Bones Flashcards
- Red bone marrow function
2. What eventually happens to it?
- Red marrow is important in the synthesis of blood cells
2. Converts to yellow marrow with maturation
- Bone without mineral would be___
2. Bone without collagen would be __
- Flexible
2. Brittle
Macrostructure of bones:
- What are the two types
- Where is each found?
- Compact and trabecular (spongy/cancellous)
2. Compact = diaphysis (shaft) of long bones; spongy= epiphysis of long bones and in short and irregular bones
- How is compact bone formed?
- Where is the vasculature transmitted?
- What are canals surrounded by?
- Where are osteocytes confined to in bone?
- Densely packed ostensibly
- Central (haversian) canals
- Concentric deposits of bone matrix and osteocytes called lamellae
- Lacunae (which are spaces in lamellae)
- Trabecular bone is formed by?
2. Contained within?
- More diffuse ostensibly
2. Bone marrow
Function of periosteum?
Briefly describe its two layers
Endosteum?
Lines the outer surface of bone
Outer layer- fibrous tissue continuous with attaching muscle tendons and collagen of the bone
Inner layer- osteogenic cells that can differentiate into osteoblasts
Endosteum lines inner surface of the bone; thin (often 1 cell) layer of osteogenic and bone lining cells
Why do the fibers change direction in each successive lamella?
Makes it more pliable in strength (form right angles to each other)
New osteons can form in mature, compact bone by internal remodeling. What happens?
Osteoclasts cut a path and then osteoblasts secrete new lamellae
4 types of bone cells and their function
- Osteogenic cells - stem cells in the periosteum and endosteum that give rise to osteoblasts
- Osteoblasts - form bone tissue; when entombed in the matrix, they become osteocytes
- Osteocytes - maintain bone tissue; matrix will be resorted without osteocytes
- Osteoclasts - resorb bone tissue (break it down)
What role does filopodia have with osteocytes?
Filopodia travel in canaliculi and allow osteocytes to communicate across gap junctions
(Canaliculi are little tunnels)
What are the two forms of bone growth?
Main function of each?
Main difference?
Intramembranous and endochondral
Intramembranous - contributes to growth of short bones and thickening of long bones
Endochondral - source of most weight bearing bones
In intramembranous, bone develops directly from sheets of mesenchymal connective tissue; in endochondral, bone develops by replacing hyaline cartilage
Broad mechanism of intramembranous ossification
Bone formation begins at ossification centers, osteoblasts secrete osteoid and then osteoblasts transform to osteocytes as they are surrounded by calcified bone matrix, osteoclasts break down the calcified bone to form trabeculae (harbors red marrow), ossification centers fuse (regions with more deposition than absorption will be compact bone), periosteum forms on surface of osteoblast layer
Main takeaways from endochondral ossification?
Bone grows within a preformed cartilaginous mold, model lengthens and widens and blood vessels invade, primary ossification zone replaces zone of calcified cartilage (because calcification kills chondrocytes), secondary ossification center forms around epiphyseal vessels around time of birth
- Epiphyseal line represents?
2. Articular cartilage represents?
- Point where primary and secondary ossification centers join
- Remnant of hyaline cartilage model
Endochondral ossification - bone grown after early development occurs at epiphysial plate - 5 zones?
Resting zone- reserve cartilage
proliferative zone- columns of chondrocytes that produce cartilage matrix lengthening the bone
hypertrophic cartilage zone- large chondrocytes that produce thin septa
calcified cartilage zone- septa calcifies,
chondrocytes die
Zone of resorption - osteoblasts secrete bone matrix over calcified cartilage spicules (epiphyseal line ossifies ~20 years old)
