Bones 1,2,3. Flashcards
Name 4 basic functions of bone.
Weight bearing/support
Protection
Mineral store
Blood formation
Describe the basic anatomy of bones.
There is compact (cortical) and spongy (trabecular) bone.
In bones there are; blood vessels; bone marrow; membranes - periosteum and endosteum.
Describe the microstructure of compact bone.
Compact bone is organised in osteons or haversian systems.
Within the structure you will find, central haversian canal and horizontal Volkmann’s canals. Both of these canals contain blood vessels.
Around these haversian canals you find osteocytes and concentric rings of bone matrix (lamellae).
**canaliculi is where the ‘tentacles’ that connect osteocytes overlap.
Describe the structure of spongy (trabecular) bone.
Also called cancellous or trabecular bone or diploe.
Less dense than compact bone.
No haversian systems.
The orientation of trabeculae reflect main directions of mechanical forces.
In living bone, the network of lamellated trabeculae is filled with bone marrow.
Describe the development of bone as the result of endochondral ossification.
The word endochondral means inside cartilage.
This process of bone development involves a cartilage model of bone being formed first.
Blood vessels then invade the cartilage, and the cartilage is replaced with bone. The cartilage remains in the epiphyseal growth plate. The growth plate eventually ossifies.
Describe the development of bone as a result of intramembranous ossification.
Mesenchymal stem cells develop into osteoprogenitor cells that mature into osteoblasts that start depositing bone.
Residual mesenchymal cells develop blood vessels and bone marrow.
This bone formation also occurs in adult bone.
Describe the composition of bone. (cells and ec matrix)
Bones are made up of cells; osteoclasts, osteoblasts; osteocytes.
They are made up of an extracellular matrix, which is made of 45% hydroxyapatite crystals (complex form of calcium phosphate), 35% collagen type 1, and 20% water.
They are strongly cross-linked, and there are large ‘gaps’ within fibres.
The gaps provide space for hydroxyapatite crystals. The orientation of the collagen fibres is linked to the mechanical forces.
Describe bone as a composite material, and the structure - function relationship.
Minerals (hydroxyapatite) make bones stiff and able to support structure - they have a high strength under compression.
Collagen gives bone some flexibility and reduce risk of fracture - have a high strength under tension.
Bone is a very dynamic tissue, useful for fracture healing and mechanical adaptation.
Describe the process of bone turnover/remodelling.
This is a constant process where bone is continuously renewed.
Osteoclasts break down the old bone, and osteoblasts build the new bone.
Healthy bone has a balance between bone removal and formation.
Describe osteoclasts.
Osteoclasts are large multinucleate cells derived from haemopoietic stem cells (like macrophages).
Found on bone surface, they resorb bone matrix. “Ruffled border” releases acid to dissolve bone matrix.
We call the resorption pits, “Howships’ lacunae”
Describe osteoblasts.
Immature bone cells created from osteoprogenitor cells in periosteum and endosteum.
(the osteoprogenitor cells developed from mesenchymal stem cells.)
*they produce bone matrix (unmineralized matrix = osteoid) and initiate calcification.
Define osteocytes.
Osteocytes are mature bone cells found inside lacunae.
Numerous processes lying in canaliculi.
Canaliculi connect lacunae to each other - allows communication between cells.
The function of osteocytes is not well understood, may maintain bone matrix and sense mechanical forces.
Describe bone marrow (yellow and red) and its function.
Red bone marrow resides in the cavities of some bones in the body, long bones contain the most red bone marrow. Red bone marrow is the primary site where haemopoiesis occurs. In infants and young children, all bones in the body contain red bone marrow. However as we age, some red bone marrow changes to yellow bone marrow in some bones, and yellow bone marrow is used for fat storage.
