BL S11 Bone And Cartilage Flashcards
What is cartilage?
An avascular tissue with an extensive extracellular matrix in which lie chondrocytes.
What do chondrocytes do?
They produce and maintain the extracellular matrix.
How do nutrients etc get to the chondrocytes if it is avascular?
The matrix permits ready diffusion of substances.
Describe the extracellular matrix of cartilage.
Proteoglycans, hyaluronic acid and type II collagen.
Hyaluronic acid + many proteoglycan linked together form hyaluronate proteoglycan aggregates.
High density of negative charge attracts water and forms a hydrated gel.
What are the 3 types of cartilage?
Hyaline
Elastic cartilage
Fibrocartilage
What are the differences in structure between the 3 types of cartilage?
Hyaline = proteoglycans + hyaluronic acid + type II collagen. Elastic = with elastic fibres added Fibrocartilage = type I collagen
What cells are in hyaline cartilage?
Chondrocytes only
How can chondrocytes within cartilage be present?
Singly or in isogenous groups
In an adult where is hyaline cartilage found?
Articulating surfaces Parts of ribs Trachea Bronchi Larynx Nose
In younger children where is hyaline cartilage found in addition to where it is found in adults?
Epiphyseal growth plates.
Perichondrium lines the margin of the hyaline cartilage.
What is it made of?
Dense connective tissue
Contains elongated fibroblast-like cells.
What will the elongated fibroblast-like cells develop into?
Chondroblasts and eventually chondrocytes.
What type of growth does do elongated fibroblast-like cells within the perichondrium give rise to?
Describe briefly this type of growth.
Appositional growth
Accomplished by addition of new layers on top of previously formed ones from the periphery of the cartilage.
What is interstitial growth?
Chondrocytes deeper in the cartilage may divide and separate as they lay down matrix.
What characteristics of cartilage confer it’s resilience to varying pressure loads?
The fact that it is a hydrated gel and the fact that water can move within the matrix.
Chondrocytes lie in __________.
Lacunae
What happens to hyaline cartilage for it to become bone?
Becomes mineralised.
Hyaline at articulating surfaces and in the epiphyseal growth plates has perichondrium.
True or false.
False.
Where is elastic cartilage found?
External ear (pinna)
External acoustic meatus
Epiglottis
Eustachian tube.
What cells are found in fibrocartilage?
Chondrocytes and fibroblasts.
Fibrocartilage is a combination of dense regular connective tissue and hyaline cartilage.
True or false?
True
Does fibrocartilage contain perichondrium?
No
Where is fibrocartilage found?
Intervertebral discs.
Articulating discs of sternoclavicular and temperomandibular joints
Knee joint menisci
Pubic symphysis
What is endochondral ossification?
The replacement of pre-existing template of hyaline cartilage by bones.
What type of bone develops this way?
Most long bones.
Describe what happens in terms of long bone growth at 6-8weeks (embryo) stage.
Periosteal bone will appear in shaft via intramembranous ossification - called bone collar synthesised by osteoblasts.
Describe what happens in terms of long bone growth at 5-6 weeks (embryo) stage.
Will be a hyaline cartilage template present .
Describe what happens in terms of long bone growth at the 8-12weeks (fetus) stage.
Central cartilage will calcify and a nutrient artery will penetrate supplying osteogenic cells.
This area is called the primary ossification centre.
Describe what happens in terms of long bone growth at the postnatal stage.
Medulla becomes cancellous bone.
Cartilage forms epiphyseal growth plates.
Epiphytes develop secondary ossification centres.
Describe what happens in terms of long bone growth at the mature adult stage.
Epiphyses - ossify - growth plates continue to move apart lengthening the bone.
Epiphyseal plates replaced by bone.
Articulating hyaline cartilage will persist.
In an LS of an epiphyseal plate, what is happening in the zone of reserve cartilage?
No cellular proliferation or matrix production.
In an LS of an epiphyseal plate, what is happening in the zone of proliferation?
Cells divide - form columns - enlarge and secrete matrix
In an LS of an epiphyseal plate, what is happening in the zone of hypertrophy?
Cells greatly enlarge
Matrix gets compressed in between columns of cells.
When enlarged they make enzyme alkaline phosphatase - promotes the calcification of matrix.
In an LS of an epiphyseal plate, what occurs in the zone of calcified cartilage?
Enlarged cells begin to degenerate
Matrix here is calcified.
In an LS of an epiphyseal plate, what occurs in the zone of resorption?
Calcified matrix is in direct contact with marrow cavity.
Small blood vessels and connective tissue invade the region occupied by dying chondrocytes leaving calcified cartilage as spicules between them
Bone is layer down on these spicules.
What is a synovial joint?
A moveable join in which the opposed bone ends are:
- Covered by hyaline cartilage
- Lie in synovial fluid bounded by an articular capsule.
What comprimises the articular capsule?
Synovial membrane
Fibrous capsule
What is the role of the synovial membrane?
Contains fibroblast-like cells that produce synovial fluid - lubricate
Macrophages - remove debris from joint cavity.
What is the role of the fibrous capsule?
Reinforces the joint cavity and synovial joint.
The fibrous capsule runs continuously with the periosteum.
True or false?
True.
What is osteoarthritis?
Degeneration and mechanical failure of articular cartilage.
Leads to narrowing of joint space and bone rubs against bone.
Growth of bony spurs called osteophytes cause inflammation and pain.
What is Rheumatoid arthiritis?
Autoimmune inflammation of the synovial membrane.
Results in thickening of the joint capsule.
Subsequent damage to underlying bone and cartilage occurs.
What is intramembranous ossification?
Bone growth that takes place within condensations of mesenchymal tissue and not via replacement of pre-existing hyaline cartilage.
Name some bones that develop via intrammemrabanous ossification.
Skull- parietal, frontal, temporal, occipital, maxilla and mandible.
Clavicle - lateral end
Scapula - mainly
Pelvic bones
Intramembranous ossification contributes to the ________ of long bones.
thickening
Describe the process of intramembranous ossification.
Cluster of mesenchymal stem cell - cluster - Indus
Become osteoprgenitor cells - more Golgi and ER
Become osteoblasts - lay down osteoid - ECM contain type I collagen.
Osteoid mineralises - bone spicules form
Osteoblasts and osteoclasts lay down bone on spicules which join to form trabeculae - merge to form woven bone which will be replaced by mature compact bone.
Woven bone is a form of _______ bone?
Immature
Is mesenchymal tissue vascularised?
Yes.
When an osteoblast becomes surrounded by the osteoid it has secreted it becomes an ________.
Osteocyte
What is osteoid?
Non-calcified bone
Trabecular bone is formed by _____ _________ growing and connecting together.
Bone spicules.
What is the difference between cancellous and cortical bone?
Cancellous bone forms a network of fine bony fibres with spaces in between filled with bone marrow whereas cortical bone forms the external surfaces of bones.
What percentage of body skeletal mass is compromised of cortical bone?
80%
What are 2 properties of cancellous bone?
Strong but light.
What is the difference between immature bone and mature bone?
Immature bone - osteocytes are randomly arranged whereas in mature bone they are arranged in concentric lamellae of osteons.
What’s the difference between haversian and Volkmanns canals?
Haversian canals run in the same axis and in the centre of osteon.
Volkmanns canals run transversely between the osteons connecting Haversian canal.
What do the harversian and Volkmanns canals carry?
Arterioles venules capillaries lymphatics and nerves.
How are nutrients transferred to and between the osteocytes within the lamellae?
Osteocytes have slender cytoplasmic processes that reach out to from gap junctions with other cells to allow for nutrient transfer.
Cytoplasmic processes lie within canaliculi which are though to connect with the central Haversian canal.
Why are there no haversian or volksmanns canals in cancellous bone?
Don’t need nutrients from the vessels that would normally be within the canals they can derived all the needed nutrients from the bone marrow.
What does each trabeculum consist of?
Osteocytes embedded within irregular lamellae of the bone.
What is found on the surface of the trabeculae?
Osteoblasts and osteoclasts which remodel the bone.
Interconnect trabeculae form bone cavities, what lies within these cavities?
Bone marrow
Adipose
Haemopoetic cells.
How does cortical bone remodel?
Osteoclatic tunnelling.
What are the steps in osteoclatic tunnelling?
Osteoclatic resorption
Layering of osteoblast
Layering of lamellae
Laying down a cement line
What cells make up the head of the cutting cone?
Osteoclasts.
What follows behind the osteoclasts in a cutting cone?
Capillaries and then osteoblasts which lay down osteoid to fill the cutting cone.
Cutting cones remodel through action of ______, _______ and ______.
Osteoclasts
Lysosomal enzymes
H+ ions.
Osteons ______ and __________ at different levels of bone.
Branch, terminate
What are some mechanical properties of bone?
High tensile strength
High compressive strength
Flexibility
What are the 4 stages of bone fractures repair?
- Haematoma - granulation tissue
- Fibrocartillaginous callus
- Bony callus
- Bone remodelling
What is a granulation tissue?
Is a connective tissue and microscopic blood vessels that ion the surface of a wound during the healing process.
In the haematoma formation step what removes the dead and damaged tissue?
Osteocytes and phagocytic cells.
In the haematoma formation step what removes the blood clot/ procallus?
Macrophages
In the procallus what do the fibroblasts make?
Collagen fibres.
What invades the fracture site in step 2 to begin forming trabecular bone?
Osteoblasts from periosteum and endosperm
Multipotent stem cells from bone marrow.
What is osteoporosis?
Osteoporosis is a metabolic bone disease in which mineralised bone is decreased to the point it no longer provides adequate mechanical support.
There are 2 types of primary osteoporosis, distinguish between them.
Type 1 occurs in post-menopausal women as a result of increased osteoclast number due to oestrogen withdrawal.
Type 2 occurs in elderly after age 70 due to decreased osteoblast function.
What are the main risk factors for osteoporosis?
- Genetic - blacks - higher bone mass
- Insufficient calcium intake
- Exercise - immobilisation of bone leads to to accelerated bone loss
- Cigarette smoking
Osteoporosis can alter _____ and _______.
Shape and posture.
Amongst whites, what do women have increased risk of.
Hip fracture and vertebral fractures.
How does osteoporosis with aging occur?
Incomplete filling of the osteoclast resorption bays due to decreased osteoblast activity.
What is osteomalacia?
Osteomalacia refers to softening of bones.
What is osteomalacia in kids called?
Rickets
How does osteomalacia occur?
Lack of vitamin D.
