12 - Cartilage and Bone Flashcards
What is cartilage?
Avascular connective tissue that consists of chrondocytes and a semisolid extracellular matrix
What are the three types of cartilage and what are their extracellular matrixes made of?
All matrix have proteoglycan and hyaluronic acid
- Hyaline: Type II Collagen aggregates to 100 hyaluronate proteoglycan
- Elastic: Elastic fibres and elastic lamellar
- Fibrocartilage (Fibrous): Mainly Type I collagen
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Where is hyaline cartilage found?
- Trachea
- Layrnx
- Articular at joints
- Nose
- Costal cartilage
- Epiphyseal growth plates
- Foetus
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What is the structure and function of hyaline cartilage?
Structure:
- Avascular
- Perichondrium on edges.
- Perichondrocytes differentiate into chondroblasts then chondrocytes, which sit in lacuna.
- Isogenous groups.
- Chondrocytes separate as they release extracellular matrix.
Function:
- Xcell matrix is full of water. Water non-compressible so resilient to increased loads.
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What is the function of cartilage?
- Resilient
- Firm
- Flexible
- Strength
Fibres, Water and Ground substance make up xcellular matrix that give cartilage it’s properties. Allows Articular joints to slide over each other
How does cartilage get nutrients?
Cartilage avascular. Nutrients have to diffuse from vessels in the perichondrium to the extracellular matrix.
What is a proteoglycan?
Make up ground substance. Core protein with GAG covalently bound.
What is GAG?
Glycosaminoglycans. Long chained poly-saccharides. They attract water to form hydrated gel that permits rapid diffusion but resists compression
What GAG is predominantly found in cartilage?
Hyaluronate. Binds to core protein to form proteoglycan that is massively hydrophilic, attracts water to form gel.
Why is the extracellular matrix of cartilage more gel-like than other connective tissues?
Contains more proteoglycan so in ground substance
What cartilage is present in the trachea and why?
Hyaline (below submucosa). Reinforces trachea to protect and maintain airway
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When does cartilage repair itself?
It doesn’t, chondrocytes cannot divide. Fibroblasts replace cartilage with fibrous scar tissue
Where is elastic cartilage found?
- Pinna of ear
- Eustachian tube (inner ear to oral)
- Epiglottis
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What is the function of the elastic cartilage?
Areas that need extra flexibility and support
What is the structure of elastic cartilage?
Perichondrium containing fibroblasts. Lots of chondrocytes surrounded by dense elastin fibres. ‘Gaps’ where chondrocytes have laid down their elastic and died.
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Where is fibrocartilage found?
- Pubic symphysis
- Intervertebral disc
- Knee menisci (padlike cartilage)
- Articular joint of sterniclavicular and temporomandibular
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What is the function of fibrocartilage?
Found in areas of directional stress, so shock absorbs and resists shearing forces.
What is the structure of fibrocartilage?
- Few chondrocytes and few fibroblasts arranged in rows, in collagen. No surrounding perichondrium.
- Mix of hyaline cartilage and dense regular connective tissue
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What two tissues can fibrocartilage be called a mixture of?
Hyaline cartilage and dense regular
How do bones develop in the fetus in simple terms?
Hyaline cartilage model mineralises to form bone and then grows by endochondral ossification
What cartilage is at bone ends?
Hyaline Articular with no perichondrium. Nutrients come from synovial fluid.
Is bone inert?
No it is dynamic, constantly being broken down and remodelled
What is compact bone made of?
Concentrically arranged lamella. Osteons.
What is cancellous bones made up of?
Trabeculae. Lamellae woven together
Which bones have a greater proportion of spongy bone?
Short
What is appositional bone growth?
- Bone remodelling
- Growth in width
- Bone taken from endosteum and added to periosteum
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What is interstitial growth?
- Growth from the centre.
- Increase in bone length.
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What is the periosteum?
Dense irregular connective tissue, connected to the outside of bone by collagen fibres called Sharpey fibres.
- 1st layer - dense collagenous with nerves, fibroblasts and vessels
- 2nd layer - Osteogenic cells, less vascular
CONTAINS NERVES, LYMPH AND BLOOD VESSELS
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What is perichondrium?
Dense irregular connective tissue covering hyaline and elastic cartilage. It is vascular and supplies the cartilage chondrocytes with nutrients. Contains chrondroblasts
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What is the endosteum?
Thin connective tissue layer that lines marrow cavity. Dense irregular. Contains osteopregenitor cells
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Where is the periosteum present?
Covering every bone, bar the patella and phalanges, and disappears at articular surfaces
What is the structure of compact bone?
- Osteons run parallel to long axis
- Haversian canal at the middle (containing lymph, vessels, nerve), surrounded by concentric lamellae
- Lacuna in osteon containing osteocytes. Form canniculi with one another and haversian for nutrients
- Haversion’s and spongy bone joined by Volkmann’s canal
- Collagen in each lacuna run in different directions for high torsion strength
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What is an:
- Osteoblast
- Osteocyte
- Osteoclast ?
Osteoblast: Intermediate cell on endosteum that cannot divide. Lays down osteoid
Osteoclast: Large WBC on endosteum that undergoes resorption of bone, remodelling it. Not in bone itself
Osteocyte: Terminally differentiated cell when osteoblast trapped in osteoid. No longer lays down matrix just maintains tissue.
Osteogenic Cell —> Osteoblast —> Osteocyte
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What are the inorganic and organic components of bone matrix and their function?
Inorganic - 65%.
Calcium, Phosphate, Mg and Al Salts
Resist bending and compressing
Organic - 35%.
Collagen 1, GAGs, proteins like osteocalcin and osteonectin.
Resist pulling and tension forces
What is osteoarthiritis?
- Age related degeneration
- Degeneration of articular cartilage so narrowing of joint space, bone rubs against bone
- Growth of bony spurs, osteophytes, that cause inflammation and pain
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What is rheumatoid arthiritis?
- Autoimmune disease
- Inflammation of synovial membrane, thickening joint capsule
- Damage to underlying bone and articular cartilage so both degenerate
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What does a synovial joint look like with rheumatoid arthiritis?
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