Bone Histology Flashcards
What are osteoprogenitor cells
Mesenchymal origin with properties of stem cells; capacity to differentiate
Where are osteoprogenitor cells found?
Inner layer of periosteum and endosteum
What do osteoprogenitor cells give rise to?
Osteoblasts; they are deactivated during times of bone repair
What are osteoblasts?
They are epithelial like cells with cuboidal or columnar shapes; they deposit osteoid and control mineralization of osteoid; they give a strong cytochemistry reaction for alkaline phosphates
what are osteocytes?
Cells that come from osteoblasts that were trapped inside lacunae within the osteoid matrix they deposited
Where do osteoclasts come from?
Monocytes in bone marrow; become osteoclasts in bone matrix
What do osteoclasts do?
Generate a secluded acidic environment for bone restoration; important role in bone remodeling and renewal
What are the principle functions of periosteum and endosteum?
Nutrition of osseous tissue; continuous supply of new cells for growth and repair; periosteum does not cover articular surfaces of bone
What is in the inner layer of periosteum?
Osteoprogenitor cells and osteogenic layer
What is in the outer layer of periosteum?
Rich in blood vessels and nerves; fibroblasts and collagen fibers; sharpey’s fibers (anchoring collagen fibers penetrate the outer circumferential lamellae)
What does endosteum do?
Covers spongy walls
Extends into all cavities of bone
What is intramembraneous ossification? What are the steps?
Formation of bone (flat bones) by condensation of mesenchyme, deposition of osteoid tissue by osteoblasts on mesenchymal surface; entrapment of first osteocytes and formation of periosteum; creation of spongy bone; vascular channels are closed off to form distinct layer of bone
What are the steps of endochondral ossification
Mesenchyme develops into a body of hyaline cartilage covered with a fibrous perichondrium
Perichondrium stops producing chondrocytes and starts producing osteoblasts
Blood vessels penetrate the bony collar and invade the primary ossification center, this produces primary marrow cavity
Osteoblasts line the cavity, deposit osteoid and form the spongy bone
A wave of cartilage death progresses toward the ends of the bone and osteoclasts follow the wave enlarging the marrow cavity of the diaphysis prep
Chondrocytes enlargement and death create a secondary ossification center in the epiphysis
The epiphysis will fill with spongy bone and cartilage is limited to epiphyseal plate
What are the 5 steps of periosteal bone growth?
- An osteoblasts forms from a bone trabecular. Edges of the trabecula extend toward each other
- The ridges fuse and the groove changes into a body tunnel enclosing the blood vessel
- Additional bone lamellae are deposited around the tunnel which is then converted to Haversian canal containing a blood vessel
- The haversian vessel continue to receive blood through the canals of Volkmann extending obliquely across the diaphysis
- When the bone reaches full size, outer and inner circumferential lamellae provide the boundaries of the compact bone consisting of multiple osteoblasts
What are the four steps of bone fracture repair
- Formation of fracture hematoma
- Fibrocartilaginous callus formation (by chondroblasts)
- Bony callus formation (osteoblasts lay down osteoid)
- Bone remodeling (osteoclasts)
