CHAPTER 6

Types of Bones

I. Irregular Bones

  • Complex shapes that do not fit into other categories.

  • Provide protection and support for various organs.

  • Examples:

    • Vertebrae: Protecting the spinal cord while also allowing for flexibility and movement of the torso.

    • Sacrum: Connects the spine to the pelvis, providing support for the upper body and stability while standing or walking.

    • Facial bones: Shape the face and protect organs related to sight (orbital bones), smell (nasal bones), and taste (mandible and maxilla).

II. Short Bones

  • More round than long, offering stability and support with some movement.

  • Structure includes a thin layer of compact bone surrounding a larger volume of spongy bone, ensuring light weight and strength.

  • Examples:

    • Carpals (wrist): Consist of eight bones that facilitate a wide range of wrist movements while providing stability.

    • Tarsals (ankle): Composed of seven bones that contribute to foot stability and mobility, allowing for various movements while bearing weight.

III. Long Bone Structure

  • Example: Femur

    • The longest bone in the body that transmits weight from the upper body to the lower limbs and provides leverage for movement.

    • Vital for activities such as walking, running, and jumping due to its strength and structural integrity.

A. Cross-Section Analysis

  • Prominent Features:

    • Volkmann's Canals: Channels that allow for the passage of blood vessels and nerves, connecting the periosteum to the central Haversian canals.

    • Osteons: The basic structural unit of compact bone, consisting of concentric lamellae of bone matrix that surround a central canal containing blood vessels and nerves. This structure facilitates nutrient and waste exchange throughout the bone tissue.

IV. Bone Development

  • Starts with osteoprogenitor cells located in the periosteum (outer layer of bone) and endosteum (inner layer).

  • These cells differentiate into osteoblasts which synthesize new bone tissue by producing collagen and other proteins. Once surrounded by the bone matrix they become osteocytes, which are responsible for maintaining tissue homeostasis, sensing mechanical strain, and regulating bone remodeling processes.

V. Inhibition of Osteoblast Activity

  • Crucial for calcium balance in the blood, as osteoblasts are responsible for bone formation.

  • A decrease in pH (acidosis) inhibits osteoblast activity, which can lead to lower calcium deposition in bones and higher calcium levels in the blood, affecting essential bodily functions such as muscle contraction and nerve signaling.

VI. Summary

  • Understanding bone types and structures is vital for studying the skeletal system:

    • Long bones like the femur are crucial for mobility, support, and weight-bearing.

    • Irregular and short bones contribute to stability, protection, and overall health, serving specific functions essential for daily activities and movement.