Skeletal System Overview

General Functions of the Skeleton

The skeletal system provides the structural framework for the body and serves several essential physiological functions.

• Movement: Bones act as attachment sites for skeletal muscles, soft tissues, and some organs. Muscle contraction exerts a pull on the skeleton, functioning as a system of levers to produce movement.

• Hemopoiesis: Blood cell production occurs in red bone marrow, a process known as hemopoiesis.

• Storage of Mineral and Energy Reserves: Bones store the body's reserve of calcium and phosphate, which can be released into the blood as needed. Calcium is essential for muscle contraction, blood clotting, and nerve impulse transmission. Lipids are stored in yellow bone marrow of adult bones.

Bone Structure and Types

Bone: Primary Organ of the Skeletal System

Bones form the rigid framework of the body and are classified based on their structure and function.

• Compact Bone: Also known as dense bone, it is composed of relatively dense connective tissue, appears white, smooth, and solid, and accounts for approximately 80% of bone mass.

• Spongy Bone: Also called cancellous or trabecular bone, it is located internal to compact bone, appears porous (often containing red bone marrow), and makes up about 20% of bone mass.

Cartilage and Connective Tissues

Types and Functions of Cartilage

Cartilage is a semirigid connective tissue that is more flexible than bone and serves various structural and functional roles.

• Hyaline Cartilage: Attaches ribs to sternum, covers ends of some bones, and is present within growth plates.

• Fibrocartilage: Weight-bearing cartilage that withstands compression, found in intervertebral discs, pubic symphysis, and cartilage pads of knees.

• Ligaments: Anchor bone to bone.

• Tendons: Connect muscle to bone.

Distribution of Cartilage in Adult and Juvenile Skeletons

Cartilage is distributed throughout the skeleton, with hyaline cartilage found at articular surfaces and growth plates, and fibrocartilage present in areas requiring resistance to compression.

Classification of Bones

Bone Shapes and Examples

Bones are classified according to their shapes, which relate to their functions and locations in the body.

• Long Bones: Greater in length than width, with an elongated, cylindrical shaft (diaphysis). Most common bone shape, found in upper and lower limbs (e.g., femur, humerus).

• Short Bones: Length nearly equal to width (e.g., carpal bones, tarsals, sesamoid bones, patella).

• Flat Bones: Flat, thin surfaces, may be slightly curved. Provide surfaces for muscle attachment and protect underlying soft tissues. Locations include the roof of the skull, scapulae, sternum, and ribs.

• Irregular Bones: Complex shapes (e.g., vertebrae, ossa coxae, ethmoid, sphenoid).

Classification of Bone by Shape (Visual Reference)

Illustrations typically show examples of each bone type in the human skeleton, such as the femur (long bone), tarsal (short bone), frontal bone (flat bone), and vertebra (irregular bone).

Gross Anatomy of Long Bones

Regions of a Long Bone

Long bones have distinct anatomical regions, each with specific structural and functional roles.

• Diaphysis: Elongated, usually cylindrical shaft.

• Medullary Cavity: Central cavity within the diaphysis, often containing bone marrow.

• Epiphysis: Expanded ends of the bone; includes proximal and distal epiphyses.

• Metaphysis: Region of mature bone between the diaphysis and epiphysis.

• Epiphyseal Plate: Growth plate found in children and adolescents; site of bone lengthening.

• Articular Cartilage: Hyaline cartilage covering the ends of bones at joints, reducing friction and absorbing shock.

Summary Table: Bone Types and Features

Key Terms and Definitions

• Hemopoiesis: The process of blood cell formation, occurring in red bone marrow.

• Diaphysis: The shaft of a long bone.

• Epiphysis: The end part of a long bone, initially growing separately from the shaft.

• Metaphysis: The region between the diaphysis and epiphysis, containing the growth plate.

• Articular Cartilage: Cartilage covering the articular surfaces of bones within a joint.

• Compact Bone: Dense bone tissue forming the outer layer of bones.

• Spongy Bone: Porous bone tissue found inside bones, often containing red bone marrow.

• Ligament: Connective tissue that connects bone to bone.

• Tendon: Connective tissue that connects muscle to bone.

Example Application

When a muscle contracts, it pulls on the bone to which it is attached via a tendon, resulting in movement at a joint. The bones involved are classified according to their shape and structure, which determines their function and location in the body.

Additional info: These notes provide foundational knowledge for understanding the anatomy and physiology of the skeletal system, including bone classification, structure, and the roles of cartilage, ligaments, and tendons.