Bones

• Bones are rigid organs that form part of the endoskeleton of vertebrates.
• They function to move, support, and protect the various organs of the body, produce red and white blood cells, and store minerals.
• Bone tissue is a type of dense connective tissue. Bones come in a variety of shapes and sizes and have a complex internal and external structure.

Composition and Properties of Bone

• Matrix Material:

  • Organic Components: Primarily collagen, which provides tensile strength and flexibility.
  • Inorganic Components: Primarily calcium phosphate, which provides hardness and resistance to compression.

• Bone Cells:

  • Osteoblasts: Cells responsible for bone formation.
  • Osteocytes: Mature bone cells that maintain the bone matrix.
  • Osteoclasts: Cells involved in the resorption of bone tissue.

Structure of Bone

• They are rigid connective tissue organs that make up the skeletal system.
• They are composed of specialized cells, extracellular matrix, and minerals.
• The structure of a bone can be divided into two parts: the macroscopic and microscopic structures.

Macroscopic Structure:

• Diaphysis:

  • The long, cylindrical portion of a long bone.
  • Composed primarily of compact bone, providing strength and rigidity.

• Epiphyses:

  • The rounded ends of a long bone.
  • Mostly made of spongy bone, with an outer layer of compact bone.

• Metaphysis:

  • The region between the diaphysis and epiphysis where bone growth occurs during childhood and adolescence.
  • Contains the epiphyseal plate (growth plate) in growing individuals.

• Periosteum:

  • A dense, fibrous membrane covering the outer surface of bones, except at joints.
  • Contains blood vessels, nerves, and osteogenic cells essential for bone growth, repair, and nutrition.

• Endosteum:

  • A thin, vascular membrane lining the inner surface of bones, including the medullary cavity and trabeculae of spongy bone.
  • Contains osteogenic cells involved in bone growth and repair.

• Medullary Cavity:

  • A hollow space within the diaphysis of long bones.
  • Filled with yellow bone marrow, which stores fat and serves as an energy reserve.

Microscopic Structure:

• Compact Bone:

  • Also known as cortical bone, it is dense and forms the outer layer of bones.
  • Consists of tightly packed concentric rings called lamellae, surrounding a central Haversian canal.
  • Haversian canals contain blood vessels and nerves, providing nutrients and oxygen to the bone cells.

• Spongy Bone:

  • Also known as cancellous or trabecular bone, found mainly in the epiphyses of long bones and the interior of other bones.
  • Consists of a network of interconnected trabeculae, creating a porous structure.
  • The spaces within spongy bone are filled with red bone marrow, where blood cell production occurs.

Functions:

1. Support: Bones provide a framework for the attachment of muscles and other tissues.
2. Protection: Bones such as the skull and rib cage protect vital organs from injury.
3. Movement: Muscles are attached to bones, which act as levers to produce movement.
4. Mineral Storage: Bones serve as a reservoir for minerals, particularly calcium and phosphorus.
5. Blood Cell Production: The marrow in the cavities of bones is the site of red blood cell production (hematopoiesis).

Bone Growth and Remodeling:

• Growth:

  • They grow in length due to activity at the epiphyseal plate (growth plate).
  • It grows in diameter through the addition of bone tissue at the surface.

• Remodeling:

  • A lifelong process where bone tissue is continuously replaced and reshaped.
  • Influenced by mechanical stress and hormonal changes.

Types of Bones

• Long:

  • Longer than they are wide, functioning as levers for movement.
  • Examples: Femur, tibia, fibula, humerus, radius, ulna.

• Short:

  • Cube-shaped, providing support and stability with little movement.
  • Examples: Carpals (wrist bones), tarsals (ankle bones).

• Flats:

  • Thin, flattened shape, protecting underlying organs or providing large surface areas for muscle attachment.
  • Examples: Skull bones, scapula, sternum, ribs.

• Irregular:

  • Complex shapes that fulfill various functions, such as protection and support.
  • Examples: Vertebrae, sacrum, coccyx, bones of the pelvis (ilium, ischium, pubis).

• Sesamoids:

  • Small, round bones embedded within tendons, helping to reduce friction.
  • Example: Patella (kneecap).

Health and Disease:

• Osteoporosis:

  • A condition characterized by decreased bone mass and increased susceptibility to fractures.

• Arthritis:

  • Inflammation of the joints, which can affect the surrounding bone structure.

• Fractures:

  • Breaks in the bone often caused by stress or impact.

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