[004] Cartilage And Endochondral Ossification Flashcards
What is cartilage and its purpose?
It is a structural and load bearing connective tissue. It maintains form and is flexible.
What are the mechanical properties of cartilage due to?
• Composite matrix (collagen and proteoglycans)
• Fluid flow to dissipate loading forces
In the trachea what are the hyaline cartilage rings surrounded by?
The rings are surrounded by fibrous perichondrium which contains type 1 collagen
What does hyaline cartilage stain with and what specifically is being stained?
Alcian Blue is the dye that stains blue and specifically stains the GAGs ( glycolaminoglycans) which are produced by chondrocytes
What colour does collagen stain with Alicia Blue?
Pink
What are the 2 ways that cartilage can grow?
Interstitial growth and appositional growth
What is interstitial growth?
This is when chondrocytes go through cycles of cell division to form clusters of daughter chondrocytes surrounded by ECM
What is appositional growth?
This is when there is an addition of new cells to the cartilage at the border of the cartilage and the perichondrium. These new cells arise from chondroblasts in the perichondrium which migrate into the cartilage and differentiate to form chondrocytes and produce ECM
What is cartilage composed of?
• Chondrocytes
• ECM - fibrous component ( collagen type 2)
NB the fibrous component of of the cartilage ECM can be altered via the addition of elastin or type l collagen
• GAGs and proteoglycans (ground substance)
What are the four properties of cartilage?
- Permeable: stiff in compression due to proteoglycan aggregates
- Fibrous network: can resist high tensile stresses - collagen
- Fluid: flows under load or deformation to help dissipate forces
- High swelling pressure: matrix is swollen with water due to protcoglycan aggregates
What are the 2 types of cartilage?
- Permanent cartilage: present in adult life eg. Hyaline cartilage in trachea and bronchioles, elastic cartilage in ear, articular cartilage in joints
- Temporary cartilage: present during growth and development big. Epiphyseal growth plate, Meckel’s cartilage (forms jaw), base of skull
What type of cartilage does the image show?
This shows small discontinuous rings of hyaline cartilage swrounding the bronchioles to keep them patent
What are the 3 types of cartilage joints?
- Synovial: freely moveable (articular cartilage)
2 Symphysis: (bone-cartilage- fibrous tissue-cartilage-bone). These allow slight movement. Eg. Pubic symphysis - Synchondrosis: (bone-cartilage-bone) negligible movement eg. Spheno-occipital synchondrosis at the skull base
What colour does articular cartilage stain and how does it appear?
It stains a lighter pink than fibrous tissue and appears more shapeless
Where is mineralised cartilage found?
It is found between unmineralised cartilage and bone at joints and has an irregularly shaped border with bone but a smooth border with the unmineralised cartilage
What is mineralised cartilage?
It is particular cartilage containing calcium phosphate hydroxyapatite (so is harder than unmineralised cartilage)
Does mineralised or unmineralised cartilage stain darker?
Mineralised stains darker
What is the difference between bone marrow, bone and cartilage?
Bone marrow: contains lots of blood vessels
Bone: contains vascular channels
Cartilage: contains NO blood vessels
What i the difference between hyaline and particular cartilage?
They have the same appearance except articular cartilage lacks a fibrous perichondrium on its articular surface to minimise friction between the articulating surfaces during movement.
What happens to the tidemark zone as the individual ages?
The tidemarle zone advances towards the articular surface due to increased calcification of the cartilage.
True or false: collagen is a double stranded helix?
False, it is a triple stranded helix (3 alpha chains)
How is type I collagen formed and give examples.
This is formed as fibrils which aggregate to form fibres which are visible under a light microscope eg. Bone, skin, tendons
How is type 2 collagen formed and give examples.
It is found as fibrils which form a fine meshwork (not visible under a light microscope). Eg. Cartilage, vitreous humour
How is type 3 collagen formed and give examples.
Exists as fibrils which aggregate to form reticular fibres which form a coarse mesh to hold cells together eg. Blood vessels, skin
How does collagen type 4 form?
Forms a sheet like network that forms the structural basis of the basal Lamina
Why do GAGs form a thick jelly like substance?
As specific sugar residues are modified through the addition of COO- and this negative charge makes the molecule hydrophilic and attracts water (only in cartilage)
What is hyaluronon?
A joint lubricant in synovial fluid but also found in ECM
What are proteoglycans?
These are formed when GAGs are attached to a core protein
How are proteoglycans formed?
GAGs can be struck onto a core of hyaluronan to form large proteoglycan aggregates
What are the 2 processes of ossification?
- Endochondral ossification
- Intramembranous ossification
What is endochondral ossification?
Occurs in long bones that are formed initially as a cartilage model and later replaced by bone
What is intramembranous ossification?
Occurs in flat bones where osteoblasts differentiate from progenitor and form bone directly with no cartilaginous precursors/framework
What is the full process of endochondral ossification?
- Initially a cartilage framework is established
- Osteocytes in the centre of the bone convert cartilage to bone.
- Chondrocytes therefore become mineralised - this all occurs in the primary ossification centre
- This mineralisation sends signals to trigger anglogenisis in the bone
- The penetration of these blood vessels destroys the cartilage
- Secondary ossification centres form at either end of the bone
- Epiphyseal growth plate exists between the primary and secondary ossification centres
- Vessels form in the secondary ossification centres and destroy the cartilage here
- Post puberty the secondary centres ossify due to gondal steroids
- These steroids cause the growth plater to disappear connecting the primary and secondary marrow cavities
- Cartilage remains at the tips of the bone
What is the process that occurs in growth plates?
- There is no perichondrium and chondrocytes are in columns running between ossification centres
- Chondroblasts are found in the growth plate near the secondary centre
- When activated the chondroblasts divide and migrate towards the bone marrow whilst synthesising the ECM
- As cells more towards the bone marrow they enlarge and begin to calcify
- At the boundary between the growth plate and bone marrow, marrow cells attack the edge of the growth plate destroying the hypertrophied chondrocytes
What is the full process of intramembraneous ossification?
It doesn’t use a cartilage model. The progenitor cells within cartilage differentiate to form osteoblasts which surround the bone matrix and release ostloid. Osteoblasts then differentiate to become osteocytes and the matrix is then mineralised to form bone.
Why is vitamin D important for bones?
Ensures that sufficient calcium is absorbed into the blood stream via the gut
What are some vitamin D deficiency diseases?
Rickets - the growth plate widens, fails to mineralise and is not replaced by bone.
What is osteomalacia?
Intramembraneous ossification occurs and newly formed bone matrix during the turnover process fails to mineralise, causing bones to soften leading to deformities and fractures.
What is osteoarthritis?
Fatigue failure / abrasion of collagen meshwork and loss of proteoglycan aggregates. This leads to cartilage erosion and bony outgrowths in an attempt to stabilise the joints despite cartilage damage leading to bone deformities
What causes osteoarthritis?
It could be caused by the Tidemark zone. The advancing irregular mineral tidemark migrates towards the articular surface. It acts in an abrasive manner and damages soft cartilage as the joint articulate by pressing the soft cartilage against the sharp mineral protrusions of the tidemark zone which shreds the cartilage.
