Histology of cartilage, bones and joints Flashcards
What does the ECM of hyaline cartilage consist of?
Collagen type II
Aggrecans (large GAGs)
Hyaluronic acid
Chondronectin (glycoprotein)
Which is the most common type of cartilage?
Hyaline cartilage
Which cell type maintains cartilage?
Chondrocytes
How does elastic cartilage differ from hyaline cartilage?
Also contains elastin
Describe the properties of elastic cartilage?
Flexible
Maintains shape
Describe the structure of fibrocartliage?
Dense connective tissue
Isolated strands of cartilage
Where are each of the three types of cartilage found?
Hyaline cartilage: ribs, trachea, joints
Elastic cartilage: ear, ear canals, epiglottis, larynx
Fibrocartilage: menisci, IV discs
Describe the structure of compact bone?
Outermost: concentric layers
Rest as Haversian systems
Describe the structure of trabecular bone?
Lamellae
Continuous spaces filled with marrow and blood vessels
Where do ostecosyctes lie within the bone?
Between trabeculae
Describe the contents of the medullary cavity?
Bone marrow: red or yellow
Blood vessles include sinusoids instead of capillaries
Describe the difference between red and yellow marrow?
Red marrow early in life, yellow later
Red marrow mainly haematopoietic cells
Yellow marrow preserves some haematopoietic cells and can become active if needed
What is the periosteum?
Where is it found?
Thin layer of connective tissue
Covers inner and outer surface of bone
Not where tendon or ligament anchors to bone
Outer fibrous layer (fibroblasts, BVs, collagen)
Inner cellular layer (osteoprogenitor cells)
What is the endosteum?
Where is it found?
Thin layer of connective tissue
Covers bone lining inner marrow cavity
Not found where a tendon or ligament anchors to bone
What are Sharpey’s fibres?
Collagen fibres penetrating bone surface
Where tendons and ligaments attach to bone
Bone collagen continuous with collagen of ligament or tendon
Describe the blood and nerve supply to bone?
Branch in marrow cavity
Shaft and ends supplied separately
Periosteum supplied separately
Nerves follow vessels
Describe articular cartilage?
Hyaline cartilage
Slippery, smooth, resistant to compression
No perichondrium
Describe the contents of the synovial space?
Synovial fluid
Lined by synovial membrane
Describe the structure of the synovial membrane?
Surface layer (intima): 2-3 cells thick, contains fibroblast-like and macrophage-like cells
Sub-intimal layer: fibrous connective tissue
Not an epithelium!
Describe why the synovial membrane is not an epithelium?
Lacks basement membrane, tight junctions and desmosomes
Very leaky
Why is the synovial membrane so leaky?
Allos synovial fluid to easily enter joint space
What are Haversian systems?
Where are they found?
Long, branched, cylindrical columns of bone surrounding a central blood vessel
Found in dense bone
Which cells are present in bone?
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
Where are osteoprogenitor cells found?
Periosteum and endosteum
Describe the appearance of osteoprogenitor cells?
Flattened
Describe the purpose of osteoprogenitor cells?
Usually quiescent
Can give rise to new osteoblasts
Describe the appearance of inactive osteoblasts?
Flattened - like osteoprogenitor cells
Describe the function of osteoblasts?
Make osteoid to make bone
Where are osteocytes found?
Surrounded by bone
Describe the function of osteocytes?
Maintain immediate environment around them
Maintain bone in response to loading
Capable of destroying local bone to free calcium
Describe the appearance of osteoclasts?
Giant multinuclear cells
Describe the function of osteoclasts?
Seal to bone around edge
Secrete H, CL and proteases to resorb bone
Where are osteoclasts derived from?
Bone marrow
Related to granulocytes/macrophages
Describe the type of bone that is laid down during development?
During development, bone is laid down as membrane bone or endochondral bone
Membrane bone: from mesenchyme; skull and flat bones of face, mandibe and clavile
Endochondral bone: weight bearing bones and bones of extremities
Describe endochondral bone formation?
Cartilage model of bone produced > cartilage destroyed > replaced by bone
Describe the process of replacing cartilage with bone?
Bone collar forms around diaphysis > cartilage beneath collar degenerates > blood vessles invade > bone cell progenitors arrive > second nucleus of ossification appears at each epiphysis > zones of ossification grow, leave behind growth plate
What is the grwoth plate?
Thin zone of cartilage
Enables long bones to grow
Describe the structure of the growth plate?
DISTAL TO PROXIMAL
Normal hyaline cartilage (resting zone)
Dividing chondrocytes (proliferation zone)
Mature chondrocytes (maturation zone)
Hypertrophic/dying chondrocytes (hypertrophic zone)
Ossification
What is woven bone?
Describe its structure?
New bone that appears during development or repair
More cellular, more collagen, no Haversian systems
Soon remodelled
Describe the process of remodelling bone?
Osteoclasts form cavities in bone, that are the size and shape of Haversian systems and appear along the stress axis of bone
Blood vessels and endosteum invade
Osteoblasts lay layers of bone with collagen alternating in direction
Final layer leaves narrow space around blood vessel (Haversian canal)
What is a Haversian canal?
Narrow space between final layer of bone and blood vessel in a Haversian system
