The Skeletal System Overview

The Skeletal System

• At birth, the human body has approximately 300 bones.
• During growth, some bones fuse together, resulting in 206 bones in an adult.
• Bone size and shape differ depending on location in the body.

Bone Types

• Flat Bones: Thin and flat, like the shoulder blade (scapula) and skull bones.
• Long Hollow Bones: Found in the arms, legs, and fingers.
• Cylindrical Bones: Such as the vertebrae.
• Irregular Bones: Bones in the wrist and ankle.
• Other Bones: Ribs, etc.

Functions of Bone

• Support: Provides structural framework, especially in the legs. Muscles are attached to bones via tendons and ligaments.
• Locomotion: Bone joints allow movement.
• Protection: The skull protects the brain and sensory organs (eyes, ears). Ribs form a cage to protect the heart and lungs.
• Storage: Bones store minerals like calcium (Ca), released as needed.
• Nourishment: Teeth, specialized bones, help break down food, aiding in nourishment.
• Sound Transmission: The ossicles in the middle ear, the smallest bones, transmit sound vibrations from air to the fluid in the cochlea.

Bone Remodeling

• Bone is a living tissue with a blood supply and nerves.
• Osteocytes: Cells that maintain bone health, accounting for 2% of bone volume.
• Bone undergoes constant remodeling throughout life.
• Bone Remodeling: A continuous process of destroying old bone (by osteoclasts) and building new bone (by osteoblasts).
• This process replaces the entire skeleton approximately every seven years.
• Osteoclasts break down bone daily, releasing about 0.5 grams of calcium (from a total of 1000 grams in the skeleton). Osteoblasts rebuild using a similar amount of calcium.

Composition of Bone

• Bone is composed of two main materials plus water.
• Collagen: The major organic component, about 40% of bone weight and 60% of its volume.
  • Provides flexibility and tensile strength.
  • Bone becomes fragile without collagen.
  • Produced by osteoblasts.
• Bone Mineral (Inorganic Component): About 60% of bone weight and 40% of its volume.
  • Calcium hydroxyapatite (Ca10(PO4)6(OH)2) adds rigidity to bone.

Bone Strength

• Solid (Compact) Bone: Found in the central shaft of long bones.
• Spongy (Cancellous) Bone: Composed of thin, thread-like trabeculae (trabecular bone). Located at the ends of long bones.
  • Weaker than compact bone due to less bone material in a given volume.
  • Advantages over compact bone:
    • Greater strength with less material in areas under compressive force (ends of bones, spine).
    • Flexibility to absorb energy during activities like walking, running, and jumping.

Stress and Strain

• Stress (S): The internal force per unit area acting on a material. S = F/A (F = force, A = area).
• Longitudinal Strain (St): The fractional change in length due to applied force. St = ∆L/L (∆L = change in length, L = original length).

Hooke's Law

• Robert Hooke observed that within the elastic limit, the ratio of stress to strain is constant (Hooke's Law).
  • Y = S/St (Y = Young's modulus).
  • Y = (L F) / (A ΔL).
• When tension or compression is applied to bone, its length changes.

Young's Modulus of Elasticity

• The ratio of stress to strain in the initial linear portion of the stress-strain curve is called Young's modulus (Y).

Explore the fascinating aspects of the human skeletal system, from the number of bones at birth to the types and functions of various bones in the adult body. This quiz will test your knowledge on bone structure, types, and their important roles in support, locomotion, protection, and storage.