Bone Tissue: Structure, Function, and Classification

Bone Tissue

Overview of the Skeletal System

The skeletal system is composed of bones and associated tissues, providing the framework for the human body. It includes the axial skeleton (skull, vertebral column, and rib cage) and the appendicular skeleton (limbs and girdles).

• Bones of the Skeleton & Spine: The skeleton consists of various bones, including the cranium, mandible, vertebrae, ribs, scapula, radius, ulna, femur, and pelvis. The vertebral column supports the trunk and protects the spinal cord.

Functions of the Skeleton

Major Roles of Bone Tissue

Bones serve several vital functions in the body, contributing to both structure and physiology.

• Support: Bones such as limb bones and vertebrae support the body’s weight; jaw bones support teeth; some bones support vital organs.

• Protection: Bones protect the central nervous system (CNS), heart, lungs, and other internal organs from injury.

• Movement: Bones act as levers for muscles, enabling movement and locomotion.

• Electrolyte Balance: Bones store calcium and phosphate ions, helping regulate their levels in the blood.

• Acid-Base Balance: Bones buffer the blood by absorbing or releasing phosphate and carbonate salts.

• Hematopoiesis: Blood cell production occurs in the red bone marrow found within certain bones.

Bones & Tissues

Composition of Bone Tissue

Bones are organs made up of several types of tissues, each contributing to their structure and function.

• Osseous Tissue: The main connective tissue of bone, with a matrix hardened by calcium and other minerals.

• Bone Marrow: Soft tissue within bones responsible for blood cell production.

• Blood: Present within bone marrow and vessels.

• Hyaline Cartilage: Covers joint surfaces and forms the initial template for bone development.

• Adipose Tissue: Fat storage, especially in yellow marrow.

• Nervous Tissue: Nerves within bones detect pain and regulate blood flow.

• Fibrous Connective Tissue: Forms the periosteum and endosteum, covering and lining bones.

Bone Classifications by Shape

Types of Bones Based on Shape

Bones are classified according to their shapes, which relate to their functions.

• Flat Bones: Thin, curved plates that protect soft organs. Examples: skull bones, ribs.

• Long Bones: Longer than they are wide; crucial for movement. Examples: arm and leg bones (femur, humerus).

• Short Bones: Approximately equal in length and width; allow for gliding movements. Examples: wrist (carpal) and ankle (tarsal) bones.

• Irregular Bones: Complex shapes that do not fit other categories. Examples: vertebrae, pelvic bones.

• Sesamoid Bones: (Additional info: Small bones embedded within tendons, such as the patella.)

Bone Anatomy & Terms

Structure of a Long Bone

Long bones have distinct anatomical regions and specialized tissues.

• Epiphysis: The expanded ends of a long bone (proximal and distal), containing spongy bone and red marrow.

• Diaphysis: The shaft of the bone, composed mainly of compact bone and containing the medullary cavity.

• Medullary Cavity: Central cavity within the diaphysis, filled with yellow marrow in adults.

• Articular Cartilage: Layer of hyaline cartilage covering joint surfaces to reduce friction.

• Periosteum: Dense fibrous membrane covering the outer surface of bones, containing nerves and blood vessels.

• Endosteum: Thin membrane lining the medullary cavity, involved in bone growth and remodeling.

• Compact Bone: Dense outer layer providing strength and protection.

• Spongy Bone: Porous inner layer found at the ends of long bones, containing red marrow.

Summary Table: Bone Classifications

Type	Shape	Main Function	Examples
Flat Bones	Thin, curved	Protection	Skull, ribs
Long Bones	Longer than wide	Movement	Femur, humerus
Short Bones	Equal length & width	Gliding	Carpals, tarsals
Irregular Bones	Complex shapes	Varied	Vertebrae, pelvis
Sesamoid Bones	Small, round	Embedded in tendons	Patella

Key Terms

• Osseous Tissue: Bone tissue, a type of connective tissue with a mineralized matrix.

• Periosteum: Outer fibrous covering of bone.

• Endosteum: Inner lining of bone cavities.

• Epiphysis: End part of a long bone.

• Diaphysis: Shaft of a long bone.

• Articular Cartilage: Cartilage covering joint surfaces.

Example

The femur is a classic example of a long bone, with a diaphysis (shaft), two epiphyses (ends), a medullary cavity filled with yellow marrow, and articular cartilage covering the joint surfaces.

Additional info: The study notes above expand on the provided slides and images, adding definitions, examples, and a summary table for clarity and completeness.