Bone Flashcards
Where does endochondral ossifcation occur?
Axial skeleton, appendicular skeleton and base of skull
Does endochondral ossification involve a cartilaginous model first made by chondrocytes?
Yes, it is later replaced with woven bone and then remodelled to lamellar bone
When do adults have production of woven bone?
After fractures and in Pagets disease
What is achondroplasia?
Achondroplasia is a disorder of bone growth that prevents the changing of cartilage (particularly in the long bones of the arms and legs) to bone. It is characterized by dwarfism, limited range of motion at the elbows, large head size (macrocephaly), small fingers, and normal intelligence.
Where does membranous ossification occur?
The calvarium, facial bones and clavicle
Does membranous ossification involve a cartilage template?
No, woven bone is formed directly and later remodelled to lamellar bone
Which molecules can be measured to indicate osteoblast activity?
ALP, osteocalcin, propeptides of type I procollagen
What do osteoclasts secrete?
H and collagenases
How are osteoclasts regulated?
Osteoblasts secrete RANKL which binds the RANK receptor on osteoclasts and activates them. However osteoblasts also have OPG which is a RANKL decoy.
What effect does parathyroid hormone have at low intermittentt levels?
Anabolic effects — building bone
What effect does parathyroid hormone have at chronically increased levels?
Catabolic effects -> osteitis fibrosa cystica
How does estrogen effect bone formation?
Inhibits apoptosis in osteoblasts and increases apoptosis in osteoclasts. Causes closure of epiphyseal plates during puberty
What is osteoid composed of?
Type I collagen and hydroxapatite
