Session 9 ILOs - Cartilage and Bone Flashcards
Describe the composition of (general) cartilage in terms of its cells and extracellular components
Composition - Chondrocyte cells:
- Chondrocytes
Chondroclasts
Composition - Extracellular components:
Extracellular matrix composed of proteoglycans and hyaluronic acid
Classify the 3 major types of cartilage and describe the structural differences between them
- Hyaline cartilage = MOST COMMON
- Contains type 2 collagen fibres
- Has hyaluronate proteoglycan aggregates bound to fine collagen matrix fibres
- Tough dense tissue (often containing fluid up to 70% fluid) - Elastic cartilage
- Contains mainly elastic fibres and type 2 collagen (in layers)
- Tough but flexible (due to elastic fibres) - Fibrous cartilage
- Contains lots of type 1 collagen & small amount of type 2 collagen fibres
- Tough and durable
Relate the different anatomical distribution of the 3 major types of cartilage to their different functions
- Hyaline cartilage
Properties: Tough dense tissue (often containing fluid up to 70% fluid)
Found: Intercostal, nose, pubic symphysis, end of all bones that articulate (e.g. knee/wrist/elbow joints)
Function: Provides stiff but flexible support and reduces friction - Elastic cartilage
Properties: Tough but flexible (due to elastic fibres)
Found: External ear, auditory canal (Eustachian tube) and epiglottis
Function: Provides support and tolerates distortion - Fibrous cartilage
Properties: Tough and durable
Found: Pads within knee joint, in-between pubic bones of pelvis and intervertebral discs
Function: Resists compression and prevents bone to bone contact (limits movement)
Describe the composition of bone in terms of its cells and extracellular components (organic and inorganic)
Bone composition - Cells:
- Osteoprogenitor cells
- Osteoblasts
- Osteocytes
- Osteoclasts
Bone composition - Extracellular components (organic and inorganic):
Organic - collagen, GAGs + proteoglycans and non-collagenous proteins (resists pulling and tension forces)
Inorganic - calcium and phosphate (resists bending and compression forces)
Describe the microstructure of compact (cortical) and spongy (cancellous/trabecular) bone
Compact (cortical) bone:
Compact bone is layered with layers of compact mineralised collagen, with an osteon which forms the functional unit. Osteocytes are terminally differentiated and sit within lacunae depressions. Contain Haversian an Volkmann’s canals which carry blood vessels, lymph vessels and nerves.
Spongy (cancellous/trabecular) bone:
Spongy bone is full of trabeculae structures (tear drop shaped), with the spaces being filled with bone marrow and blood vessels. Does NOT contain Haversian an Volkmann’s canals.
Explain how bone is a living tissue, how it is formed and how it undergoes remodelling and repair
Bone is a living tissue because it’s dynamic and is constantly remodelling itself and can undergo growth and repair
Bones can be formed in 2 ways:
1. Endochondral ossification e.g. growth at ends - formation of long bones from a cartilage template
- Intramembranous ossification e.g. growth in middle - formation of bone from clusters of MSC in the centre of bone (tracecular bone)
Explain the importance of vitamin D in normal bone stability
Vitamin D is very important for bone stability because vitamin D is key in the resorption of calcium from the gut (vitamin D is absorbed in the gut or synthesised in the skin)
Vitamin D deficiency can lead to lower mineralisation and increased osteoid
Needed in children to help form strong bones (Rickets if Vitamin D insufficiency) and in adults to maintain strong bones (Osteomalacia if not)
Describe the cellular processes involved in bone repair following a fracture
- Haematoma formation
Because blood vessels are broken, a haematoma forms (clotted blood) so swelling and inflammation occurs causing pain. Phagocitic cells and osteoclasts remove dead/damaged tissue. Macrophages eventually remove blood clot. - Fibrocartilaginous callus formation (soft callus)
New blood vessels infiltrate and a procallus of granulation tissue develops. Fibroblasts produce collagen fibres and some fibroblasts become chondroblasts that produce a sleeve of hyaline cartilage. And osteoblasts from nearby begin to produce spongy bone - Bony callus formation (hard callus)
Trabeculae have developed and all cartilage is replaced by spongy bone by endochondrial ossification (everywhere - no cortical bone). Blood vessels have reconnected. - Bone remodelling
Spongy bone is remodelled into cortical bone, especially where the shaft walls used to be. Excess spongy bone (sticking out at edge) is removed by the osteoclasts = same shape as before break!
Describe the genetic basis and phenotypical changes in osteogenesis imperfecta
Osteogenesis imperfecta:
- Occurs due to a mutation in the COL1A gene (produces type I collagen). So type I collagen fibres are incorrectly produced
- Weak bones are therefore produced = increased fracture risk
- Leads to a shortened height and stature
Describe the features of bones affected by rickets and osteomalacia, the difference between the two conditions and explain the importance of dietary and behavioural factors in their prevention
Rickets (children):
- Due to vitamin D deficiency in childhood, leads to poor calcium mobilisation and ineffective mineralisation
- Bowed leg appearance due to weak and soft bones leading to a short stature and painful to walk
Osteomalacia (adults):
- Due to vitamin D deficiency later in life, leads to lower mineralisation and therefore increased osteoid (from lack of mineralisation)
- Increased risk of fractures, especially a particular weakness 1/3 way down the bone
Differences:
- Rickets mainly affects children whereas osteomalacia affects adults
- Rickets is a disorder of impaired mineralization of cartilaginous growth plates whereas osteomalacia is a disorder of impaired mineralization of the osteoid
Describe the radiological and structural changes occurring in osteoporosis
The outer surfaces of bony trabeculae (of spongy bone) are regularly remodelled but this is incomplete in osteoporosis
As the osteoblasts fill in the cavity left by the osteoclasts, the depression (lacunae) is incompletely filled which leads to weakness and holes in the bones
This can lead to compression fractures EXAMPLE: in the vertebral bodies (compression of the spine)
List the most common risk factors for osteoporosis
Common risk factors:
- Insufficient calcium intake (recommended 700mg/day)
- Exercise - important if individual is bed bound or inactive
- Cigarette smoking (mainly in women)
Outline the cause and morphological features of achondroplasia
Achondroplasia is caused by a mutation in the FGF3 receptor gene
FGF promotes collagen formation from cartilage = only affects endochondral ossification and NOT intramembranous ossification
Results in a short stature, however normal sized head and torso (long bones can’t lengthen properly)
Outline the 2 types of osteoporosis (plus subtypes of the first one)
Primary osteoporosis:
1. Type 1:
In post-menopausal women
Due to an increase in osteoclast number
- Type 2:
In much older men and women
Due to a loss of osteoblast function (senile osteoporosis)
Secondary osteoporosis:
Result of drug therapy
