The Skeletal System: Functions and Components

• The skeletal system provides structure and shape to the body.
• It consists of bones and connective tissues, including cartilage, tendons, and ligaments.
• Bone growth, development, and remodeling are essential biological processes for the skeletal system.

Functions

• Movement: Muscles attach to bones via tendons (fibrous connective tissue).
• Support: The backbone supports the upper body and maintains posture.
• Protection: The skeletal system acts as a protective shield for internal organs.
  • Skull protects the brain.
  • Rib cage protects the lungs and heart.
• Blood Production (Hematopoiesis): Red and white blood cells are formed in bone marrow.
  • Bone marrow is located in long bones (femur, humerus) and flat bones (sternum, pelvis).
• Storage: Bones store minerals like calcium and phosphorus.
  • These stored minerals are essential for bone health, muscle function, nerve signaling, muscle contraction, blood clotting, and maintaining pH balance.
  • The skeletal system also stores smaller amounts of magnesium, sodium, potassium, and fluoride.

Parts

• Bones are hard, rigid organs composed of dense connective tissue, collagen fibers, and mineral deposits.
  • Bones provide structural support, organ protection, mineral storage, and blood cell production.
• Joints are areas where bones meet, allowing movement relative to each other.

Types of Joints

• Fibrous: Immovable joints held together by fibrous connective tissue.
  • Example: sutures connecting skull bones, allowing expansion to accommodate brain size.
• Cartilaginous: Slight movement joints connected by cartilage.
  • Example: joints between vertebrae (intervertebral discs).
• Synovial: Full movement joints with a synovial cavity filled with lubricating fluid.
  • Examples: knee, elbow, and shoulder joints.
• Cartilage is a specialized connective tissue made of chondrocytes.
  • Chondrocytes are responsible for maintenance and repair.
  • Cartilage provides structural support, joint cushioning, flexibility, and smooth joint movement.
• Ligaments are tough fibrous bands.
  • Ligaments provide stability, support, and protection to joints.
  • They regulate joint movement and prevent injuries.

Basic Bone Shapes

• Long: Elongated shape found in arms, legs, and fingers (e.g., femur, humerus).
  • Shaft (Diaphysis): the long part.
  • Epiphyses: two round ends.
• Short: Cube or box shape found in wrists (carpals) and ankles (tarsals).
  • Composed of cancellous or spongy bone tissue covered by compact bone.
• Flat: Flattened, thin, and firm, found in the skull (cranial bones) and sternum (breast bone).
  • Sandwiching of two compact bone layers with one spongy bone layer.
• Irregular: Complex shape found in the spine or vertebral column.
  • Composed of compact and spongy bone

Layers of Bone

• Periosteum: The outermost covering of bone (except at joints).
  • It's a protective layer and the attachment point for tendons and ligaments.
• Compact Bone: Located under the periosteum, also known as cortical bone.
  • Dense, hard, with small canals for blood vessels and nerves.
  • Provides strength and support, resisting bending and compression.
• Spongy Bone: Located under compact bone, also known as trabecular/cancellous bone.
  • Found at the end part of bones
  • Lightweight but strong with holes and small spaces.
  • Contains red bone marrow for the production of red blood cells, white blood cells, and platelets.

Bone Marrow

• Bone marrow is a gelatinous tissue filling the gaps in spongy bone.
• Red Marrow: Responsible for blood cell production, especially in children.
• Yellow Marrow: Composed of fat for energy storage; more prevalent in adults.
  • Red marrow is limited to flat bones and the ends of long bones in adults.
  • Yellow marrow can convert to red marrow in cases of anemia or blood loss.
• Medullary Cavity: hollow central space located in the shaft.
  • Contains red and yellow bone marrow.
  • Lined with a thin membrane (endosteum) made of osteoblasts and osteoclasts.
  • Surrounded by compact bone.

Bone Strength

• Bones are lightweight and strong due to their porous structure.
• Bones make up approximately 20% of body weight.
• Bones are composed of calcium (for bone formation, growth, and remodeling) and phosphorus (for mineralization, energy metabolism, acid-base balance, and cellular function).