Anatomy of Osseous Tissue

Review of Bone Anatomy

Key Components of Long Bones
- Parts of a Long Bone
- Diaphysis:
  - Definition: The long central shaft of the bone.
- Metaphysis:
  - Definition: The region where the diaphysis meets the epiphysis.
- Epiphyseal Plate:
  - Definition: The growth plate at the end of long bones, where lengthening occurs.
  - Composition: Made up of hyaline cartilage.
  - Transition: Turns into the epiphyseal line when growth ceases, indicating the cartilage has been replaced by bone.
Diaphysis Composition:
- Type of Bone: Composed of compact bone.
- Function: Provides support and withstands weight.
- Medullary Cavity:
- Definition: The hollow region within the diaphysis.
- Function: Storage of yellow marrow.
Epiphysis Composition:
- Type of Bone:
- Outside: Compact bone.
- Inside: Spongy bone.
- Blood Vessels: Form from spaces in the spongy bone, leading to the formation of red marrow, the site of hematopoiesis (blood cell production).

Hematopoiesis:
- Definition: The production of formed elements of blood; involves erythropoiesis (red cells), leukopoiesis (white cells), and thrombopoiesis (platelets).
Articular Cartilage:
- Definition: Hyaline cartilage that covers epiphyses, providing a smooth surface for articulation of bones.
Endosteum:
- Definition: Thin membrane lining the medullary cavity.
Periosteum:
- Definition: Tough, outer fibrous membrane surrounding the diaphysis.
- Contains: Blood vessels, nerves, lymphatic vessels.
- Note: Covers only the diaphysis, not the epiphyses.
Bone Markings:
- Foramen: A hole in the bone.
- Matus: An opening into a canal.
- Fissure: A jagged opening in the bone.
- Process: A projection from the bone surface.
- Protuberance: A large rounded projection.

Osteocytes:
- Definition: Mature bone cells responsible for maintaining bone tissue.
- Location: Found in lacunae, which are small cavities in the bone.
Osteoblasts:
- Definition: Bone-forming cells that secrete collagen fibers and calcium salts.
- Function: Responsible for new bone formation.
- Transition: Mature into osteocytes when surrounded by bone matrix.
Osteoclasts:
- Definition: Cells that break down bone tissue (resorption).
- Origin: Differentiate from blood macrophages.
- Function: Responsible for the release of minerals (e.g., calcium) into the bloodstream.
Osteogenic Cells:
- Definition: Stem cells that can differentiate into osteoblasts.
- Function: Undergo mitosis and produce osteoblasts, maintaining a supply of bone-forming cells.

Cooperation Between Osteoblasts and Osteoclasts:
- Both cell types work together to reshape and remodel bone in response to stress.
- Example: Pressure from braces can lead to changes in the jawbone.
Stress Response:
- Increased mechanical stress (e.g., from weight-bearing activities) leads to adaptive bone remodeling.
- Lack of stress (e.g., during prolonged immobilization) can lead to decreased bone density.

Histology of Compact Bone:
- Composition: Dense arrangement with few cells.
- Structure: Comprised of Osteons (Haversian systems) with central canals housing blood vessels.
- Lacunae are located within lamellae (concentric circles of bone).
Perforating Canals:
- Connections between osteons, allowing for vascular and neural communication throughout bone tissue.
Spongy Bone Composition:
- Lattice-like structure that houses red marrow and is designed for lightness and strength.
- Functions differently in various bones depending on their role in weight support and movement.

Students are encouraged to review all components of bone anatomy covered in class, ensuring a strong understanding of both compact and spongy bone before moving on to their next topic.