Lecture Notes: Bone Formation

Overview

Previous discussions on bone features:
- Micro anatomy of bone tissue
- Differences between spongy and compact bone
- Bone cells

Two main processes:
- Intramembranous ossification
  - Focus of current discussion
- Endochondral ossification
  - To be discussed later

Definition:
- "Intra" means from the inside, "membranous" means from a membrane
- Bone forms from a flat sheet of tissue
Learning Objectives:
- Describe intramembranous and endochondral ossification processes
- Reference pages 208-209 in Saladin
- Understand overall process rather than step-by-step details
Bones Formed by Intramembranous Ossification:
- Flat bones of the skull
- Parts of the mandible
- Parts of the clavicle

Start with embryological tissue (mesenchyme):
- Flat and resembles connective tissue
Cell Aggregation:
- Mesenchymal cells aggregate and transform into osteoblasts
- Osteoblasts are bone-building cells secreting bone matrix
Matrix Secretion and Calcification:
- Osteoblasts secrete matrix around themselves among blood vessels
- Matrix calcifies with deposition of hydroxyapatite (calcium compounds)
- Osteoblasts become trapped, transform into osteocytes, residing in lacunae
Growth of Ossification Center:
- Continued secretion by osteoblasts around perimeter
- Center expands, pushing out features like blood vessels
Development of Spongy Bone:
- Merging of ossification centers to form trabeculae
- Spongy bone has a honeycomb structure
Replacement and Remodeling:
- Blood vessels degenerate, spaces filled with red bone marrow
- Formation of compact bone layer around spongy bone
- Periosteum formation for potential bone growth in width

Description:
- Connective tissue transforms into bone tissue
- Results in non-functional, extraneous bone formation
Symptoms and Diagnosis:
- Painful, non-curable condition
- X-ray shows abnormal bone structures outside skeleton
- Features of bones exaggerated and abnormal