Osseous Tissue and Bone Structure: Study Notes

Introduction to the Skeletal System

Overview of the Skeletal System

The skeletal system forms the structural framework of the human body and is essential for movement, protection, and various metabolic functions.

• Bones of the skeleton: The rigid organs that constitute the majority of the skeletal system.

• Cartilages, ligaments, and connective tissues: Support and connect bones, providing flexibility and stability.

Functions of the Skeletal System

Major Functions

The skeletal system performs several critical functions necessary for survival and homeostasis.

• Support: Provides structural support for the entire body.

• Storage of minerals: Bones store essential minerals, especially calcium and phosphorus, which are released into the bloodstream as needed.

• Storage of lipids: Yellow marrow stores lipids, serving as an energy reserve.

• Blood cell production: Red marrow produces red blood cells, white blood cells, and platelets (a process called hematopoiesis).

• Protection: Bones protect vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Leverage: Bones act as levers to facilitate movement by muscles.

Classification of Bones

Criteria for Classification

Bones are classified based on their shape, internal tissue organization, and surface features known as bone markings.

• Shape: The external form of the bone.

• Internal tissue organization: The arrangement of bone tissue within the bone.

• Bone markings: Surface features such as ridges, grooves, and openings that serve as attachment points or passageways.

Classification by Shape

Bones are grouped into several categories based on their shapes, each with distinct locations and functions.

• Long bones: Long and thin; found in arms, legs, hands, feet, fingers, and toes. Example: humerus.

• Flat bones: Thin with parallel surfaces; found in the skull, sternum, ribs, and scapulae. Example: parietal bone.

• Sutural bones: Small, irregular bones located between the flat bones of the skull.

• Irregular bones: Complex shapes; examples include spinal vertebrae and pelvic bones.

• Short bones: Small and thick; examples include bones of the ankle (tarsals) and wrist (carpals).

• Sesamoid bones: Small and flat; develop inside tendons near joints of knees, hands, and feet. Example: patella.

Classification by Bone Markings

Bones have various surface features that are important for their function and interaction with other tissues.

• Depressions or grooves: Found along bone surfaces; often serve as passageways for nerves and blood vessels.

• Projections: Sites where tendons and ligaments attach or where bones articulate with each other.

• Tunnels: Openings through which blood vessels and nerves enter the bone.

Summary Table: Bone Classification by Shape

Bone Type	Description	Examples
Long Bones	Long and thin	Humerus, femur, phalanges
Flat Bones	Thin, parallel surfaces	Skull, sternum, ribs, scapulae
Sutural Bones	Small, irregular	Between skull bones
Irregular Bones	Complex shapes	Vertebrae, pelvic bones
Short Bones	Small and thick	Carpals, tarsals
Sesamoid Bones	Small, flat, develop in tendons	Patella

Example: The Patella

The patella is a sesamoid bone located within the tendon of the quadriceps femoris muscle, providing protection and improving leverage for knee extension.

Additional info: Bone markings are essential for identifying anatomical landmarks and understanding the attachment and passage of muscles, tendons, nerves, and blood vessels.