasts.
  - Osteoid is secreted, leading to formation of immature spongy bone and periosteum.