PW - Structure and function of the components of bone

Question 1

What are the 4 key cell types in bone?

Answer 1

• osteoprogenitor cells/mesenchymal stem cells
• osteoblasts
• osteocytes
• osteoclasts

Question 2

What are the four key cell types in bone and then describe their functions in bone growth… (def an exam question)

Answer 2

OSTEOPROGENITOR CELLS/MESENCHYMAL STEM CELLS:
- resting cells that transform into osteoblast AND can also differentiate into chondroblasts, fibroblasts & adipose cells
- initiates intramembraneous ossification
- found on internal & external surfaces of bone
- periosteal & endosteal surfaces
- flattened, elongated cells with oval nucleus
OSTEOBLASTS:
- secrete the matrix of bone
- Cover bone everywhere except over articular
cartilage
- Inactive - similar to fibroblasts
- Active - cuboidal to columnar in shape with nucleus away from surface
- Basophilic cytoplasm rich in rER and ribosomes
- Cytoplasmic processes communicate with other osteoblasts and osteocytes by gap junctions
OSTEOCLASTS
 Responsible for removing bone
 Derived from blood monocytes
 Large multinucleate cells
 Located on surface of bone being removed  Form shallow depressions called Howship’s
lacunae
 Surface adjacent to bone infoldings of plasma membrane form “ruffled border”
 Canals between folds take enzymes from lysosomes to bone
OSTEOCYTES
 Mature cells of bone
 Enclosed by matrix which they maintain
 Located in lacunae
 Cytoplasmic processes in canaliculi communicate with neighbouring cells by gap junctions
 Less rER and more lysosomes than osteoblasts
 Osteocytic osteolysis