Week 1 - Connective tissue and Cartilage Flashcards
Definition of tissue?
A group of cells that usually have a common embryonic origin and function together to carry out specialised activities.
What factors are the structure and properties of a specific tissue influenced by?
→ Nature of extracellular matrix
→ Connections between cells that compose the tissues
What form may tissues in the body take?
Hard (bone)
Semisolid (fat)
Liquid (blood)
What are the 4 principal types of tissue in the body?
Epithelial (skin)
Connective
Muscular
Nervous
Role of epithelial tissue?
→ covers body surface
→ lines hollow organs, body cavities, ducts
→ forms glands
→ first line of defence against pathogens
Examples of connective tissue?
skeletal tissue, cartilage, bone, blood, fat etc
Role of muscular tissue?
→ cells specialised for contraction/generating force
→ generating body heat
Role of nervous tissue?
→ detects change in a variety of conditions
→ responds by generating electrical signals - action potentials that activate muscular contractions and glandular secretions
What are the functions of connective tissue?
- binds together, supports + strengthens other body tissues
- protect and insulate internal organs
- major transport system - blood
- store energy reserves - adipose
- main source of immune response - platelets/lymph
What are the 2 basic elements of connective tissue?
Cells
Extracelular matrix
What is the extracellular matrix?
Material located between the widely spaced cells
What does the extracellular matrix consists of?
→ protein fibres
→ ground substance (material between cells and fibres)
How is extracellular matrix formed?
Cells usually secrete ECM components and create environment in which they are living.
The type of connective tissue secreted by cells determines tissue type.
e.g.
Cartilage → ECM - firm but pliable
Bone → hard and inflexible (calcified)
Examples of immature connective tissue cells and role?
blast = bud or sprout
e.g.
fibroblasts → loose and dense connective tissue
chondroblasts → cartilage
osteoblasts → bone
Retain the capacity for cell division and secrete the extracellular matrix
What do resident cells do?
They stay where they are made and never move.
What do fluctuating cells do?
Move around body in order to get to specific areas depending on their function.
Key note about resident and fluctuating cells?
Some cells e.g. macrophages can be resident and fluctuating but cells normally fall into either or category.
When do immature connective tissue cells mature?
Once cells have finished producing the extracellular matrix and have done all the cell division needed.
They begin to differentiate.
What is the mature cell suffix?
Cyte
What is the role of mature cells?
Reduction in capacity for cell division and extracellular matrix.
Mostly involved with maintaining the matrix (look after it rather than create it).
What are the 6 types of connective tissue cell types?
(vary according to type of tissue as cell produces ECM + fibres and that determines tissue type)
- Fibroblasts → connective tissue
- Adipocytes/Lipocytes → fatty tissue
- Macrophages → immunity
- Lymphocytes → immunity
- Mast cells
- Plasma cells
What are the resident connective tissue cell types?
Fibroblasts → present in general connective tissue, most numerous
Adipocytes/Lipocytes
What are the fluctuating connective tissue cell types?
Macrophages
Lymphocytes
Mast cells
Plasma cells
What do fibroblasts do?
Secrete extracellular matrix e.g. collagen, active during wound repair - forms granulation tissue.
What do adipocytes/lipocytes do?
Store and synthesise fats
What do macrophages do?
Engulf and digest bacteria or foreign bodies (Phagocytosis)
May be resident or fluctuating
What do lymphocytes do?
Involved in defence mechanism, migrate to sites of parasitic invasions and allergic responses.
What do mast cells do?
Produce histamine (chemical mediator) through vasodilation.
Involved in defence mechanism.
What do plasma cells do?
Involved in defence mechanisms, secrete antibodies
What ways can the ground substance take form?
→ Fluid
→ Semifluid
→ Gelatinous
→ Calcified
What does ground substance contain?
- water
- complex combination of large organic molecules:
(such as)
→ complex combination of polysaccharides (glycosaminoglycans (GAGs))
→ proteins proteoglycans
What is the role of ground substance?
→ support cells, provides a medium through which substances are exchanged between the blood and cells
→ important for tissue development, migration, proliferation, changing of shape and metabolism
→ acts as a mechanical barrier
→ adhesion proteins present, main one = fibronectin, which binds collagen fibres and ground substance
What are the 3 fibre types embedded in the extracellular matrix?
- Collagen
- Elastic
- Reticular
Collagen key information?
(Colla = glue)
→ very strong, resist pulling forces, allow flexibility
→ many diff. types - attracts more water than bone giving cartilage a cushioning effect
→ occurs in parallel bundles
→ orientation of fibres depends on stresses/direction of force
Elastic key information?
→ smaller diameter than collagen
→ branch/join together forming a network
→ made up of protein molecule elastin surrounded by a glycoprotein named fibrillin
→ strong - can be stretched up to 150% of relaxed strength
→ able to return to original shape (elasticity)
Reticular key information?
(Reticul=net)
→ consists of collagen arranged in fine branching bundles
→ coated in glycoprotein
→ support blood vessel walls and forms network around cells for some tissues e.g. breast, adipose + smooth muscle
→ produced by fibroblasts
→ common in reticular connective tissue - forms supporting framework of many soft tissue organs
Where is collagen mainly found?
bone, cartilage tendons and ligaments
Where is elastic mainly found?
skin, blood vessel walls + lung tissue
Where is reticular mainly found?
many soft tissue organs such as the speed and lymph nodes
Key features of mature connective tissue?
→ present at birth
→ mesenchymal cells give rise to the cells of connective tissue
Types of mature connective tissue?
𝗖𝗼𝗻𝗻𝗲𝗰𝘁𝗶𝘃𝗲 𝘁𝗶𝘀𝘀𝘂𝗲 𝗽𝗿𝗼𝗽𝗲𝗿 → flexible, contains ground substance with abundant fibres
𝗦𝘂𝗽𝗽𝗼𝗿𝘁𝗶𝘃𝗲 𝗰𝗼𝗻𝗻𝗲𝗰𝘁𝗶𝘃𝗲 𝘁𝗶𝘀𝘀𝘂𝗲 → protects and supports soft tissues of the body
𝗟𝗶𝗾𝘂𝗶𝗱 𝗰𝗼𝗻𝗻𝗲𝗰𝘁𝗶𝘃𝗲 𝘁𝗶𝘀𝘀𝘂𝗲 → extracellular matrix is liquid
5 subtypes of mature connective tissue?
- Loose connective tissue
- Dense connective tissue
(connective tissue proper) - Cartilage
- Bone tissue
(supporting connective tissue) - Liquid connective tissue
Loose connective tissue key points?
→ more extracellular matrix
→ cells more interdispersed (here and there)
→ haphazard web-like structure of fibres
e.g. areolar connective tissue, adipose tissue, reticular connective tissue (in and around nearly every body structure)
Dense connective tissue key points?
→ high prop. collagen fibres (arranged in parallel orientation)
→ load/tensile strength increased as net load is distributed (semi)uniformly across range of fibres.
→ cells interdispersed between layers of protein fibres → more dense than loose CT
e.g. tendons/ligaments/aponeuroses, fasciae/periosteum/perichondrium, lung tissues/arteries
Bone tissue key points?
→ matrix type - calcified
e.g. compact and spongy bone tissue
Liquid connective tissue names?
e.g.
blood - within blood vessels
lymph - within lymph system
What are the components of cartilage?
Cells → Chondroblasts, fibroblasts, chondrocytes.
(chondroblasts produce ECM, chondrocytes maintain ECM)
Extracellular matrix → Gelatinous
Fibres → (predominant) = Collagen - lesser prop. of elastin and reticulan
How is connective tissue different to other tissues?
→ do not appear on body surfaces unlike epithelia
→ usually highly vascular except for cartilage (avascular) and tendons (lesser blood supply)
→ supplied with nerves (not cartilage)
→ large amount of extracellular material
→ cells usually widely scattered
How do the sub-types of mature connective tissue differ from each other?
→ Fibres of loose connective tissue = loosely arranged.
→ Dense connective tissue contains numerous thicker + denser fibres/ considerably less cells than loose CT.
→ Cartilage has a higher prop. collagen fibres with a gel-like component of the ground substance meaning it can endure more stress than others above.
→ Bone tissue = compact or spongy - extracellular matrix usually 25% water, 25% collagen fibres and 50% crystallised mineral salts (calcified extracellular matrix)
→ Liquid connective tissue has a liquid extracellular matrix
What is cartilage and what does it do?
Dense network of collagen fibres firmly embedded in chrondroitin sulfate.
→ can endure considerably more stress than loose and dense connective tissue
→ high resistance to tensile, compressive and shearing (rotational) forces
Cartilage has its strength due to: collagen fibres + chondroitin sulfate
What is chrondroitin sulfate?
A gel like component of the ground substance of cartilage.
Gives it resilience and elasticity.
Roles of cartilage?
- support soft tissues
- provide smooth, gliding surface for bone articulations at joints
- enable the development and growth of long bones
What is skeletal connective tissue considered as?
skeletal connective tissue
(specialised/supportive connective tissue)
Types of cartilage?
hyaline (articular cartilage)
fibrocartilage (articular cartilage)
elastic
Features of hyaline cartilage?
Collagen: Thin, fine collagen fibres
Location of cells: Prominent chondrocytes found in lacunae
Presence of perichondrium:
- Most hyaline cart. surrounded by perichondrium
- Not for articular cart. in joints + epiphyseal plates
Characteristics: Most abundant, provides flexibility + support, reduces friction + absorbs shock @ joints
Relative strength: weakest of 3
Features of fibrocartilage?
Collagen: Thicker bundles of collagen fibres
Location of cells: Chondrocytes scattered among thicker bundles of collagen fibres
Presence of perichondrium: Lacks perichondrium
Characteristics: Strong + rigid
Relative strength: Strongest of 3
Features of elastic cartilage?
Collagen: Threadlike network of elastic fibres within extracellular matrix
Location of cells: chondrocytes located within threadlike network of elastic fibres within ECM
Presence of perichondrium: Perichondrium present
Characteristics: Gives support and maintains shape
Relative strength: 2nd strongest
What is the perichondrium?
A dense layer of fibrous connective tissue that surrounds the perimeter of most cartilage surfaces.
Articular cartilage - e.g. fibrocartilage and some hyaline cartilage - is not covered by perichondrium.
(Whereas the periosteum is a thin layer of membranous connective tissue that covers all bones in the body).
Cartilage key points?
→ supporting/specialised connective tissue type
→ relatively asvascular- penetrated by vascular channels from surrounding tissues (perichondral blood vessels) - secretes antiangiogenesis
→ no nerve supply
→ during early embryonic life - skeleton is mostly cartilage, which is gradually replaced by bone
How may cells be arranged in cartilage?
Cells are either singular or in groups occupying small spaces called lacunae in the matrix, which conform to the cell shape.
How do type 2 and type 1 collagen differ?
Type 2 is hydrophilic whereas type one is not and is much more dense
How are the protein fibres arranged in cartilage?
Meshwork of collagen (mainly type 2 fibres) are embedded within the ground substance
Meshwork arrangement of collagen gives strength and helps to hold gel-like ground substance in place.
How is the ground substance arranged in cartilage?
→ firm gel allows for diffusion of nutrients
→ 60-90% = water, lipids, electrolytes and complex macromolecular protein - proteoglycan
What is proteoglycan?
- found within ground substance
- complex macromolecules = core protein attached to Glycosaminoglycans (GAG’s)
- Proteoglycans bind with water = ‘molecular sponge’, allows compressibility and shock absorbency
-Proteoglycans+ Water are held in position by the meshwork of collagen fibres, allowing cartilage to be compressible
What is fibronectin?
The protein responsible for binding structures to the cell body
What happens to articular cartilage in the onloading phase?
Fluid pressure rises immediately
Cartilage gradually deforms
Water moves out
What happens to articular cartilage after the removal of load?
Fluid pressure drops
Cartilage gradually returns to normal shape
Water moves back in
How do the collagen arrangements in different layers of articular cartilage differ?
Superficial tangential (10-20%) - roughly parallel with articular surface membrane
Middle (40-60%) - arches or ‘collagen arcade’
Deep (30%) - vertical orientations of collagen fibres
What is the tide mark in cartilage?
Between a component of calcified cartilage and and the deep cartilage which is vertical
What is the subchondral bone?
The layer of bone underneath the cartilage
How does articular cartilage receive nutrition?
By diffusion from:
→ underlying subchondral bone
→ synovial membrane at periphery of the cartilage
→synovial fluid in the joint
What 2 layers does the perichondrium consist of?
- 𝗢𝘂𝘁𝗲𝗿 𝗹𝗮𝘆𝗲𝗿: contains blood vessels and fibroblasts (which produce collagen). Can change into fibrocytes which will maintain environment (ECM).
- 𝗜𝗻𝗻𝗲𝗿 𝗹𝗮𝘆𝗲𝗿: contains undifferentiated cells i.e. Stem cells which can develop into chondroblasts, important in growth and repair
Why is it important to have these stem cells in the perichondrium?
→ cartilage is a relatively inactive tissue that grows slowly
→ cartilage has a low ability to regenerate and probably only does so in the young (given its avascular nature)
→ in adults damage to cartilage results in formation of fibrous scar tissue - which does not have the same properties as hyaline cartilage.
2 ways cartilage can grow? (in respect to repair)
- 𝗜𝗻𝘁𝗲𝗿𝘀𝘁𝗶𝘁𝗶𝗮𝗹 𝗴𝗿𝗼𝘄𝘁𝗵: occurs when the cartilage is young and pliable during childhood and adolescence.
- 𝗔𝗽𝗽𝗼𝘀𝗶𝘁𝗶𝗼𝗻𝗮𝗹 𝗴𝗿𝗼𝘄𝘁𝗵: starts later than interstitial growth and continues through adolescence.
How does interstitial growth occur?
Rapid size increase due to the division of chondrocytes and continuous deposition of ECM.
Expands like rising bread as chondrocytes are pushed away from each other as they synthesis the new matrix.
How does appositional growth occur?
Growth on the outer surface of the tissue.
- Cells in the inner cellular layer of the perichondrium differentiate into chondroblasts.
- Differentiated cells surround themselves with ECM and become chondrocytes.
- Matrix accumulates between perichondrium on the outer surface of the cartilage causing it to increase width.
