Bone Flashcards
What happens during the haematoma stage of fracture repair?
Blood vessels in the bone and periosteum break.
A mass of clotted blood (haematoma) forms.
Bone cells at the fracture edge die (no blood supply).
Swelling and inflammation occur.
Phagocytic cells and osteoclasts begin to remove dead and damaged tissue.
Macrophages will eventually remove the blood clot.
What happens during fibrocartilaginous callus formation?
New blood vessels infiltrate the fracture haematoma. A procallus (soft callus) of granulation tissue (i.e. Tissue rich in capillaries and fibroblasts) develop. Fibroblasts produce collagen fibres that span the break. Others differentiate into chondroblasts that give rise to a sleeve of hyaline cartilage. An externally bulging, fibrocartilaginous matrix thus splits the broken bone. Osteoblasts from the nearby periosteum and endosteum invade the fracture site and begin bone reconstruction by forming spongy/trabecular bone.
What happens at bony callus formation?
Trabeculae develop as the former fibrocartilagenous callus is converted to a hard callus of cancellous bone.
Endochondral ossification replaces all cartilage with cancellous bone, but also intramembranous ossification also produces new cancellous bone in the area.
(Bony callus formation continues for approx 2 months until a firm union is formed)
What happens at bone remodelling?
As soon as it is formed, the callus of spongy bone begins to be remodelled into compact bone, especially in the cortical region.
This process continues for several month
The material bulging from the outside of the bone is removed by osteoclasts- refined.
The final shape of the remodelled area is the same as that of the unbroken bone because it responds to the same set of mechanical stressors - WOLFES LAW
What are the differences between autograft, homograft and heterograft?
Autograft - donor is the recipient (most successful)
Homograft - donor is a different human (may be rejected as foreign)
Heterograft - donor is a different species (least successful)
What is osteoporosis?
Enhanced bone reabsorption relative to formation.
What does the endosteum do?
It is the boundary between the cortical bone and cancellous bone.
What is cortical bone covered with?
A periosteum.
What are osteoblasts and osteocytes derived from?
Osteoprogenitor cells
What are osteoclasts derived from?
The same cells that differentiate to form macrophages and monocytes.
What are osteoblasts? Where are they found?
They are mononucleate bone forming cells.
They are found on the surface of osteon seams and make a protein mixture called an osteoid- this mineralises to become bone.
What is osteoid primarily composed of?
Type 1 collagen.
What are osteocytes?
Osteocytes are mostly inactive osteoblasts.
Osteocytes originate from osteoblasts that have migrated into and become trapped and surrounded by the bone matrix they themselves produced. The spaces they occupy are known as lacunae.
How do osteocytes communicate?
Osteocytes have slender cytoplasmic processes which reach out to those of adjacent osteocytes via caniculi.
These processes connect via GAP JUNCTIONS so nutrients can pass between osteocytes.
(Caniculi are also believed to be connected with the central Haversian canal)
What are osteoclasts? Do they have one nuclei?
Cells responsible for bone resorption.
Osteoclasts are large cells with MULTIPLE NUCLEI located on the bone’s surface located in Howship’s lacunae (or resorption pits).
