Introduction to the Skeletal System

• The skeletal system consists primarily of osseous tissue (bone tissue).

• Osseous tissue is classified as a connective tissue.

Components of the Skeletal System

Ligaments

• Function: Connect bone to bone.

• Example: Anterior cruciate ligament (ACL) connects the tibia to the femur.

Cartilage

• Importance: Provides a friction-reducing surface at joints.

• Types:

  • Hyaline cartilage: Connects ribs to the sternum.

  • Articular cartilage: Found at the ends of long bones to facilitate smooth movement.

Joints (Articulations)

• Definition: Where two bones meet.

• Examples:

  • Shoulder joint: Humerus meeting the scapula.

  • Sagittal suture: The junction between the frontal and parietal bones.

Structure of the Skeleton

• The human skeleton comprises 206 bones divided into two major sections:

Axial Skeleton

• Components: Skull, vertebral column, and ribs.

Appendicular Skeleton

• Components: Pectoral girdle (shoulder, clavicle) and pelvic girdle (hips).

• Includes the bones of the arms and legs.

Total Bone Count

• 206 bones consist of:

  • 100 external surface bones

  • 6 additional bones in the ears (3 malleus, 3 stapes, and incus).

Functions of Bones

1. Support: Provides structure to the body.

2. Leverage: Bones act as levers to enhance movement (e.g., length of arms in arm wrestling).

3. Protection: Shields vital organs like the brain (by the cranium) and heart/lungs (by the thoracic cage).

4. Movement: Enables locomotion as muscles pull against bone structure.

5. Calcium Reserve: Bones store calcium and phosphate; depletion occurs during deficiency.

6. Blood Cell Formation: Red marrow in long bones produces blood cells, primarily located in the epiphysis.

Types of Osseous Tissue

Compact Bone

• Characteristics: Very dense and tightly mineralized; contains no hollow spaces.

• Composition: Two-thirds mineralized matrix of calcium phosphate.

Cancellous Bone (Spongy Bone)

• Characteristics: Has many open spaces, creating a spongy structure.

• Functions:

  • Site for red marrow and blood cell production.

  • Provides structural support—akin to cross bracing in structures like the Eiffel Tower.

Bone Aging and Health

• Aging effects: Osteopenia leads to loss of spongy bone and trabecular structures.

• Trabeculae: Small spicules of bone tissue that make cancellous bone strong and supportive.

Experiments with Bone Tissue

• Experiment: Place bone in vinegar for 3-5 days to observe changes.

  • Outcome: Bone becomes pliable as minerals are leached away.

• Composition of Bone: Mainly hydroxyapatite (calcium phosphate), which contributes to bone's hardness.