Anatomy and Physiology: Skeletal System

Anatomy and Physiology 50A - Chapter 6 Lecture Notes

Cartilage in the Skeletal System

• Skeletal Cartilage: Composed of a gel-like matrix and three main types:
  • Hyaline Cartilage: Provides support while being flexible, found in joint surfaces, rib cartilage, and respiratory structures.
  • Elastic Cartilage: Similar to hyaline, but with more elastic fibers, found in the ear and epiglottis.
  • Fibrocartilage: Has dense collagen fibers for tensile strength, found in intervertebral discs and pubic symphysis.
• Growth of Cartilage: Occurs through appositional (growth from outside) and interstitial (growth from within) methods.

Functions of Bone

• Support: Provides a framework for the body and cradles soft organs.
• Protection: Encases vital organs, e.g., the skull protects the brain.
• Anchorage: Serves as attachment points for muscles, facilitating movement.
• Mineral and Growth Factor Storage: Stores calcium and phosphorus, important for maintaining bone health and metabolic functions.
• Blood Cell Production: Houses red bone marrow, which produces blood cells (hematopoiesis).
• Fat Storage: Yellow bone marrow serves as an energy reserve.
• Hormone Production: Bones produce hormones (e.g., osteocalcin) that influence blood sugar regulation and fat deposition.

Bone Classification

• Axial Skeleton: Comprises the skull, vertebral column, and rib cage.
• Appendicular Skeleton: Comprises limbs and girdles (shoulder and pelvis).
• Long Bones: Longer than they are wide, e.g., femur; characterized by a diaphysis (shaft) and epiphyses (ends).
• Short Bones: Cube-shaped, e.g., carpals and tarsals.
• Sesamoid Bones: Small bones embedded in tendons, function in protecting tendons from stress, e.g., patella.
• Flat Bones: Thin, flattened bones, e.g., sternum, cranial bones; primarily for protection and muscle attachment.
• Irregular Bones: Complex shapes, e.g., vertebrae; serve various functions.

Gross Anatomy of Bones

• Compact Bone vs. Spongy Bone:
  • Compact Bone: Dense outer layer, provides strength and support.
  • Spongy Bone: Internal structure, lighter, with trabeculae providing support and housing red marrow.
• Structure of Short, Irregular, and Flat Bones:
  • Composed of thin plates of periosteum-covered compact bone surrounding spongy bone.
• Structure of Long Bone:
  • Diaphysis: Shaft, hollow center (medullary cavity) containing yellow marrow.
  • Epiphysis: Ends, with articular cartilage covering joint surfaces.
• Membranes:
  • Periosteum: Dense connective tissue covering the bone, important for growth and repair.
  • Nutrient Foramina: Openings allowing blood vessels to enter bones.
• Hematopoietic Tissue: Found in red marrow, responsible for blood cell production.
• Bone Markings: Surface features (e.g., projections, depressions) allowing attachment of muscles, tendons, and ligaments.

Microscopic Anatomy of Bones

• Cells in Bones:
  • Osteogenic Cells: Stem cells that differentiate into osteoblasts.
  • Osteoblasts: Bone-forming cells that secrete the bone matrix.
  • Osteocytes: Mature bone cells maintaining bone tissue; reside in lacunae.
  • Bone Lining Cells: Flattened cells on bone surfaces, involved in bone maintenance.
  • Osteoclasts: Multinucleated cells responsible for bone resorption; originate from monocytes.
• Compact Bone Microscopic Structure:
  • Haversian System (Osteon): Structural unit of compact bone, containing a central canal, lamellae, and lacunae.
  • Lamellae: Rings of bone matrix; orientation affects bone strength.
  • Central Canal: Contains blood vessels and nerves; site of nutrient exchange.
  • Volkmann’s Canal: Connects central canals; carries blood vessels perpendicular to Haversian canals.
  • Lacunae: Small cavities housing osteocytes.
  • Canaliculi: Tiny canals connecting lacunae, facilitating communication between osteocytes.
  • Interstitial and Circumferential Lamellae: Help in bone structure and stability.