Ultrastructure of Bone Flashcards
list the numerous functions of bone
- Haematopoiesis
- Lipid and mineral storage – bone is a reservoir holding adipose tissue within the bone marrow and calcium within the hydroxyapatite crystals.
- Support
- Protection
what is haematopoiesis?
– the formation of blood cells from haematopoietic stem cells found in the bone marrow.
what are the three cellular components of bone?
osteoblasts
osteocytes
osteoclasts
describe the function of osteoblasts
Synthesise uncalcified/unmineralised extracellular matrix called osteoid. This will later become calcified/mineralised to form bone.
describe the function of osteocytes
As the osteoid mineralises, the osteoblasts become entombed between lamellae in lacunae where they mature into osteocytes. They then monitor the minerals and proteins to regulate bone mass.
describe the function of osteoclasts
Derived from monocytes and resorb bone by releasing H+ ions and lysosomal enzymes. They are large and multinucleated cells.
describe the extracellular matrix (ECM)
The ECM of bone is highly specialised. In addition to collagen and the associated proteins usually found in connective tissue, bone is impregnated with mineral salts, in particular calcium hydroxyapatite crystals. These crystals associate with the collagen fibres, making bone hard and strong. This matrix is organised into numerous thin layers, known as lamellae.
what is the external connective tissue layer found on bones called?
periosteum
which connective tissue layer lines the cavities of bone?
endosteum
describe compact bone
Compact bone forms the outer ‘shell’ of bone. In this type of bone, the lamellae are organised into concentric circles, which surround a vertical Haversian canal (which transmits small neurovascular and lymphatic vessels). This entire structure is called an osteon and is the functional unit of bone.
where are osteocytes located in compact bone?
Osteocytes are located between the lamellae, within small cavities (known as lacunae). The lacunae are interconnected by a series of interconnecting tunnels, called canaliculi.
describe spongy bone
Spongy bone makes up the interior of most bones and is located deep to the compact bone. It contains many large spaces – this gives it a honeycombed appearance.
The bony matrix consists of a 3D network of fine columns, which crosslink to form irregular trabeculae.
The spaces between trabeculae are often filled with bone marrow.
what is yellow bone marrow composed of?
adipocytes
what is red bone marrow composed of?
haematopoietic stem cells
what is red bone marrow composed of?
haematopoietic stem cells
what is ossification?
Ossification is the process of producing new bone. It occurs via one of two mechanisms:
Endochondral ossification.
Intramembranous ossification
what is endochondral ossification? and give an example of a bone that undergoes this
– Where hyaline cartilage is replaced by osteoblasts secreting osteoid. The femur is an example of a bone that undergoes endochondral ossification.
what is intramembranous ossification? give an example of bones that undergo this
– Where mesenchymal (embryonic) tissue is condensed into bone. This type of ossification forms flat bones such as the temporal bone and the scapula.
describe bone remodelling
This is the process whereby mature bone tissue is reabsorbed, and new bone tissue is formed. It is carried out by the cellular component of bone.
Osteoclasts break down bone via a cutting cone. The nutrients are reabsorbed, and osteoblasts lay down new osteoid. Remodelling occurs primarily at sites of stress and damage, strengthening the areas affected.
What is interstitial bone growth?
In interstitial growth, chondrocytes secrete new matrix within the cartilage and this causes it to grow in length. eg. epiphyseal plate of femur
what is appositional bone growth?
Appositional growth occurs when chondroblasts secrete new matrix along existing surfaces and this causes the cartilage to expand and widen.
