9. Cartilage and bone Flashcards
Where is cartilage found?
Between joints
Which cell gives rise to all the specialised connective tissues?
Mesenchymal stem cell
What are the 3 types of cartilage
Hyaline cartilage
Elastic cartilage
Fibrocartilage
What do all the cartilage types have?
All have matrix containing proteoglycan and hyaluronic acid
All have chondrocytes
All the cartilages contain a lot of fluid
In hyaline cartilage, what does the matrix contain?
Matrix contains type II collagen. The hyaluronate proteoglycan aggregates are bound to the fine collagen matrix fibres – dense tissue often containing fluid.
Which cells are present on hyaline cartilage?
Only chrondocytes
How are chrondocytes formed?
Grows from perichondrial cells - cells on the edge- fibroblast like precursors. As they develop, they develop into chrondoblasts. They divide and produce chrondocytes which makes up the matrix.
Which are the only cells that can divide in cartilage tissue?
Chrondoblasts
How are chrondocytes present?
Chondrocytes are present singly or, if recently divided in small clusters called isogenous groups
What happens to the chrondocytes in isogenous groups as they lay down extracellular matrix?
The chondrocytes within the isogenous groups separate as they lay down extracellular matrix
Why is hyaline cartilage needed for bones?
- In early fetal development hyaline cartilage is the precursor model of those bones that develop by endochondral ossification
- As long bones develop, some hyaline cartilage remains at the articulating surface, (and also at the epiphyseal plate until bone growth ceases) - parts of the rib cage, nose, and in the trachea, bronchi and larynx
What is the function of chrondocytes?
They produce and maintain the extracellular matrix
What does each chrondocytes lie in?
A lacuna
How do the chrondocytes produce the extracellular matrix?
Chrondocytes grow until they burst and release their content containing fibres and GAGs/hyaluronic acid into the extracellular matrix
What is the function of hyaluronic acid?
Hyaluronic acid assists resilience to the repeated application of pressure
What are not present in cartilage?
Blood vessels - matrix allows diffusion of material from other tissue
What is the Proteoglycan structure in cartilage ground substance?
- Have lots of collagen
- Have About 100 hyaluronate proteoglycan aggregates per collagen fibril
- Makes a very stiff gel-like substance
Where in the body is hyaline cartilage found?
- Cartilages in nose
- Articulate cartilage of a joint
- Costal cartilage
- Larynx
- Trachea
- Lung
What is appositional growth?
Growth of hyaline cartilage from the periphery
What is interstitial growth?
Growth of the hyaline cartilage from the centre
What is perichondrium?
the dense connective tissue that envelops cartilage where it is not at a joint.
What does the perichondrium contain?
Contains elongate, fibroblast-like cells that can develop into chondroblasts and then into chondrocytes
The hyaline cartilage extracellular matrix is highly hydrated, what is the advantage of this?
Water is non-compressible and so permits resilience to increased loads
Describe the structure of the tracheal wall which contains hyaline cartilage
- Tube formed by C-shaped tracheal cartilages (HYALINE CARTILAGE)
- Cartilage in tube reinforces trachea and helps to protect and maintain the airway
- Lined with pseudostratified ciliated epithelium
What does the matrix of elastic cartilage contain?
Matrix contains many elastic fibres and elastic lamellae (layers) – tough but flexible tissue.
What cells do elastic cartilage contain?
Only chrondocytes
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
Describe the layers found in the pinna of the ear from the muscle to the epidermis
Muscle Adipose tissue - white coloured Elastic cartilage Fibrocollagenous tissue Dermis Epidermis
What does the matrix of fibrocartilage contain?
Matrix contains lots of type I collagen fibres
What cells are present in fibrocartilage?
Chondrocytes and fibroblasts
What is fibrocartilage a combination of?
Fibrocartilage is a combination of dense regular connective tissue and hyaline cartilage
How are the cells in fibrocartilage often distributed?
The cells are often seen to be distributed in rows
Does fibrocartilage contain perichondrium?
There is no surrounding perichondrium
Where is fibrocartilage present?
Present in intervertebral discs, articular discs of the sternoclavicular and temporomandibular joints, the
menisci of the knee joint and in the pubic symphysis
What is the function of fibrocartilage?
The fibrocartilage has the resilience to act as a shock absorber and to resist shearing forces
What does hyaline cartilage act as a template for?
Bone formation of long bones by endochondral ossification
What is the middle section of long bone called?
Diaphysis
What is the end bit of long bone called?
Epiphysis
What is the small section between diaphysis and epiphysis called?
Metaphysis
What are the growth plates in long bone called?
Epiphyseal growth plates
What are the 5 classification of long bones?
- Long
- Short
- Flat
- Irregular
- Sesamoid (sesame seed-like)
What are the two bones that bones are made of?
Cancellous/ spongy bone
Compact/cortical bone
Describe cancellous/spongy bone
Cancellous/spongy bone forms a network of fine bony columns called trabeculae or plates to combine strength with lightness. The spaces are filled by bone marrow.found in the centre of bone
Describe compact/cortical bone
Compact/cortical bone forms the external surfaces of bones and comprises ~80% of the body’s skeletal mass. Compact bone consists of closely packed osteons or haversian systems. The osteon consists of a central canal called the haversian canal, which is surrounded by concentric rings (lamellae) of matrix. Between the rings of matrix, the bone cells (osteocytes) are located in spaces called lacunae. Small channels (canaliculi) radiate from the lacunae to the haversian canal to provide passageways through the hard matrix. In compact bone, the haversian systems are packed tightly together to form what appears to be a solid mass. The haversian canals contain blood vessels that are parallel to the long axis of the bone. These blood vessels interconnect, by way of perforating (Volkmann’s )canals, with vessels on the surface of the bone.
What are the two types of bone marrow?
Red marrow
Yellow marrow
Where is red marrow found?
Only found in spongy bone.
What do red marrow contain?
Full of developing blood cells
What is the function of red marrow?
To replenish cells in the blood (haemopoiesis)
How is the blood supply in red marrow?
Rich blood supply
What do yellow marrow contain?
Full of adipocytes
How is the blood supply in yellow marrow?
Poor blood supply
What is the function of yellow marrow?
Shock absorber and energy source. Can convert to red marrow
What does each trabeculum in cancellous bone consist of?
Each trabeculum consists of numerous osteocytes embedded within irregular lamellae of bone
Osteoblast and osteoclasts on their surfaces act to remodel them.
What are osteoprogenitor cells
Mesenchymal stem cells that have the capability to become many different cell types. Undifferentiated cells - stem cell
Found in Inner layer of endosteum and periosteum
What are osteoblasts?
Intermediate cells that cannot divided.
Found in Inner layer of endosteum and spicules.
Lay down new bone called “osteoid” which is made of bone collagen and other protein. - secretes organic components of matrix
Deposit new Osteoid in response to demand, thickening bone.
What are the identifying features of osteoblasts?
Single nucleus, sits on edge of bone surface
What are osteocytes?
Terminally differentiated bone cell.
Trapped within osteon
No longer lay down matrix – tissue maintenance
Regulates existing bone.
As osteoblasts deposit new bone, some become trapped, becoming osteocytes and supply nutrition to bone
What are the identifying features of osteocytes?
Cytoplasmic projection, single mucleus
What are osteoclasts?
Huge cells (as many as 50 nuclei).
Fused monocytes (WBCs). - Macrophage/monocytes cell line.
On the surface of cortical bone (endosteum).
Resorption of existing bone - Erode and recycle bone matrix.
Phagocytic cells.
Work with osteoblasts to maintain calcium homeostasis, also responds to mechanical stress
What are the identifying features of osteoclasts?
Large, multinucleate
Describe long bone development by endochondral ossification
- Initial hyaline cartilage model
- Collar of periosteal bone appears in the shaft
- Central cartilage calcifies. Nutrient artery penetrates supplying bone-depositing osteogenic cells. Primary ossification centre formed.
- Medulla becomes cancellous bone. Cartilage forms epiphyseal growth plates. Epiphyses develop secondary centres of ossification.
- Epiphyses ossify and growth plates continue to move apart, lengthening bone
- Epiphyseal plates replaced by bone (when adult)hyaline articulations cartilage persists.
Describe how osteoblasts make bone
- Osteoblasts are the cells that are proliferating and making matrix. The ones that are laying down collagen 1. Osteoblasts are on the edge of the developing bone.
- As they lay down the collagen and it becomes ossified - becomes mixed with minerals to become bone, the osteoblast becomes trapped and is then called osteocytes.
- The osteocytes is the fully differentiated cell in this lineage.
- The osteocytes have filopodia which helps to find other osteocytes and the edge of the bone. This is needed because there are not enough blood vessels in this part of the bone to give the cells the nutrients they need. Therefore the osteocytes receives its nutrients and loses its waste through other osteocytes.
What is the composition of bond divided into?
Divided into matrix and cells.
What is the matrix of bone divided into?
Organic and inorganic
What does the inorganic matrix of bone contain?
Calcium Hydoxyapatite (calcium and phosphate, carbonate, chloride) and magnesium salts/aluminium salts
What makes up the organic part of matrix of bone?
- Collagen 1
- GAGs (mucopolysaccharides) and proteoglycans
- Non-collagenous proteins
What does the inorganic component of bone matrix resist?
bending and compression forces
What does the organic component of bone matrix resist?
pulling and tension forces
What are the cells present in bone?
Osteoprogenitor
Osteoblast
Osteocyte
Osteoclast
What is osteon?
Layers (lamellae) of compact mineralised collagen.
They Trap osteoblasts that produced the bone –
osteocytes are terminally differentiated
Osteons are cylindrical structures that contain a mineral matrix and living osteocytes connected by canaliculi, which transport blood. They are aligned parallel to the long axis of the bone. Each osteon consists of lamellae, which are layers of compact matrix that surround a central canal called the Haversian canal
What is the middle of the osteon called?
Haversian canal
What does the haversian Canal have?
Blood vessels and nerves
What is osteoid?
the unmineralized organic component of bone. (90% collagen, 10% ground substance)Becomes bones when mineralised
What is the functional unit of compact bone?
Osteon
What does the osteon sit in?
They sit in small depressions (lacunae)
How do osteocytes communicate with the osteocytes?
Send out long filipodia to ‘communicate’ with
other osteocytes
What channel connects Haversian canals together?
Perforating/Volkmann’s canal
Are osteoclasts found in cortical bone?
Osteoclasts are not found in cortical bone. only on the edges (periosteum and endosteum)
where they degrade bone
What is the endosteum?
Where the spongy bone finishes and meets critical bone
What is the periosteum
The edge of the bone
What two proteins do osteoblasts make?
osteopontin and osteocalcin
What is the most common cartilage/bone disease?
Osteoarthritis and rheumatoid arthritis
Describe osteoarthritis
: [age-related] degeneration
• mechanical failure of the articular cartilage -
narrowing of the joint space
- bone rubs against bone
Describe rheumatoid arthritis
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
How does osteoarthritis cause joint pain?
Normal knee joint:
Hyaline (articular) cartilage and fibrocartilage menisci
- permits smooth articulation
Osteoarthritic knee joint: • Degeneration of the cartilages • Narrowing of the joint space, • Growth of bony spurs (osteophytes) - causes inflammation and pain
