Bone formation Flashcards
Mention the 4 components of bone
- Bone Cells
- Calcified Matrix
- Periosteum: the outer covering
- Endosteum: the inner layer facing the marrow cavity
Mention the types of bone cells
- Osteoprogenitor cells (Forming)
- Osteoblasts cells (Immature cells)
- Osteocytes (Mature cells)
- Osteoclasts
Osteoprogenitor cells arise from …………..
Mesenchymal stem cell
Osteoprogenitor cells differentiate into ……………..
Osteoblasts
Where are Osteoprogenitor cells found?
Periosteum and Endosteum
Outline the features of osteoblasts
- They are derived from osteoprogenitor cells and can divide.
- They have cytoplasmic processes which are extensions of the cytoplasm.
- Basophilic cells on the surface of the bone (in periosteum and endosteum)
- Protein secreting cells.
……………… secrete the organic part of the bone matrix
Osteoblasts
After the osteoblasts secrete the bone matrix, it becomes osteocyte in a small space called the …………………
Lacuna
What are osteocytes?
Osteocytes are mature bone cells with flattened nucleus and cytoplasmic processes.
They cannot divide.
Lacunae are connected together by small canals called ………..
Canaliculi
………………. contain the cytoplasmic processes of the osteocytes.
Canaliculi
…………………… connect the processes of the osteocytes in the canaliculi.
Gap junctions
Osteoclasts originate by ………………?
The fusion of cells in the bone marrow
What are osteoclasts?
Multinucleated, motile, and acidophilic cells in the endosteum.
Osteoclasts are, motile, and acidophilic cells in the ………….
Endosteum
Osteoclasts have cytoplasmic processes called ……………..
Ruffled border
How do osteoclasts maintain the Ca++ level in blood
They secret enzymes that digest and remove bone matrix forming cavities and canals to maintain the Ca++ level in blood
Bone matrix consists of two components, namely:
Organic components
Inorganic components
What are the inorganic components of the bone matrix
Calcium & phosphorus forming hydroxyapatite crystals.
Name the organic components of bone matrix
- Type 1 collagen
- Chondroitin sulfate.
In H&E section, is the decalcified bone matrix acidophilic or basophilic?
Acidophilic
The bundles of collagen in the matrix form parallel layers called …………………
Bone lamellae
What is the outer covering of a bone?
Periosteum
What is the outer covering of a bone?
Periosteum
What are the functions of the periosteum?
Bone formation and repair
Mention the two layers of the periosteum
- outer fibrous layer of dense connective tissue attached to a bone by collagen fibers.
-inner cellular layer (Osteogenic layer) of osteoblasts and osteoprogenitor cells.
What are the two forms in which bones exist in?
Compact bone which forms the outer part of all bones in the body.
Cancellous (spongy) bone
Describe the cancellous (spongy) bone form
Cancellous (spongy) bone forms the inner part of all bones and is more in the epiphysis (the ends of a long bone) than in the diaphysis (the shaft of a long bone).
………………. forms the outer part of all bones in the body.
Compact bone
Outline the features of the compact bone.
- The matrix of a compact bone consists of regular lamellae of calcified type 1 collagen.
- The lamellae form parallel cylinders called osteons or haversion systems.
- Osteons are found deeply in the compact bone.
In summary, each osteon consists of lamellae, which are layers of compact matrix that surround a central canal called the Haversian canal
The concentric lamellae forming the osteons are called ……………..
Osteonal lamellae
Under the periosteum and endosteum, the lamellae do not form osteons and are called ……………….
Circumferential lamellae
Outline the canals in compact bone
Harversian canal in the centre of each osteon contains osteoblasts, osteoclasts, and blood vessels.
Volkman’s canals contain blood vessels and connect the harversion canals of adjacent osteons.
Canaliculi connect the lacunae with Haversion canals for nutrition of the osteocytes.
……………… connect the lacunae with Haversion canals for nutrition of the osteocytes.
Canaliculi
…………….. canals contain blood vessels and connect the harversion canals of adjacent osteons.
Volkman’s
……………. canal in the centre of each osteon contains osteoblasts, osteoclasts, and blood vessels.
Harversian
Do the lamellae of spongy bones form osteons?
No
The lamellae of spongy bone do not form osteons, but they form ………………………..
Interconnected trabeculae
What is the function of canaliculi in trabeculae?
In Trabeculae, the canaliculi connect lacunae to bone marrow for nutrition of osteocytes.
What are the two methods through which bone is formed?
Intamembranous ossification
Endochondral ossification —intracartilagenous ossification
How does endochondral ossification occur?
Hyaline Cartilage is formed first and then replaced by bone. The long bones are an example
The trabeculae in cancellous bones are separated by ………………
bone marrow spaces lined by endosteum
Define intermembranous ossification
In this type of ossification, bone is formed directly in a membrane of mesenchymal cells without the formation of cartilage, as in Flat bones of the skull
State the order of bone formation from mesenchymal cells
- Mesenchymal cells differentiate into osteoprogenitor cells and osteoblasts.
- Osteoblasts secrete bone matrix and form the periosteum.
- Osteoblasts, lining the surface of bone, secrete collagen and the organic matrix of bone (osteoid), which becomes calcified soon after it has been deposited. As they become trapped in the organic matrix, they become osteocytes.
- Calcium salts are deposited in the matrix to form bone.
……………… remove part of the bone to form marrow spaces
Osteoclasts
Outline the steps of endochondral ossification
- Mesenchymal cells first form Hyaline cartilage.
- Blood vessels enter perichondrium which becomes periosteum and secretes bone collar on surface of cartilage.
- Cartilage in centre degenerates leaving cavities.
- Blood vessels and osteoblasts from periosteum enter the cavities to form the primary ossification centre in the diaphysis.
- Osteoblasts secrete bone matrix.
- Osteoblasts mature into OSTEOCYTES
OSTEOCLASTS in the ossification centre remove part of the new bone to form the bone marrow cavity.
After ossification, a piece of cartilage called ………………….. remains between the epiphysis and diaphysis.
Epiphyseal growth plate
Mention the 6 zones of ossification of epiphyseal plate
- Zone of cartilage reserve (resting).
- Zone of proliferation of chondrocytes.
- Zone of hypertrophy of chondrocytes.
- Zone of calcification of cartilage.
- Zone of ossification (formation of bone on the calcified cartilage matrix).
- Zone of resorption by osteoclasts.
Spongy bone is replaced every ……….. years
3-4 years
What is bone remodelling?
A balance between osteoblast formation and osteoclast degredation
Compact bone is replaced every ………… years
10
State the sequence of bone remodelling
Remodling is usually initiated through osteoclast activation and removal of the bone matrix
This is followed by osteoblast production of new bone
State the process of bone remodelling after fractures
-Blood clot will form around break
- Fracture hematoma follows
- Inflammatory process begins
- blood capillaries grow into clot
- phagocytes and osteoclasts
- Damaged tissues are removed
-Procallus forms and is invaded by osteoprogenitor cells and fibroblasts
- Collagen and fibrocartilage turns procallus to fibrocartilaginous (soft) callus
- Broken ends of bone are bridged by callus
- Osteoprogenitor cells are replaced by osteoblasts and form spongy bone
- Bony (hard) callus is formed
- Callus is resorbed by osteoclasts and compact bone replaces spongy bone.
