WEEK 8 - CONNECTIVE TISSUES Flashcards
CONNECTIVE TISSUES
what is connective tissue?
- wherever there is a space would be filled with connective tissue
- it comes from embryo – the mesenchyme that comes from stem cells in the mesoderm which is found between the ectoderm and endoderm in the embryo
- can differentiate into cartilage, adipose tissue, connective tissue and bone
- connective tissue has important roles such as:
- gives us a structural framework
- help us transport fluids and dissolve materials
- help protect delicate organs
- support and surround and interconnect tissues
- used for storing energy reserves
- defending body from microorganisms
extra-cellular matrix ECM
ECM - a 3D network of proteins and other molecules that surrounds and supports cells and tissues in the body
Composed of:
* Collagen fibrils - strength
* Elastic fibres - stretch
* Ground substance (jelly like material) - Mechanical support, holds water, cushioning
* Adhesion proteins - Links between cells & ECM
* Basal laminae (basement membrane) - Sheet, underlies/surrounds (many) cell type
ECM - collagen fibers
- 42 collagen genes
- long stiff triple stranded helix
- Major component of skin and bone
- Most abundant protein in mammals
- ~25% of total protein mass
- Type I most abundant, specialised Type IV –only found in basement membranes
- Structure –3 α-chains form a triple stranded helix
- Every 3rdAA in α-chain is glycine
- synthesis in the endoplasmic reticulum and are secreted by exocytosis
- intermolecular crosslinks → enables fibre formation and gives strength
- Collagen fibres form meshes
- Regular, tendons/ligaments collagen will run parallel
- Disorganised
ECM - elastin fibers
- Formed from elastin
- Cross-linking of individual monomers = stretchy fibre
- Function – enables organs to stretch and return to original shape
ECM –Ground substance (intercellular substance
- A mechanically supportive gel
- Allows diffusion of nutrients etc.
Comprised of :
* Glycosaminoglycan (GAG) chains
- Repeating disaccharides (sugar chain)
- Rigid – enables to fill space
- Polar, lots of -OH, can form lots of H bonds
- Example - hyaluronan
* Proteoglycans
- Protein core – highly glycosylated
- Contains one or more GAG
- Example - aggrecan (major proteoglycan of cartilage)
- Aggregates –assembly of GAGs and proteoglycans
- Viscosity vs rigidity dependent on assembly make-up
- Potential to be mineralised (bone) since can be very rigid if required
ECM - adhesion proteins
- Also termed cell adhesion molecules (CAMs)
- Link components of ECM together
- Link ECM to cells, e.g. Fibronectin (plays role in cell adhesion, migration, differentiation and very important in wound healing and embryonic development
- adhesion proteins can also be used to signal white blood cells to come out of the blood and into the tissue
ECM -Basement membrane (basal lamina)
- Flexible, tough, thin sheet of matrix molecules
- Laminin –primary structure (assembles into a 2D sheet)
- Type IV collagen – helps forms mesh, Interacts head to head/tail to tail
- Role :
- Selective barrier to cells, Semipermeable filter – e.g. kidney glomeruli
- Supports all epithelial cells, muscle cells and nerve cells outside of the CNS
- Scaffold for regeneration
connective tissue - cells
Key cells generating connective tissue :
* Fibroblasts
- Secret collagenous ECM throughout the body
-Migrate to damaged tissues, role in repair
- Ubiquitously distributed (found everywhere)
* Osteoblasts
- Secret bone ECM
* Chondrocytes
- Cartilage generators
- Secretory cells –prominent ER & golgi apparatus
- allows them to exocytose large proteins & proteoglycans for ECM
- all differentiate from same mesenchymal cell lineage
connectie tissue cells pt2
Key cells residing in connective tissue :
* Adipocytes
- Store fat
- White – few (or one) large fat droplets, nucleus and any other organelles pushed to side (used mainly for storage)
- Brown – many smaller fat droplets, multiple mitochondria (used mainly for creating and using energy)
- Differentiate from the same mesenchymal cell lineage as fibroblasts
* Immune cells
- Macrophages
- White blood cells, Patrol & remove micro-organisms
connective tissue - types
Types of connective tissue :
* Loose (areola) vs dense
* General
* Specialised
- Adipose
- Blood (lymph)
- Bone
- Cartilage
connective tissue - loose (areolar)
loose connective tissue
* elastic fibre (thin) , collagenous fibres (thick)
* has lots of space between fibres that will be filled by ground substance
- roles :
- Attachment – skin to underlying tissues
- Fills void around organs, Cushioning & protection, holds organs in place
- Supports & surrounds blood vessels
- Diffusion – nutrients, O2, due to abundant amount of ground substance
Structure :
* Fibres run in all directions –loose network
- Collagen –predominant fibre
- Elastic fibres –less prominent
* Ground substance
* Fibroblasts –lay down further fibres
* also contains :
- Adipocytes
- Blood vessels & lymphatics
- Inflammatory cells
- Patrolling macrophage
connective tissue - dense
- key role is to support other tissues
- found in tendons, bone, cartilage, ureter
- not same level of ground substance
- Characterisation :
- Abundant fibres & fewer cells vs loose
- Also termed –fibrous/collagenous connective tissue, due to vast abundance of collagen fibre
- Structure :
- Fibres in dense network, Parallel or irregular
- Little ground substance
- General, e.g. Tongue
- Specialised, e.g. Bone, Cartilage, Tendon
connective tissue - dense regular
- Ligaments & tendons
- Almost avascular (little to no vascular network due to how tight the collagen fibres will line up)
- Collagen fibres run parallel
- Contains fibroblasts, In rows between fibres and can secrete further fibres
- Roles :
- Attach bone to bone & muscle to bone
- Stabilise the join
Connective tissue – cartilage
- 2 growth mechanisms
- Appositional (where we add new layers of cartilage to the surface)
- Interstitial (where cartilage from within enlarges)
- Chondrocytes
- Form cartilage, Post ECM deposition become less active
- 2 main proteins
- Collagen (mainly type II) – mechanical stability
- GAGs – compressive forces
cartilage growth
interstitial
* growth from within
-interstitial growth diving of chondrocytes to produce daughter cells which will then start producing cartilage
*interstitial most important during growth
* key for development
appositional
* new layers of cartilage to surface
* cells in the inner layer will divide repeatedly
* will only occur post-development if there has been damaged
-production of chondroblasts (immature chondrocytes) which once embedded become chondrocytes themself.
Connective tissue –cartilage
3 types of cartilage :
* Fibrocartilage –resists compression & tension
-Type I & II collagen
-Vertebral disks, tendon attachments to bones & junctions between flat bones and pelvis
* Hyaline cartilage –flexible & resilient
-Type II collagen
-Temporary skeleton (foetus)
-Growing points –long bones
-Support tissue –respiratory passages
-Articular cartilage –synovial joints
* Elastic cartilage –highly bendable
-Elastic fibres & type II collagen
-Ear & epiglottis
Connective tissue -bone
- Growth & remodelling
-Osteoid –predominantly type I cartilage
-Bone –mineralised/calcified, Ca3(PO4)2, type I cartilage - Osteoblasts
-Found on surface of growing bone
-Secret matrix components
-Transform and differentiate to osteocytes –once enclosed in bone, Bone maintenance
Connective tissue -bone pt2
- Remodelling
- Osteoclasts –large multinucleated cells
-Bone resorption
-Suction cup
-Microvilli boarder -↑ surface area, H+ATPase & Cl-channels secrete HCl, Lysosomal proteases digest collagen
-Digestion products -transcytosed
Connective tissue -adipose
- Function
-Protection
-Insulation
-Nutrient storage - White adipose
-Stores fat –large droplets
-Found under skin & surrounding organs - Brown adipose
-Stores fat –small droplets
-Many mitochondria
-Burns fat –releasing energy -heat - White blood cells (leukocytes)
-T-helper cells activate:
-B-lymphocytes –antibody production
-Killer T-cells –kill virally infected cells - Neutrophils, basophils, eosinophils & macrophages
-Pass into wounds/connective tissue –seek out and destroy bacteria, tumour cells…. by phagocytosis and/or lysis
-Contain lots of lysosomes & lytic enzyme granules
what roles are played by the connective tissue?
- support
- storage of energy supplies
-protection
Which of these description best fits the collagen fibres?
A triple helix of fibrous collagen protein
Which amino acid is found at every third position in collagen?
glycine
The most common form of collagen found in the basement membrane is
type IV
What are the major materials packed around the collagen fibres in the extracellular matrix?
Glycosaminoglycans
What protein are the stretchy fibres of the connective tissue made from?
elastin
The type of tissue that contains a fluid known as the “ground substance” is:
connective/support
What function do the various components of the ECM play?
- Elastic fibres
- return to original shape after distorting - Collagen fibres
-strength - Glycosaminoglycans (GAGs)
-support
-water retention - Adhesion proteins
-link cells to ECM
-link components of ECM together
Name three types of cell found in the connective tissue
osteoclast, fibroblast, osteoblast, osteocyte, chondroblast, chondrocyte, adipocyte, macrophage, white blood cell
Where would you find loose and dense connective tissue?
loose - tongue
dense - tendons
Name the two process by which cartilage grows
Appositional, Interstitial
What type of cartilage would you find in the following locations?
- Fibrocartilage
- vertebral discs
- tendon attachment to bone - Hyaline cartilage
- skeleton in developing foetus
- growing point of long bones - Elastic cartilage
- epiglottis
- ear
What functions do the following cells / materials play in bone?
- Bone reabsorption
- osteoclast - Cells at growing surface secreting ECM
- osteoblast - Cells within bone ECM; bone maintenance
- osteocyte - Extracellular matrix of bone
- osteoid
what is involved in bone reabsorption?
- transcytosis
- secretion of lysosomal enzymes
- secretion of acids
Osteoclasts secrete acid into the region of bone to be reabsorbed, both to make the conditions required for lysosomal (acid) hydrolases to work and also to solubilise calcium phosphate from the bone ECM. Digestion products are then carried across the cell by transcytosis to be release on the other surface.
The blood cells are derived from:
mesenchyme
Blood consists of two components. The fluid stroma or plasma consists mainly of
water
