TOB L7 Flashcards
Describe cartilage and where it is commonly found
Form of connective tissue
Found at most joints
Strong + deformable structures
State adaptations of cartilage
Pliant (flexible)
resists compression
Avascular
Not innervated
State the 2 types of cartilage cells
Chondroblasts
Chondrocytes
Which cells produce ECM in cartilage
Chondroblasts
Chondrocytes
Histology showing hyaline cartilage of the trachea
Isogenous (nest) cells
Perichondrium
Chondroblasts
State the 3 types of cartilage
- Hyaline cartilage -
- Elastic cartilage - contains lots of elastic fibres, difference from hyaline cartilage
- Fibrocartilage - ECM as lots of Type I collagen - difference from hyaline cartilage
Describe the composition of hyaline cartilage
ECM contains proteoglycans, hyalaronic acid, type II collagen
State a difference between hyaline and elastic cartilage
Elastic cartilage contains elastic fibres
State a difference between hyaline and fibrocartilage cartilage
ECM of fibrocartilage contains type I collagen fibres
State locations of hyaline cartilage
- Articular cartilage - found at ends of bones + moveable joints
- Costal cartilages - connect ribs to sternum
- Larynx and trachea
Describe the features of hyaline cartilage
- Covered by fibrous perichondrium (except for articular surface of synovial joints)
Describe the composition of abundant ECM in hyaline cartilage
- Type II collagen - collagen in hyaline cartilage forms fibrils but does not assemble into fibres (contributes to unique properties of hyaline cartilage) - STRUCTURAL SUPPORT
- Hyaluronic acid - molecule which holds lots of water. Keeps hyaline cartilage well hydrated, provides resilience to tissue under pressure. Makes it pliable (flex + absorb mechanical forces)
- GROUND SUBSTANCE : NON CELLULAR COMPONENT OF ECM: Glycosaminoglycans (GAGs, including hyaluronic acid + proteoglycans) to Collagen Ratio: Large ratio of GAGs to collagen in ECM. Facilitates diffusion of substances between chondrocytes (cartilage cells) and blood vessels surrounding cartilage
- Type II collagen
- Water
- Ground substance
State key properties of hyaline cartilage ECM
- Hyaluronate Proteoglycan Aggregates:
molecular complexes formed by binding of hyaluronic acid + proteoglycans.
Contribute to resistance to deformation of hyaline cartilage.
Allows hyaline cartilage to withstand compressive forces + maintain structure, providing support to joints - Negative gel + hydrated gel formation
GAGs (hyaluronic acid)/ carries negative charges on surface.
Negative charges strongly attract polarized water (H2O)
Attraction leads to formation of hydrated gel within cartilage
Hydrated gel contributes to ability to absorb + distribute mechanical forces, allowing to cushion joints
Describe the growth process of hyaline cartilage
- Perichondrium + appositional growth (hyaline cartilage increasing in size by adding new layers to its surface): chondroblasts in perichondrium add new cartilage to outer surface of existing cartilage to increase size by adding new layers
- Dividing cells + isogenous groups
Dividing cells within cartilage form isogenous groups (clusters of cells derived from the same parent cell). Cells contribute to territorial + inter-territorial matrix production - Territorial + inter-territorial matrix
matrix produced by chondrocytes can be categorised into territorial + inter-territorial matrix. Territorial matrix surrounds individual lacunae (spaces where chondrocytes reside). Inter-territorial matrix lies between lacunae.
Describe the effect of pressure and stress on hyaline cartilage
Creates mechanical + electrical signals
This increases chondrocyte activity
Osteoarthritis
Most common form of arthritis
Prevalence increasing with age
Results from focal (centre) + progressive hyaline articular cartilage loss with changes to underlying bone
Soft tissue structures in + around joint affected
CAUSES:
-severe joint injury (fractures of articular surfaces, tears of menisci
-obesity
Osteoarthritis leads to patients having total knee + total hip replacements
Describe the prevalence and age of osteoarthritis
Most common form of arthritis
Prevalence increases with age
Describe characteristics of osteoarthritis
- Focal (localised) + progressive loss of hyaline articular cartilage (covers ends of bones with joint)
- Changes in underlying bone structure as result of cartilage loss
- Soft tissue structures in + around joint also affected
Describe causes + risk factors osteoarthritis
CAUSES:
1. Severe joint injuries including fractures of articular surfaces + tears of menisci (cartilage discs in knee joint)
2. Obesity
RISK FACTORS
1. Total knee replacement
2. Total hip replacement
X-Ray shows arthritis of knee joint
State locations of elastic cartilage
- External ear pinna
- External acoustic meatus
- Auditory tube
- Epiglottis
Histology showing elastic cartilage from the epiglottis
Elastic fibres lying in ECM
Provide elasticity + increased resilience
(more than hyaline cartilage)
State locations of Fibrocartilage
1.I ntervertebral discs
2. Articular discs of 3.sternoclavicular and temporomandibular joints
4. Menisci of knee
5. Pubic symphysis
6. Entheses (between tendon and bone)
FIBROCARTILAGE HAS NO PERICHONDRIUM
Histology of fibrocartilage in intervertebral discs
In the annulus fibrosus,
chondrocyes in lacunae
are embedded in large
bundles of type I collagen
fibres.
This provides a tough,
shock absorbing structure.
In some regions, e.g. the
pubic symphysis or menisci
of the knees, more
cartilaginous matrix can be seen
Describe how fibrocartilage in intervertebral discs provides a tough shock absorbing structure
- In annulus fibrosus, chondrocytes in lacunae embedded in large bundles of type I collagen fibres
- This provides a tough, shock absorbing structure
Meniscal damage
1.
Describe the composition of fibrocartilage
Dense regular connective tissue
Hyaline cartilage (therefore, contains fibroblasts + chondrocytes)
State properties of fibrocartilage
resilience to act
as a shock absorber and to resist
shearing forces.
FIBROCARTILAGE HAS NO PERICHONDRIUM - we can use this to recognise it
State the role of fibrocartilage in the menisci of the knee
Menisci of knee formed of fibrocartilage discs separating femur and tibia
Menisci Prevent degeneration of articular cartilage underneath
State a common cause of meniscal lesions in young people
Sport related injury
includes trauma, twisting or direct impact on knee leading to damage of menisci
State a common cause of meniscal lesions in middle aged people
Long term degeneration of articular cartilage underneath
overtime, wear and tear of menisci, due to repetitive movements, ageing
Describe the position of the menisci
Between femur (thigh bone)
and tibia (shinbone) in knee joint
State the functions of menisci
Fibrocartilage
Cushions knee joint
Stabilises knee during movement
By distributing weight
Also by acting as shock absorber
Prevents degeneration of articular cartilage (covering ends of femur + tibia joint)
Act as cushions + stabilisers in knee joint
Help distribute weight, absorb shock, provide stability during movements
Prevents degeneration of articular cartilage that covers ends of femur and tibia in joint
State functions of bone
Strength + rigidity allows forceful muscle contractions to result in movement
Provides protection for internal structures
Highly vascular + innervated
Adapts to changing mechanical demands
Regenerates following injury
Mineral storage
Blood cell formation
Bone divisions and classifications
Axial Skeleton:
- Skull
- Vertebral column
- Ribs
- Sternum
- Hyoid
Appendicular Skeleton
everything else
Shapes of bones
Long
Short
Flat
Irregular
Sesamoid
Pneumatic (bones containing air filled spaces / cavities)
Describe the composition of bone
Inorganic component: Calcium Hydroxyapatite Crystals. contribute to strength + hardness of bones. Presence of minerals (esp calcium) provides bone with solid + rigid structure, resistant to compression
Organic component: Type I collagen
Collagen is a fibrous protein that imparts flexibility + resilience to bone. Provides elasticity + bone resist bending + twisting forces
Describe the types of mature bone structure
2 types of mature bone structure:
- Cancellous (spongy) Bone
-spongy, porous structure with open spaces
-lighter weight compared to compact bone
-usually located in ends of long bones, within interior bones, areas where bone is not subjected to high mechanical stress
-FUNCTION: FLEXIBILITY + CUSHIONS. CONTAINS SPACES THAT HOUSE BONE MARROW, WHERE BLOOD CELLS ARE PRODUCED - COMPACT (cortical) Bone: dense + solid with more homogenous structure.
Heavier + stronger compared to cancellous bone
LOCATION: compact bone forms outer layer of all bones + shafts of long bones
FUNCTION: structural support, strength, protection of internal components incl bone marrow
Describe the organisation of compact (cortical) bone
Osteon - basic structural unit of compact bone (cylindrical)
Haversian (Central) Canal:
central channels within osteon, carries blood vessels, lymph vessels, nerves
Volkmann’s Canal (perforating canals) - connect haversian canals. Allow for passage of blood vessels, lymph vessels + nerves from periosteum to haversian (central) canals
Lamellar Structure of Osteon:
osteon has a lamellaer (layered) structure, with concentric rings of mineralized matrix called lamellae. Lamellae surround Haversian canal + provide strength to the osteon
Slippage Panes:
The lameller structure of the osteon provides slimage planes. Allows deformation + flexibility within bone. While bone is rigid, flexibility important for adapting to mechanical stress
Cortical bone surrounded by layer of fibrous connective tissue called periosteum
Periosteum important for bone health, growth. Contains blood vessels, nerves, cells involved in bone formation + repair. Attachment point for tendons and ligaments
Describe the role of canaliculi in an osteon
Canaliculi = channels extending from osteocytes
Connect neighbouring osteocytes, allowing communication between them
State where osteocytes are found within an osteon
Mineralised matrix
Explain the communication process between neighbouring osteocytes
- Osteocytes have slender cytoplasmic processes - extensions
- Reach out to adjacent osteocytes via canaliculi (tiny channels)
- Allows osteocytes to maintain contact with each other, facilitate exchange of nutrients + signalling molecules
- Slender Cytoplasmic processes connect with each other via gap junctions
- Gap Junctions enable passage of nutrients between adjacent osteocytes
- Slender Cytoplasmic processes connect to Haversian canals
- This allows osteocytes to receive nutrients + signals from blood vessels in Haversian canal.
Gap Junctions
Specialised protein channels
Allow direct communication between cells
Describe the organisation of spongy (cancellous) bone
- No Haversian / Volkmann’s canals
- Osteocytes reside in lacuna (small spaces or cavities within the bone matrix) between lamellae (same as cortical)
- Lamellae are more irregular than in cortical
Which cells carry out bone remodelling in spongy bone?
Bone remodelling - removal of old bone tissue, formation of new tissue
1. Osteoblasts
2. Osteoclasts
State the location of osteoblasts and osteoclasts in spongy bone
Surface of trabeculae
H&E photomicrograph of a section of
decalcified spongy (cancellous) bone
Describe the process of bone remodelling
- Process starts with CUTTING CONE, group of osteoclasts (specialist cells for breaking down + resorbing bone tissue). CUTTING CONE ACTIVELY REMOVES OLD DAMAGED BONE
- REVERSAL ZONE: this region contains osteoprogenitor cells, undifferentiated cells, have potential to become osteoblasts. Osteoprogenitors involved in transition phase between bone resorption + bone formation
- Closing cone: Osteoblasts (bone-forming cells) secrete organic components of bone (osteoid). Osteoid = unmineralised organic matrix of bone, provides framework for mineralization
- Apiogenesis - formation of blood vessels. Important because supplies necessary nutrients + oxygen to the actively remodelling bone tissue
State the role of an osteoclast
Break down bone during resorption phase
State the role of an osteoblast
Lay down new bone during formation phase by secreting osteoid
State the role of osteocytes
Mature osteoblasts
Become embedded in mineralised matrix
Metabolically active + maintain bone tissue
Describe the bone remodelling unit
Consists of
- Cutting zone
- Reversal zone
- Closing cone
Photomicrograph of a cutting
cone (H&E)
Describe which factors influence the pattern + extent of bone remodelling
- Mechanical loading: forces + stresses experienced by bone during activities (weight bearing + movement). Osteoclasts are sensitive to mechanical loading - respond to mechanical forces applied to bone tissue
- Reduced gravitational forces: Bone resorption increases when gravitational forces reduced. Eg situations incl: long period of bed rest, space travel, reduced weight bearing
Age: bone remodelling decreases with age. Increasing age = shift in balance between bone resorption + bone formation = changes in bone density + structure
Increased sport activity + bone hypertrophy - increase in physical activity can lead to bone hypertrophy (increase in bone size / mass - increased cortical bone thickness)
Describe the process of bone repair after fracture
Bone has a balance between flexibility + rigidity. Balance allows ability to withstand forces + resist fractures
Lamellae able to slip relative to each other. Allows bone to disperse forces. When external force is applied to bone, lamellae can adjust positions, distributing forces + preventing concentrated stress points that could lead to fractures
Fractures occur when forces applied to bone are too strong for its structural integrity to withstand
If the forces exceed the bone’s ability to flex + redistribute stress through the slipping of lamellae, it results in fracture
Describe the stages of bone fracture repair
- Haematoma: when bone fractures, blood vessels around + within fractured area are torn + bleed = accumulation of blood to area
leads to formation of blood clot (haematoma)
Haematoma stabilises fractured bone fragments - Soft (fibrocartilage callus): Clot is removed by macrophages + replaced by mass of procallus tissue comprised of fibroblasts + collagen
- Hard (bony) callus: Fibrocartilage callus formed in previous step further transformed into hard bony callus. Due to invasion of callus by blood vessels + osteoblasts
Callus is invaded by blood vessels + osteoblasts. Fibrocartilage is gradually replaced by woven bone (immature bone tissue, provisional structure, gives stability to fractured area)
- Remodelling: Woven bone remodelled as compact + spongy bone
X-Ray showing stages of fracture repair
