lecture 13 pt1

Bone Marrow and Blood Cell Production

• Bone Structure

  • Importance of bone marrow in blood production.

  • Medullary Cavity: central cavity of bone where bone marrow resides.

  • Red Bone Marrow: responsible for producing blood cells, primarily found in the long bones during childhood.

• Transition in Blood Production

  • Fetal Stage: blood production occurs in the liver before bones are formed.

  • After birth: shift of blood production from liver to long bones (e.g., arms and legs) as red bone marrow forms.

  • As individuals age, blood production shifts from long bones to flat bones (ribs, pelvis, scapula, skull) to prevent anemia if limbs are lost.

  • Flat bones are not fully formed at birth, resulting in the shift in blood production sites as they mature.

  • Marrow Transplant: Usually taken from flat bones like the hip due to high red bone marrow concentration.

• Yellow Bone Marrow: As one ages, red bone marrow can convert to yellow marrow (fatty).

• Pulse Check in Broken Bones: Importance of checking circulation before and after a break to avoid complications from fat embolism.

Bone Formation

• Types of Ossification: Two primary processes involved in bone development.

1. Intermembranous Ossification

• Definition: Bone formation occurring between two layers of membranes, primarily for flat bones.

• Formation Process:

  • Development starts with connective tissue membranes where blood vessels bring osteoblasts (cells responsible for bone formation).

  • Osteoblasts: Producing bone matrix and hardening membranes into solid bone, known as compact bone.

  • Creation of trabeculae: calcified bone fibers within the spongy bone (cancellous bone).

  • Forms flat bones like the skull, ribs, and hips, culminating in the filling of spaces with red bone marrow.

2. Endochondral Ossification

• Definition: Conversion of cartilage to bone, the primary process for long bones.

• Initial Structure: Entire skeleton laid out in hyaline cartilage during fetal development.

• Process:

  • Blood vessels target the diaphysis (shaft) of the bone, depositing osteoblasts that begin converting cartilage to bone spicules.

  • Resulting layers create compact bone on the exterior and spongy bone in the interior.

  • Perichondrium: membrane surrounding cartilage; changes to periosteum as bone forms.

  • Ends of bones have epiphyseal plates which produce cartilage, controlled by growth hormones, impacting bone growth.

Interactions of Bone Cells

• Bone Cells: Three main types with distinct functions.

  • Osteoblasts: Produce new bone.

  • Osteocytes: Maintain bone health.

  • Osteoclasts: Reabsorb bone, crucial for creating the medullary cavity and strengthening bone structure.

• Bone Repair:

  • In the event of a fracture, cartilage initially fills the break before osteoblasts convert this cartilage back to bone over time.

  • A properly set fracture usually results in a stronger site than surrounding bone due to the bone formation process.

Bone Structure and Functionality

• Bone features such as bumps and grooves indicative of muscle and tendon attachment  Sharpie’s fibers anchor connective tissues.

• Wolff's Law:

  • States that bone is created in response to the direction of force and is dissolved where opposing force exists.

  • Exercising enhances bone structure, leading to adaptations in response to increased load.

• Variations in exercise levels are visible on skeletal remains, indicating muscle use and bone adaptations.

Application and Relevance in Dental Orthodontics

• Braces and Bone Remodeling: Forces applied by braces lead to bone dissolution and formation as teeth shift.

  • Retainers aid in stabilizing teeth until bone fully adapts after brace removal, preventing reversion.

• Ideal timing for orthodontic intervention can vary, with certain ages best suited for efficient bone remodeling.