Classification and Anatomy of Bones

Study Notes

Classification of Bones

Long bones: Longer than wide, with a shaft (diaphysis) and ends (epiphyses). Examples: femur, humerus.
Short bones: Cube-shaped, mostly spongy bone. Examples: carpals, tarsals. Sesamoid bones are short bones formed within tendons, like the patella.
Flat bones: Thin, flattened, and usually curved. Two layers of compact bone surround spongy bone. Examples: skull, ribs, sternum.
Irregular bones: Irregular shape, don't fit into other categories. Examples: vertebrae, hip bones.

Anatomy of a Long Bone

Diaphysis: Shaft of the bone, composed of compact bone.
Epiphysis: Ends of the bone, composed of spongy bone.
Articular Cartilage: Covers the epiphyses, reduces friction in joints.
Epiphyseal Plate: Growth region in young bones, responsible for lengthwise growth.
Epiphyseal Line: Remnant of the epiphyseal plate in adults, marking where growth stopped.
Medullary Cavity: Center of the diaphysis, contains yellow marrow in adults and red marrow in infants.
Periosteum: Membrane surrounding the outer surface of the bone, contains perforating (Sharpey's) fibers that attach it to the bone.

Key Functions of the Skeletal System

Support: Provides structure and shape to the body.
Protection: Protects internal organs, like the brain, spinal cord, and thoracic cavity organs.
Movement: Facilitates movement through attached muscles.
Storage: Stores calcium and phosphorus, and fat in the medullary cavity.
Blood Cell Formation (Hematopoiesis): Produces blood cells within the bone marrow.

Components of the Skeletal System

Bone (Skeleton): The primary structural component.
Cartilage: Reduces friction in joints and serves as a model for bone formation.
Tendons: Attach bone to muscle.
Ligaments: Attach bone to bone.

Bone Formation (Ossification)

Definition: Process of bone formation, primarily occurring in utero.
Osteoblast's Role: Cells responsible for building bone by secreting bone matrix. Once surrounded by matrix, they become osteocytes.
Ossification Centers: Starting points of bone formation.
- Primary Ossification Center: First area where bone appears, forms the diaphyses.
- Secondary Ossification Center: Forms the epiphyses.

Types of Bone Tissue

Compact Bone: Dense and solid, forms the outer layer of bones.
Spongy (Cancellous) Bone: Porous, contains many spaces filled with red marrow, found in the interior of bones.

Extracellular Matrix Composition

Bone: Collagen and minerals, providing flexibility and weight-bearing capacity.
Cartilage: Collagen and proteoglycans, responsible for shock absorption and smooth surface.
Tendons and Ligaments: Collagen, providing exceptional toughness.

Skeleton Structure

The adult skeleton is composed of 206 bones.
Divided into two subdivisions:
- Axial Skeleton: Includes skull, vertebral column, and rib cage.
- Appendicular Skeleton: Includes limbs, pectoral girdle, and pelvic girdle.

Appendicular Skeleton

Composed of 126 bones.
Includes:
- Limbs (appendages)
- Pectoral girdle (shoulder bones)
- Pelvic girdle (hip bones)

Summary

The skeletal system plays a crucial role in providing support, protection, and movement for the body. Understanding its components, classifications, and bone formation processes is essential for appreciating its importance in human biology.