connective tissue adaptation Flashcards
What are the 4 tissue types?
- epithelial
- connective tissue
- nervous tissue
- muscle
What is connective tissue made up of?
- relatively few cells
- mostly made up of ECM (proteins such as elastin and collagen, ground substance)
How is ECM formed?
- formed by the cells of the connective tissue
- which secrete macromolecules in the ECM
- components vary between different connective tissues
What does ECM do?
- separates and holds the cells in place
- maintains tissue and cell integrity
- mediate the exchange of nutrients and waste
- transmits chemical signals to the cells to regulate migration, growth, differentiation
Describe the structure of collagen fibres
- composed of protein collagen
- triple helix of polypeptide chains
- hierarchal structure ( microfibril, fibril, fibre)
- great tensile strength
- compliant due to arrangement of fibrils and crimp
- 29 forms, five common sub-types found in different areas of the body
Describe the structure of elastic fibres?
- composed of the protein elastin
- coiled structure
- cross-links between molecules
- ability to stretch
What is ground substance?
- gel-like material
- transparent
- fills spaces between cells and fibres
What is ground substance made up of?
- made of large molecules called glycosaminoglycans (GAGS)
- GAGS linked via proteins into even larger proteoglycans
- hydrophilic (90% is water)
- high water content and inflexible molecules mean very good at resting compressive forces
What cells does the ECM contain?
- fibroblasts
- adipocytes
- immune cells
- other specialised cells e.g.. osteocytes and blasts, chondrocytes and blasts
What are fibroblasts?
- least specialised cells, secrete collagen and ground substance
What are adipocytes?
- fat cells
Name immune cells found in ECM?
- macrophages
- mast cells
- plasma cells
What is a tendon?
- A type of fibrous connective tissue (dense regular connective tissue)
- comprised of collagen fibres tightly packed and running in the same direction
- excellent tensile strength in one direction
What are the components of a tendon?
- cells such as tenocytes (specialised fibroblast)
- fibres, predominantly collagen type 1 and a small amount of elastin
- ground substance ( proteoglycans and water)
What is a ligament?
- Dense regular connective tissue
What is the structure of a ligament?
- similar to a tendon
- slightly less ground substance
- fibrils not as uniformly orientated to cope with multiaxial loading patterns
What is cartilage?
- A specialised type of connective tissue
- three types of cartilage
What are the general components of cartilage?
- cells, chondrocytes (chondroblasts that get trapped)
- fibres - collagen type 2
- ground substance - proteoglycan aggrecan (10%) takes up lots of water (75%)
- composed of GAGS (hyaluronic acid, chondroitin sulphate, keratin sulphate)
What is a hyaluronic acid/hyaluronan?
- very large GAG molecule
- very hydrophilic
- increases tissue viscosity when bound
- excellent lubricative properties
- important in tissue repair (linked to tumour progression)
What is chondroitin sulphate and keratin sulphate?
- highly charged sulphate groups repel (anti-compression)
- link up with proteins to form proteoglycans (e.g. aggrecan)
What is hyaline cartilage?
- most common kind of cartilage
- glassy appearance
- specialised by collagen type 11
- weakest type of cartilage
Where is fibrocartilage found?
- found if certain regions of the body undergoing tension as well as compression
- e.g., intervertebral disc, joint capsules, ends of ligaments
How is fibrocartilage specialised?
- abundant collagen bundles sandwiched in between cartilage layers
- strongest type of cartilage
Where is elastic cartilage found?
- areas that need to be flexible but return to a certain shape
- e.g. pinna ( external part of ear) , epiglottis (tissue beneath tongue) , larynx
How is elastic cartilage specialsed?
- many elastin fibres
- strong and flexible
Describe the ECM in hyaline cartilage at articular surfaces?
- surface has tight collagen sheets parallel to to surface
- middle zone has random and less dense arrangement to accommodate proteoglycans and water
- deep zone has radial fibres that penetrate into calcified cartilage and bone to anchor the cartilage
- chondrocytes also have different shape and distribution
What is bone?
- A specialised type of connective tissue
What are the components of bone?
- cells - osteoblasts, osteocytes, osteoclasts
- fibres - predominantly collagen type 1
- ground substance - inorganic hydroxyapatite (calcium phosphate crystals)
- organic GAGs
Forces and movements are applied to locomotory structures - what do they produce?
- compression
- shear
- tension
- bending
- torsion
What is tissue stiffness?
- how much the tissue deforms when loaded
What happens if continual stress is applied to a tissue?
- There is a move from elastic region to plastic region (permanent deformation)
- e.g., microfractures, tears and eventual failure (breaking)
Describe a brittle material
- will not deform/ change length
- doesn’t absorb much energy before failing
- high failure strength
Describe ridge and tough materials
- deform a bit
- absorb quite a lot of energy
Describe compliant materials
- deform a lot under relatively low loads
How does the ECM respond to loading?
- ECM transmits force to cells
- cells surface receptors activate intracellular signalling pathways
- there is a continuous ECM turnover by cells
(secrete enzymes to break down ECM)
(secrete components of ECM) - cells increase matrix turnover in response to load
What is Wolff’s law?
- bone is laid down where needed and reabsorbed where not needed
Remodelling of bone is regulated by what stresses and strains?
- magnitude
- frequency
- rate
- loading cycles
- distribution
What does exercise lead to in tendons?
- increased number of fibroblasts
- increased collagen synthesis
- increased tendon cross-section
What does exercise lead to in cartilage?
- increased size and number of chondrocytes
- increased ECM
what does disuse of cartilage lead to?
- reduced proteoglycan synthesis
What does excessive loading of cartilage lead to?
- synthesis rate decreases
- degradation rate increases
