The Skeletal System: Structure, Function, and Osseous Tissue

The Skeletal System

Introduction

The skeletal system is a fundamental organ system in the human body, providing structure, protection, and support for movement. It is composed of several interconnected components that work together to maintain bodily integrity and function.

• Skeletal bones: The rigid framework of the body.

• Cartilage: Flexible connective tissue found in joints and other areas.

• Ligaments: Bands of connective tissue that connect bones to other bones.

• Connective tissue: Stabilizes and supports the skeleton.

Bones are dynamic organs, consisting of several tissue types and capable of growth and repair throughout life.

Functions of the Skeletal System

Major Functions

The skeletal system performs several essential functions necessary for survival and health.

• Support: Provides the framework for the attachment of organs and tissues.

• Storage of minerals:

  • Calcium ions: Approximately 98% of the body's calcium is stored in bones.

  • Phosphate ions: Bones serve as a reservoir for phosphate, important for energy metabolism and cell signaling.

• Blood cell production: Bone marrow produces erythrocytes (red blood cells), leukocytes (white blood cells), and platelets (cell fragments involved in clotting).

• Leverage: Muscles pull on bones to produce movement, allowing locomotion and manipulation of the environment.

• Protection:

  • Ribs: Protect the heart and lungs.

  • Skull: Protects the brain.

  • Vertebrae: Protect the spinal cord.

  • Pelvic bones: Protect reproductive organs.

Structure and Function of Bone

Bones (Osseous Tissue)

Bones are a specialized form of supporting connective tissue, characterized by a solid matrix and specialized cells. They are covered and lined by distinct membranes that play roles in growth and repair.

• Specialized cells: Include osteocytes, osteoblasts, osteoclasts, and osteoprogenitor cells.

• Solid matrix: Provides strength and rigidity.

• Outer lining: Called the periosteum, which isolates and protects the bone.

• Inner lining: Called the endosteum, which lines the medullary cavity and is involved in bone growth and repair.

Histological Organization of Mature Bone

The mature bone matrix is a composite of inorganic and organic components, each contributing to the bone's mechanical properties.

• Inorganic component:

  • Calcium phosphate: The primary mineral in bone, which eventually converts to hydroxyapatite crystals.

  • Hydroxyapatite crystals: Make up approximately 65% of bone mass and provide resistance to compression.

• Organic component: (Additional info: Not shown in these slides, but includes collagen fibers and ground substance, which provide tensile strength and flexibility.)

Key Terms and Concepts

• Periosteum: A dense layer of vascular connective tissue enveloping the bones except at the surfaces of the joints.

• Endosteum: A thin vascular membrane lining the inner surface of the bony tissue that forms the medullary cavity.

• Hydroxyapatite: A naturally occurring mineral form of calcium apatite with the formula $Ca_{10}(PO_4)_6(OH)_2$.

Example: Bone Matrix Composition

• Inorganic: Hydroxyapatite crystals (calcium phosphate).

• Organic: Collagen fibers (provide tensile strength).

Additional info: The combination of hydroxyapatite and collagen makes bone both strong and flexible, allowing it to withstand various mechanical stresses.