Bone Tissue & Skeletal System: Structure, Function, and Classification

Bone Tissue & Skeletal System

Introduction

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

The Skeletal System

Major Divisions

• Axial Skeleton: Consists of the head, neck, and trunk. It includes the skull, vertebral column, and rib cage.

• Appendicular Skeleton: Comprises the upper and lower limbs, as well as the pectoral (shoulder) and pelvic girdles.

Components:

• Bones of the skeleton

• Cartilages

• Ligaments

• 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.

• The hardness is due to mineralization, primarily with calcium phosphate.

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 bones/carpals, ankle bones/tarsals).

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

• Irregular Bones: Complex shapes; examples include vertebrae and 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: Classification of Bones by Shape

Type	Shape	Examples
Long Bones	Long and thin	Humerus, femur, phalanges
Short Bones	Cube-shaped	Carpals, tarsals
Flat Bones	Thin, flat, parallel surfaces	Skull, sternum, ribs, scapula
Irregular Bones	Complex shapes	Vertebrae, pelvic bones
Sesamoid Bones	Small, round, develop in tendons	Patella
Sutural Bones	Small, irregular, in skull sutures	Wormian bones

Additional info:

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

• Histological classification (compact vs. spongy bone) will be covered in detail in subsequent sections.