Bone Structure & Histology Flashcards
(23 cards)
Three types of collagen?
Elastin, hyaline and fibrocartilage
Features of hyaline cartilage
Articular cartilage, most common type
Avascular
Slippery, smooth and resistent to compression
ECM = Type 11 collage, 70% water, GAGs, hyaluronic acid, , proteins (i.e. chondroitin sulphate)
Chondrocytes maintain cartilage
What is the structure of the bone cortex?
Strong, outer part of bone
Made up of compact bone covered externally by periosteum and internally by endosteum
What is the structure of compact bone?
Made up of bony columns running longitudinally (along stress lines) = Haversian Systems
Lined externally by periosteum and internally by endosteum
What are Haversian Systems (Osteons)?
Bony columns only in compact bone Concentric lamellae (layers) of bone with a central canal (Haversian canal) that contains the neuromuscular bundle
Neurovascular bundles and periosteum and endosteum are interconnect via Volkman’s canals
What are the features of periosteum and endosteum?
Periosteum = fibrous & vascular supply
Contains fibroblasts, fibrous tissue, vessels, some osteoprogenitor cells
Endosteum = cellular
Contains many osteoprogenitr cells
What structures allow strong grip of tendons at bone?
Sharpey’s fibres
Collagen of the tendons become continuous with the compact bone and fibres penetrate the bone for strong attachment
What is the structure of the medullary cavity?
Hollow inside of bone
Contains interconnected struts of trabecular bone (cancellous) with fat (marrow) and vessels between
What are the features of trabecular bone?
‘Spongey bone’
Don’t contain aversion systems
Attach to the internal layer of the compact bone and project as struts that are interconnected
Have a thin lining of endosteum
Less structured and ordered than compact bone
What is the difference between red and yellow marrow?
Red marrow is haematopoietic and is found in the long bones early on but is replaced by yellow marrow in most bones with age (except flat bones, such as pelvis, skull, spinal cord)
Yellow marrow is largely fat with no haematopoietic function but can be reactivated to red marrow later in life if required
What is the arrangement of blood supply to the bone?
Vessels enter the marrow and run ‘north and south’ to supply medullary cavity. There are vessels that perforate the bone to supply the outer compact bone
Periosteum has its own supply, as does the diaphysis and epiphysis
What are the features & function of osteoprogenitor cells?
Mesenchymal origin
Give rise to osteoblasts
Found in the periosteum and endosteum (mainly endosteum)
Flattened cells that are difficult to see
Activated by damage to the bone
What are the features & function of osteoblasts?
Arise from osteoprogenitor cells
Create new bone - lay down osteoid
Osteoid = growth factors, cytokines, ECM (collage Type 1 + proteins)
Add new layers to the bone surface (outside)
They can become quiescent but become large & plump when active
Similar to plasma cells - can see ribosomes & paranuclear hoff
What are the features & functions of osteocytes?
Osteocytes arise from osteoblasts that become entombed by bone while laying down new osteoid
The space that surrounds them = lacunae
They are important in maintaining the health of the bone matrix and for mineralisation of the bone (breakdown local bone to liberate Ca for hydroxyapetite)
Receive nutrition from small cytoplasmic extensions to the endosteum = canaliculae
What are the features & functions of osteoclasts?
Arise from a monocyte lineage
Destroy bone in normal remodelling, growth and repair
Large cells with multiple nuclei
Secrete H+, Cl-, proteases to destroy ECM
Maturation and thus activity is influenced by osteoblasts, PTH and oestrogen
What process leads to osteoclast maturation and activity?
What influences this interaction?
Osteoblasts contain RANK receptor which interacts with the RANKL (ligand) on immature osteoblasts
When binding occurs osteoblasts mature and increase in activity
OPG produced by osteoblasts circulates and can bind to RANKL to prevent it binding to RANK
Oestrogen reduces OPG and increases RANK/RANKL - decreases maturation and activity
PTH increases maturation & activity by increasing RANKL
What two processes form bone in development?
Which is more common?
Which bones result from which process?
Endochondral ossification and membraneous bone formation
Endochondral more common
Endochondral = long bones, appendicular skeleton, weight bearing bones Membranous = skull, clavical and flat bones of face & jae
What is the process of endochondral bone formation?
- Start with cartilage model
- Perichondrium becomes periosteum, forming a bone collar around the diaphysis
- Primary centre of ossification in centre of diaphysis cavity
- Invasion of shaft by osteoprogenitor cells, mesynchmal cells and blood vessels
- Cartilage replaced by bone at the at the growth plate forming a perforated trabecular matrix
- Elongation of the diaphysis occurs as growth plates move away from each other
- Secondary ossification centres develop in each of the epiphysis of the bone - same process of new bone formation
What are the features & layers of the growth plate?
Growth plate (epiphyseal plate) is the interface between the diaphysis and epiphysis = cartilage + bone (metaphysis)
Contains layers of chondrocytes at different stages & a layer of new bone - new bone added from the diaphysis side of the growth plate
At the epiphysis side (distal) to the proximal side:
- Resting zone - resting chondrocytes
- Proliferative zone - proliferating chrondrocytes to maintain the growth plate
- Maturation zone - mature chondrocytes
- Hypertrophic zone - dying chrondrocytes (‘smothered’ by new bone layer)
- Ossfication zone - dying chrondrocytes replaced with osteoid
What is membranous bone formation?
Myesenchymal cells differentiate into osteoprogenitor cells, which develop into osteoblasts
Osteoblasts deposit osteoid directly into the embryological tissue to form new bone
What type of bone is first layed down during bone production in development?
What other situations is it also produced?
Woven bone
Produced by endochondral ossification and also during bone repair and in some pathological processes
What are some features of woven bone?
It is temporary - is remodelled to lamellar bone
It is weaker, has more cells and collagen and no haversian systems than lamaellar bone
How is woven bone remodelled?
Woven bone is remodelled by osteoblast and osteoclast activity
In compact bone remodelling produces Haversian systems (osteons)
- Osteoclasts tunnel cavities in the bone longitudinally along axis of stress, bringing endosteum and vessels with it
- Osteoblasts from endosteum lay down osteoid in concentric layers with collagen of each layer running in opposite directions
- Last concentric layer leaves a space forming the aversion canal where neuromuscular structures run
