MSK histology Flashcards
What are the primary functions of bone in the body?
- Support <br></br> - Levers for effective movement <br></br> - Protection of internal organs <br></br> - Calcium storage <br></br> - Haemopoiesis (blood cell production)
Where is more than 95% of the total calcium found in the body?
It is found in bones, and there is a constant exchange of calcium between bone and the blood.
How does intramembranous ossification differ from endochondral ossification?
- Intramembranous ossification occurs from fibrous membranes, forming flat bones of the skull, mandible, and clavicles. <br></br> - Endochondral ossification occurs from hyaline cartilage, forming most bones in the body.
Which bones are primarily formed through intramembranous ossification?
Flat bones of the skull, mandible, and clavicles.
Where does endochondral ossification take place in bone development?
It occurs in the rest of the body’s bones. Cartilaginous bones initially ossify within the diaphysis and secondarily within the epiphysis.
How is bone girth increased?
By cells from the periostrum laying down circumferential new bone on the periphery of the existing cortex.
How is bone length increased?
Through cartilage proliferation at growth plates between the metaphysis and epiphysis, followed by ossification of the cartilage.
When does blood cell production predominantly shift to bone marrow?
Blood cell production begins in the bone marrow well before birth and becomes the primary site of haemopoiesis by the time of birth.
At what age does blood production typically involve only the axial and limb girdle skeleton?
By the early 20s, typically only the axial and limb girdle skeleton is involved in blood production.
What are the components of bone composition?
- 65% bioapatite (a form of calcium phosphate, mostly hydroxyapatite) <br></br> - 23% collagen <br></br> - 10% water <br></br> - 2% non-collagen proteins
What is the function of the periosteum?
It covers the outer surface of all bones, except at the articular surfaces. It has an outer fibrous layer and an inner ‘osteogenic’ layer containing progenitor cells that develop into osteoblasts.
What makes up the outer shell of the bone shaft (diaphysis)?
Dense cortical bone.
What occupies the ends of the bone (epiphysis)?
Cancellous or trabecular bone.
What is the structural difference between compact and trabecular bone?
The main difference lies in the presence of spaces (marrow cavities) adjacent to trabecular bone. Both types are lamellar, made up of layers.
What is the functional unit of bone and its structure?
The osteon, consisting of concentric circles of lamellae surrounding a Haversian canal that transmits small vessels. Osteocytes are found between the lamellae within lacunae, interconnected by canaliculi.
Where are osteocytes found in bone and how are they interconnected?
Osteocytes are located within lacunae between the lamellae. They are interconnected by a series of interconnecting tunnels called canaliculi.
How does the microarchitecture of bone change with age?
At 20 years: strong, healthy bone. At 50 years: a decrease in trabecular thickness, especially for non-load-bearing horizontal trabeculae. At 80 years: a decrease in connections between vertical trabeculae and a decrease in trabecular strength.
What are osteoprogenitor cells and where are they located?
They are reserve osteoblasts located on bone surfaces, such as under the periosteum.
What is the function of osteoblasts and their origin?
Osteoblasts are bone-forming cells derived from mesenchymal cells in the bone marrow stroma. They have abundant RER (rough endoplasmic reticulum) and prominent mitochondria.
What characterizes osteocytes and their role?
Osteocytes are the primary cells of mature bone and are derived from osteoblasts that become buried in the bone matrix. They are believed to sense mechanical strain on the skeleton.
Describe osteoclasts and their origin.
Osteoclasts are large, multinucleated cells responsible for bone reabsorption. They are believed to be derived from the macrophage lineage of cells (haematopoietic progenitors), and several osteoclasts can fuse to form a giant cell.
What is bone remodeling, and what is the Basic Multicellular Unit (BMU)?
Bone undergoes a continuous remodeling cycle at distinct sites, involving osteoclasts drilling into the bone, followed by osteoblasts lining the tunnel and laying down new lamellar bone. The collection of osteoclasts and osteoblasts at a site is termed the BMU.
How does bone mineralization occur?
Osteoblasts secrete osteoid, a matrix of collagen, glycosaminoglycans, and proteoglycans that mineralizes over time in the extracellular space. The principal mineral of bone is calcium phosphate crystals, primarily hydroxyapatite.
What distinguishes woven bone from lamellar bone?
Woven bone is the first bone laid down during development or after a break, characterized by haphazardly oriented collagen fibers. It is weaker than lamellar bone and is remodeled into lamellar bone by osteoclasts breaking it down and new osteoblasts reforming it.
- Elastic cartilage: found in the auricle of the ear and most of the epiglottis.
- Fibrocartilage: found in intervertebral discs.
