Skeletal System Notes

Functions of the Skeletal System

  • Support/Structure: Provides upright posture and structure to the body.

  • Movement: Serves as an attachment point for skeletal muscles, facilitating movement.

  • Protection: Encases and protects vital organs.

  • Mineral Storage: Primarily stores calcium, along with phosphorus, sodium, and potassium.

  • Blood Cell Formation: Hematopoiesis occurs in the red marrow found in certain bones.

Characteristics of Bone Tissue

  • Dynamic Nature: Bones are living connective tissues that are active and undergo constant change, not static.

Classification of Bones by Shape

  1. Long Bones:

    • Description: Long, with longitudinal axes and expanded ends.

    • Examples: Femur (thigh bone), humerus (upper arm).

  2. Short Bones:

    • Description: Cube-shaped.

    • Examples: Carpals in the wrist, tarsals in the ankle.

  3. Flat Bones:

    • Description: Platelike with broad surfaces.

    • Examples: Ribs, scapulae, parietal bone of the skull.

  4. Irregular Bones:

    • Description: Variety of shapes; do not fit into other categories.

    • Examples: Vertebrae, some facial bones.

  5. Sesamoid Bones:

    • Description: Small, nodular; embedded in tendons.

    • Example: Patella (kneecap).

Parts of a Bone

  • Epiphysis:

    • Expanded ends that articulate with other bones and are coated with articular (hyaline) cartilage.

  • Diaphysis:

    • Central long shaft located between the epiphyses.

  • Periosteum:

    • Dense connective tissue covering the bone except where articular cartilage is present; facilitates growth and repair, containing osteoblasts and blood vessels.

  • Medullary Cavity:

    • Hollow space in the diaphysis filled with yellow marrow for energy storage; can convert to red marrow as needed.

    • Lined by endosteum.

Types of Bone Tissue

  • Compact Bone:

    • Dense and strong; makes up the diaphysis walls and covers the outer surface of epiphyses.

  • Spongy Bone:

    • Contains a network of tiny, interconnecting plates; primarily located in the epiphyses and contains red marrow.

Microscopic Structure of Bone

  • Types of Bone Cells:

    • Osteoblasts: Youthful cells responsible for building bone tissue, secreting the bone matrix called mesenchyme.

    • Osteocytes: Mature cells that maintain bone matrix; produce less mesenchyme and are encapsulated in lacunae.

    • Osteoclasts: Large cells that break down bone tissue by secreting acids and enzymes to dissolve the matrix.

Summary of Bone Cells

  • Canaliculi: Tiny channels connecting osteocytes.

  • Matrix: The intercellular substance in which bone cells are embedded.

  • Osteoprogenitor Cells: Stem cells that can differentiate into osteoblasts.

Important Reminder

  • Quiz Tomorrow: Review all the above information thoroughly to prepare for the exam!