Session 9 Flashcards
What are the three types of cartilage?
hyaline cartilage (glassy) elastic cartilage (elastic) fibrocartilage (fibrous)
Describe the composition of hyaline cartilage
the matrix contains type II collagen, which is thinner than type I so it has a fine mesh
hyaluronate proteoglycan aggregates bound to fine collagen matrix fibres
tough dense tissue often containing fluid- as much as 70% fluid
found at the ends of bones
Describe the composition of elastic cartilage
the matrix contains many elastic fibres and type II collagen in elastic lamellae layers
tough but flexible tissue- flexible because of the elastic fibres
Describe the composition of fibrocartilage
matrix contains lots of type I collagen because they are found in fibroblasts
small amount of collagen type II fibres
found in high compressibility places in between bones
What are chondrocytes and where are they found?
found in all the types of cartilage
lays down the fibres and matrices
How are chondrocytes present?
present as single cells or, if recently divided, in small clusters called isogenous groups
Why do the chondrocytes within isogenous groups separate?
they separate as they are laying down extracellular matrix
Where does hyaline cartilage remain?
at the articulating surface and at the epiphyseal plate until bone growth ceases
What does isogenous mean?
equal origin
Is hyaline cartilage vascular or avascular?
avascular- there is no blood supply
What does the loose matrix allow?
for the diffusion of materials
Describe the features of the extracellular matrix and how it is formed
chondrocytes produce and maintain the EM
the EM is solid and firm but also pliable (high water content) and therefore resilient to the repeated application of pressure- it will return to the original shape
What does hyaluronic acid do?
assists resilience to the repeated application of pressure
Where is the high resilience?
mature chondral region
How is compression prevented?
the proteoglycan structure in cartilage ground substance attracts a lot of water due to the many GAGs and hyaluronic acid
Each chondrocyte lies in…
a lacuna
What happens when chondrocytes are placed under pressure?
mechanical signals increase synthetic activity to release the pressure- makes more matrix which secretes into the extracellular space and causes chondrocytes to divide/ separate from each other which expands the size of the tissue
Where is the perichondrium and what does it contain?
it covers the margin of hyaline cartilage
contains elongated, fibroblast like cells that can develop into chondroblasts and then into chondrocytes
What is appositional growth?
growth from the periphery
What is interstitial growth?
growth from the centre
What type of tissue is the perichondrium?
a dense connective tissue
What is the structure of hyaline cartilage?
dense connective tissue
perichondrium
growing cartilage- appositional growth
What is the function of cartilage in the tracheal wall?
reinforces trachea and helps to protect and maintain the airway
Where is elastic cartilage found?
in the pinna of the ear
the Eustachian tube (connects ear to mouth)
the epiglottis
Fibrocartilage is a combination of…
dense regular connective tissue and hyaline cartilage
How are the cells arranged?
often seen distributed in rows
What is a difference of this cartilage to the others?
there is no surrounding perichondrium
Where is this fibrocartilage present in?
intervertebral discs
articular discs of sternoclavicular and temporomandibular joints
the menisci of the knee joint
pubic symphysis
What does the fibrocartilage act as?
a shock absorber (stops two bones banging together) and to resist shearing forces and twisting actions
Why does fibrocartilage appear haphazard?
because the cartilage moves in many different directions
What does cartilage do?
acts as a template for bone formation
How does bones develop in the foetus?
the long bones grow by endochondral ossification
How does the bone form from cartilage?
the cartilage is replaced by mineralised extracellular matrix to form bone
Where are the growth plates, the diaphysis, the metaphysis and the epiphysis found?
https://www.google.com/url?sa=i&url=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FIntroductory_and_General_Biology%2FBook%253A_General_Biology_(Boundless)%2F38%253A_The_Musculoskeletal_System%2F38.2%253A_Bone%2F38.2D%253A_Growth_of_Bone&psig=AOvVaw3adlM4tT5jKDL6yR0gfssk&ust=1605641996772000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCMCl2troh-0CFQAAAAAdAAAAABAD
Describe the long bone development at 5-6 weeks in a foetus
the initial cartilage model, the bone is just hyaline cartilage
Describe the long bone development at 6-8 weeks in a foetus
the collar of periosteal bone appears in the diaphysis region
compact bone grows all the way around the edge
Describe the long bone development at 8-12 weeks in a foetus
the central cartilage calcifies, the nutrient artery penetrates and supplies bone depositing osteogenic cells
the primary ossification centre is formed
Describe the long bone development at the postnatal stage
the medulla becomes cancellous bone
cartilage forms epiphyseal growth plates
epiphyses develop secondary centres of ossification
Describe the long bone development at the prepubertal stage
epiphyses ossify and growth plates continue to move apart, lengthening the bone
Describe the long bone development at the mature adult stage
epiphyseal growth plates replaced by bone
hyaline articular cartilage persists unless broken down by damage or age
How does bone increase in width/ girth?
using periosteal (intra-membranous) ossification
What are the 5 zones in an epiphyseal growth plate?
zone of... reverse cartilage proliferation hypertrophy calcified cartilage resorption
Describe the function of the cells in each zone
RC- no cellular proliferation
P- cells actively dividing to form columns, cells enlarge and secrete matrix
H- cells enlarge greatly
CC- enlarged cells begin to degenerate and matrix calcifies
R- small blood vessels and connective tissue invade the region occupied by dying chondrocytes, leaving the calcified cartilage as spicules between them
What is the key hormone in the growth of bone?
oestrogen
How does this hormone act on the growth?
during puberty, increases growth through activation of the alpha receptor isoform on maturity (ish 25 years) growth stops via activating the beta receptor isoform
Where are osteoids found?
They grow around the outside of the spicule, this traps the osteoblasts in the bone, these osteoblasts are now called osteocytes
What is the composition of the bone matrix?
organic and inorganic
35% and 65% respectively
What does the inorganic matrix consist of?
calcium hydroxyapatite (calcium and phosphate, carbonate, chloride) - this mineralises the collagen matrix and makes it into bone magnesium salts/ aluminium salts
What does the inorganic matrix do?
resists bending and compression forces
it gives bone its main strength
What does the organic matrix consist of?
collagen I
GAGs and proteoglycans
non collagenous proteins
What does the organic matrix do?
resist pulling and tension forces
Describe the osteoprogenitor
stem cell
inner layer of the endosteum and periosteum
Describe the osteoblast
intermediate cells that can’t be divided
inner layer of the endosteum and spicules
lay down new bone
Describe the osteocyte
terminally differentiated bone cells
trapped within osteon
no longer lay down matrix- they are involved in tissue maintenance
Describe the osteoclast
huge cells
fused monocytes
on the surface of the cortical bone (endosteum)
resorption of existing bone
What happens once the osteocytes are released?
they turn back into an osteoblast and make more bone
What are osteons?
lamellae (layers) of compact mineralised collagen
What do osteons do?
trap osteoblasts that produced the bone
sit in small depressions, lacunae
send out long filopodia to communicate with the other osteocytes
Osteoblasts are found in cortical bone
FALSE
found only on edges where they degrade bone
Osteoarthiritis (OA) degeneration and rheumatoid arthritis (RA) are the least common cartilage diseases
FALSE
most common
What is the main difference between OA and RA?
OA is a mechanical problem while RA is an autoimmune problem
What happens in OA?
the joint space narrows so bone rubs against bone which destroys the cartilage
What happens in RA?
there is inflammation of a synovial membrane which causes thickening of the joint capsule
there is subsequent damage to the underlying bone and articular cartilage, both the bone and cartilage disintegrate
antibodies destroy the cartilage and erode bones at the edges, where periosteum is and causes inflammation
How do these conditions cause joint pain?
due to the growth of bony spurs (osteophytes) as cartilage is gone which cause inflammation and pain
