BL 17 Flashcards
3 types of cartilage
- Hyaline cartilage
- Elastic cartilage
- Fibrocartilage
What does hyaline cartilage contain? (matrix and ground substance)
- Looks ‘glassy’
Matrix contains -
• type II collagen - laid down in a random pattern, no order
• hyaluronate proteoglycan aggregates bound to fine collagen matrix fibres (takes in lots of water)
• tough dense tissue often containing fluid
Ground substance -
All have matrix containing proteoglycan and hyaluronic acid
What does elastic cartilage contain? (matrix and ground substance)
Matrix contains:
- many elastic fibres and type II collagen in elastic lamellae (layers)
- tough but flexible tissue
What does fibrocartilage contain? (Matrix and ground substance)
Matrix contains:
• lots of type I collagen (mainly) - so is also the only cartilage which fibroblasts
• small amount of type II collagen fibres
Ground substance -
All have matrix containing proteoglycan and hyaluronic acid
Hyaline cartilage in more detail (cell type, role, the way the cells are present)
Cell type: chondrocyte (no other cell types are present).Chondrocytes are present as single cells or, if recently divided in small clusters called isogenous groups (isogenous groups - cluster of chondrocytes, all formed through division of a single progenitor cell, found in hyaline cartilage and elastic cartilage, growing by interstitial growth). The chondrocytes within the isogenous groups separate as they lay down extracellular matrix
note - bright blue is the cartilage being made
Role: In early fetal development - hyaline cartilage provides the precursor model for bones that develop by endochondral ossification. As long bones develop, hyaline cartilage remains at the articulating surface and at the epiphyseal plate until bone growth ceases.
Where? Articular ends of bones, parts of the rib cage, nose, and in the trachea, bronchi and larynx
How does hyaline cartilage form?
cartilage-forming cells, chondroblasts, begin to secrete the components of the extracellular matrix of cartilage. The extracellular matrix consists of, ground substance (hyaluronan, chondroitin sulfates and keratan sulfate) and tropocollagen, which polymerises extracellularly into fine collagen fibres.
Chondrocytes produce and maintain the extracellular matrix.
How does hyaline cartilage form?
Fibroblasts -> chrondroblasts -> chondrocytes
- Perichondral region: Contains elongated, fibroblast-like cells that develop into chondroblasts
- Maturing chondral region: Chondroblasts differentiating into chondrocytes. Chondroblasts are secreting the extracellular matrix.
- Mature chondral region: Chondrocytes sitting in lacuna. Chondrocytes are involved in the maintainance of the cartilage.
Difference between chondroblasts and chondrocytes
- Chondroblasts are an immature type of cells found in the cartilage.
- Chondroblasts are also known as perichondrial cells.
- Chondroblasts are a type of mesenchymal progenitor cells.
- They secrete the extracellular matrix of the cartilage.
- The extracellular matrix of the cartilage is composed of collagen, hyaluronic acid, glycoproteins, proteoglycans, and water.
- Chondroblasts can be found in the perichondrium of the cartilage.
Chondrocytes (more info, including pressure)
- Each chondrocyte lies in a lacuna
- There is artefactual shrinkage of the cells away from the lacunae walls in this preparation
- When placed under pressure, mechanical signals increase synthetic activity to release the pressure - Chondrocytes lay down extracellular matrix (blue in the image) within the cell as vesicles
- Fibres and GAGs/hyaluronic acid secreted into spaces between chondrocytes to cause tissue expansion
Hyaluronic acid in cartilage (role of this in hyaline cartilage)
- Similar to that in other connective tissues
- About 100 hyaluronate proteoglycan aggregates per collagen fibril
- Makes a very ‘stiff’ gel-like substance
- Attracts a lot of water - prevents compression
- Hyaluronic acid assists resilience to the repeated application of pressure
Where is hyaline cartilage found?
- Articular surface of bones
- Sternum, larnyx, tracheas, bronchioles, nose
Hyaline cartilage and H+E stain
Example 1 of hyaline cartilage - Tracheal wall
- Tube formed by C-shaped tracheal cartilages (HYALINE CARTILAGE)
- Cartilage in tube reinforces trachea and helps to protect and maintain the airway (makes sure the lumen stays open)
- Lined with pseudostratified ciliated epithelium
Example 2 of hyaline cartilage - Articular surfaces
What is rheumatoid arthiritis?
- Cartilage is broken down by enzymes or bacteria in the joint - hyaline cartilage doesn’t have the capacity to repair
- In the adult – cells do not proliferate enough to repair damage
- Fibroblasts lay down scar tissue instead
- Calcifies with age - Loss of flexibility
- Bony spurs (osteophytes) - fragments of cartilage in the joint can stimulate the bone to fill up the gaps = leads to osteophytes, the osteophytes are in the joint, this leads to joint pain
What happens when hyaline cartilage gets damaged?
- It does not have the capacity to repair
- Fibroblasts lay down scar tissue instead
Elastic cartilage (structure)
Cell type: chondrocyte (no other cell types are present)
Also contains elastic fibres – confers elasticity
Where is elastic cartilage found?
Only found in 3 places in the body:
• The pinna of the ear (and the external part of the acoustic meatus)
• the Eustachian tube
• the epiglottis
Elastic cartilage (where is the perichondrium, where is the cartilage)
- red = cartilage
- black line = perichondrium
- notice the chondrocytes are in lacuna
What does the elastic cartilage from the epiglottis look like?
What do fibroblasts make?
Type 1 collagen
What do chondrocytes make?
Type 2 collagen
Fibrocartilage structure (cells it contains, fibres etc) and role
- Cell types: Chondrocytes (make type 2 collagen) and fibroblasts (make type 1 collagen)
- Fibrocartilage is a combination of dense regular connective tissue and hyaline cartilage
- The cells are often seen distributed in rows
- There is no surrounding perichondrium (as already have fibroblasts in them)
• Role: The fibrocartilage acts as a shock absorber (to stop two bones banging together - as it has a high level of water) and to resist shearing forces and twisting actions
Fibrocartilage examples
What do fibrocartilage look like?
- Collagen fibres are stained green.
- The rounded chondrocytes tend to be arranged in rows, or as isogenous groups.
- There are a relatively small number of elongated fibroblast nuclei evident (see red arrows).
- Inset: high magnification of chondrocytes that have undergone mitotic division
What does fibrocartilage look like from meniscus of the knee?
- Very hap=hazard as the cartilage is moving in many directions (twisted, compressed etc)
Name the types of cartilage in the photo, point out 3 similarities between them all
Similarities:
• All contain chondrocytes (fibrocartilage also contains fibroblasts)
• All contain hyaluronic acid and proteoglycans
• Growth is by apposition
notice - lots of lacuna in elastic cartilage
What is the structure of a long bone like the femur? What does growth occur?
- Epiphyseal growth plates (this is where growth occurs, between epiphysis and diaphysis - it is made of hyaline cartilage)
- Diaphysis (long shaft)
- Metaphysis (end of the long shaft)
- Epiphysis (ends)
- Hyaline cartilage (articulated surfaces)
Describe the steps in endochondral ossification (from hyaline carilage to the formation of a bone collar)
Endochondral ossification (from bone collar to central clearing)
Endochondral ossification (from periosteal bud…)
Endochondrial ossification (peristeal bud to medullary cavity)
The medulla cavity
Endochondral ossification (cartilage in epiphysis to secondary ossification centre)
Endochondral ossification: After birth
Summary of endochondral ossification
Summary 2 (a different one) of endochondral ossification
Timeline of each stage of bone formation
How do bones e.g. long bones, increase their length?
How do bones e.g. long bones, increase their girth?
Length - endochondral ossification
Girth - intramembraneous ossification
Draw the structure and label it (of a long bone)
Different zones (in endochondral ossification)
R rich
P people
H hate
C counting
O osteoblasts/osteoclasts
Another diagram showing the different zones in endochondral ossification
Epiphysis of an adult long bone
Label the cells in this diagram of a spicule
What is the composition of bone?
Inorganic (65%)
Calcium Hydroxyapatite (calcium and phosphate, carbonate, chloride) and magnesium salts/aluminium salts
Inorganic component resists: bending and compression forces
- *Organic (35%)**
1. Collagen 1
2. GAGs and proteoglycans
3. Non-collagenous proteins - Osteocalcin
- Osteonectin
- Phosphoproteins
- Bone sialoprotein
- Bone morphogenic proteins
Organic component resists: pulling and tension forces
What are the roles of each of the cells in bone and what do these cells look like?
Osteoprogenitor: Undifferentiated cells - stem cell Inner layer of endosteum and periosteum
Osteoblast: Intermediate cells that cannot divided Inner layer of endosteum and spicules
Lay down new bone
Osteocyte: Terminally differentiated bone cell Trapped within osteon
No longer lay down matrix – tissue maintenance
Osteoclast: Huge cells (as many as 50 nuclei) Fused monocytes (WBCs)
On the surface of cortical bone (endosteum) Resorption of existing bone
Label this diagram
- Light blue is the cartilage
- Dark blue is the bone
Label this diagram
Compact bone - functional unit, structure, where all the cells are
The functional unit:
• Osteon
• Layers (lamellae) of compact mineralised collagen • Trap osteoblasts that produced the bone – osteocytes are terminally differentiated
• They sit in small depressions (lacunae)
• Send out long filipodia to ‘communicate’ with other osteocytes
• Osteoblasts are intermediate cells - these make osteopontin and osteocalcin and lay down new bone at the edges
• NB Osteoclasts are not found in cortical bone
• only on the edges (periosteum and endosteum) where they degrade bone
Osteoarthiritis
Osteoarthrititis (OA):
[age-related] degeneration
• mechanical failure of the articular cartilage - narrowing of the joint space - bone rubs againstbone
Rheumatoid arthritis (RA):
Autoimmune disease
• inflammation of a synovial membrane thickening of the joint capsule -subsequent damage to underlying bone and articular cartilage -both bone and cartilage disintegrate
Changes associated with rheumatoid arthirits
How does osteoarthiritis cause pain?
Hyaline (articular) cartilage and fibrocartilage menisci - permits smooth articulation
Osteoarthritic knee joint:
• Degeneration of the cartilage
• Narrowing of the joint space
• Growth of bony spurs (osteophytes) - causes inflammation and pain
What is an osteon? Where is the periosteum and endosteum? What and where are the central Haversian canals and perforsting volkmann’s canal? What is the canaliculus?
- Central (Haversion canal): Vertical in the middle of the osteon - The Haversian canal (osteonic canal) contains the bone’s blood vessels and nerve fibers. Contain blood vessels that nourish the cells of osteons.
- Perforating (Volkmann’s canal): horizontal, Connect central canals transversely and communicate with the bones surface and medullary cavity. Also contains, blood vessels and nerves
