Bone Tissue & Skeletal System

Introduction

The skeletal system is a fundamental component of the human body, providing structure, protection, and support. It is composed of bones, cartilage, ligaments, and other connective tissues that stabilize and connect the body’s framework.

The Skeletal System

Main Divisions of the Skeleton

• Axial Skeleton: Includes the head, neck, and trunk. It forms the central axis of the body and consists of the skull, vertebral column, and rib cage.

• Appendicular Skeleton: Comprises the upper and lower limbs, as well as the pectoral (shoulder) and pelvic girdles. These structures facilitate movement and interaction with the environment.

Components:

• Bones of the skeleton

• Cartilages

• Ligaments and other connective tissues

Functions of the Skeletal System

• Support: Maintains and supports body stature.

• Protection: Shields internal vital organs such as the brain and heart.

• Attachment: Forms the skeleton, providing attachment points for tendons and muscles.

• Movement: Facilitates movement by serving as levers for muscles.

• Metabolic Function: Acts as a reservoir for calcium (Ca2+ homeostasis) and other minerals.

• Blood Cell Production: Contains marrow cavities that house hemopoietic (blood-forming) tissue.

Bone (Osseous) Tissue

Definition and Properties

• Bone tissue is a type of supporting connective tissue in which the matrix is modified to be hard and tensile.

• This unique composition allows bones to withstand compressive forces and provide structural integrity.

Classification of Bones

Criteria for Classification

• Shape

• Bone markings

• Internal microscopic appearance (Histology)

Bone Shapes

• Long Bones: Longer than they are wide; found in arms, legs, hands, feet, fingers, and toes (e.g., humerus, femur).

• Short Bones: Approximately equal in length and width; cube-shaped (e.g., wrist and ankle bones).

• Flat Bones: Thin and flat with parallel surfaces; found in the skull, sternum, ribs, and scapula.

• Irregular Bones: Complex shapes that do not fit other categories (e.g., vertebrae, pelvic bones).

• Sesamoid Bones: Small and flat, develop inside tendons near joints (e.g., patella).

• Sutural (Wormian) Bones: Small, irregular bones found between the flat bones of the skull.

Bone Markings

• Depressions or grooves: Along bone surfaces, often for passage of blood vessels or nerves.

• Projections: Where tendons and ligaments attach or at articulations with other bones.

• Tunnels: Openings where blood vessels and nerves enter bone.

Example Table: Comparison of Axial and Appendicular Skeleton

Additional info:

• Bone markings are essential for understanding muscle attachment and joint articulation.

• Histological classification (compact vs. spongy bone) is covered in more detail in subsequent sections.