ECM & CELLS Flashcards
(28 cards)
What does ECM stand for?
extracellular matrix
Elaborate on the ECM found in bone
. Collagen = gives tensile strength
Experimental evidence =when bone is heated to denature collagen ( a protein) bone is easily fractured / shattered
- At different angles in different lamellae to increase strength
- In osteons, they are arranged in concentric circles for strength & support
TBC
Elaborate on the ECM found in bone
continued….
. Calcium hydroxyapatite is interspersed in the collagen fibres
- they are different calcium salts
- they give compressive strength to the bone - when bone is demineralised by acid, bone = becomes flexible
. Proteoglycans are also present (proteins associated with GAGs)
Cells present in bones:
- Osteoblasts
Osteoblasts:
Synthesis, deposition and mineralisation of bone matrix
Lots of cytoskeletal proteins for stabilising cell shape and cell movement
Extracellular extensions for connecting to other osteoblasts- e.g., forming parallel collagen fibres
Cover the surface of growing or remodelling bone
Secrete ECM glycoproteins:
Osteocalcin is a local regulatory protein
Regulates bone development and ossification
CBFA (core binding factor alpha 1) promotes differentiation of osteoprogenitor cells to osteoblasts- shown by knockout mice
Osteonectin:
Binds calcium hydroxyapatite to collagen
Osteopontin:
RGD sequences (integrins) which bind osteoclasts
Bone morphogenic protein:
Induce new cartilage and bone formation
Osteocytes
Osteocytes:
Form bone by controlling immediate area of bone tissue formation
Found in lacunae- mature version of osteoblasts- can no longer divide
Osteoclasts:
Multinucleate macrophages formed from blood-born monocyte precursors
Activated by osteoclast differentiation factor (RANK ligand) secreted by osteoblasts
Osteoprotegerin (OPG) produced by osteoblasts inhibits RANK ligand action by acting as a decoy receptor- inhibits bone break down
Balance between OPG and RANKL determines bone turnover
They attach by integrins to RGD sequences in osteopontin which seals osteoclasts onto bone
They face Howship’s lacunae (gives a ruffled edge to bone) and secrete acid and proteases to digest bone
Secrete hydrogen ions using protein pumps to break down calcium hydroxyapatites and proteases break down collagen
Name the cells found in soft connective tissue
fibroblasts, macrophages, mast cells, lymphocytes, adipocytes
Elaborate - Adipocytes
Adipocytes:
Triglyceride storage in white adipose tissue
Act as an energy store with the single, large lipid droplet
Formed from fusion of multiple lipid droplets in a cell
lymphocyes - 1 sentence
Lymphocytes are white blood cells derived from bone marrow and travel in the blood to reach the lymph
Mast cells - explain
Mast cells:
Secretory granules filled with bioactive molecules (like histamine, serotonin, etc.)
Activation of immunoglobulin E receptors on cells- activates mast cells and causes release of mast cell granules
They phagocytose bacteria- release granules, cause vasodilation, increase capillary permeability, break down ECM, contract smooth muscle (inflammatory response)
Macrophages - explain
Phagocytosis- engulf dead cells, invading organisms
Initiate and downregulate inflammatory responses
Recruit polymorphonuclear leukocytes to kill pathogens
They do degeneration of the ECM
Fibroblasts: - more
Cells elongated along the line of the fibres they secrete
These cells lay down collagen fibres in a particular orientation
Also secrete elastin, GAGs, proteoglycans, glycoproteins- they synthesise the ECM
Name the molecules which make up the ECM
- Collagen
- Elastin
- Glycosaminoglycan
- Glycoproteins
The molecules in the ECM are more plentiful than the cells that form it so determine the physical tissue properties
COLLAGEN
String of repeated glycine X Y (X is normally proline, Y is normally hydroxyproline)
3 collagen chains self-assemble into a right-handed triple helix
ELASTIN
Strongly crosslinked elastin core- creates a 3D structure surrounded by fibrillin-rich microfibrils
Elastin can stretch and recoil
It is covalently crosslinked to form fibres and/or sheets
Glycosaminoglycans (GAGs):
Long, unbranched polysaccharide chains
They are anionic so attract water and sodium to create the gel-like matrix- forms a highly hydrated gel-like ‘ground substance’ of the ECM
often are covalently linked to proteins to form proteoglycans
The gel formed can have varying pore size which determines the permeability of the ECM to molecules of different sizes
Resistant to mechanical pressure and acts as a lubricant
Glycoproteins:
Binding sites for matrix macromolecules and cells to bind onto the matrix
Can provide tracks on which cells can move within the matrix- guide cell movements
Tendons - Elaborate in detail
Tough bands of fibrous connective tissue (dense regular connective tissue)
The collagen fibres (mainly type 1 collagen) combine to form fascicles which are surrounded by endotendon- a sheath of connective tissue
Epitendon sheaths the entire tendon unit (also connective tissue)
Paratendon allows the tendon to move against neighbouring tissues
Tenoblasts are immature tendon cells which occur in clusters without collagen fibres, they proliferate a lot and synthesise collagen
Tenocytes are mature tendon cells and are anchored to collagen fibres
Tendons are capable of withstanding tension and connect muscle to bone
Attached by collagenous fibres called sharpey fibres which continue into the bone matrix
Ligaments - Elaborate in detail
Tough fibrous band of connective tissue (dense, fibrous bundles of collagen fibres)
Very little of the ground substance/ gel-like component of the tissue
Have fibrocytes which are spindle-shaped cells
White ligaments have lots of collagen fibres so are sturdy and inelastic
Yellow ligaments have lots of elastic fibres and are tough but allow elastic movement
Ligaments support internal organs
They hold bones together at joints for proper articulation
Form capsular sac that encloses articulating ends of bones and the synovial fluid
Fasten around bone ends to allow specific movements
Help prevent inappropriate movements, for example, at wrist and elbow joints
Aponeuroses - Elaborate in detail
Flat sheet/ ribbon-like structure of tendon-like tissue
They are elastically stretched when muscle contracts and recoil with muscle relaxation
They anchor muscles by connecting them with parts of muscles that move
Take the place of tendons in sheet-like muscle with a large area of attachment
Join muscles and the part of the body the muscle acts on, e.g. abdominal muscles
Fascia - elaborate in detail
Band or sheet of fibrous connective tissue
Mainly collagen arranged in a wavy pattern parallel to direction of pull
It is flexible, but also resists tension until the wavy pattern is flattened
It is beneath the skin and encloses and separates muscles and organs
Superficial fascia is in the subcutis and blends with the reticular layer of the dermis
Deep fascia is made of dense fibrous connective tissue and surrounds muscles, bones, nerves and blood vessels
Visceral fascia suspends organs in their cavities and creates layers of connective tissue membranes
Cartilage -
A hydrated matrix of proteoglycans and collagen (normally type 2 collagen)
Hydrated means the tissue swells until the limit of the fibres is reached which creates a good surface for distribution of loading
Cells of cartilage - name & elaborate
. Chondroblasts & chondrocytes
Chondroblasts are stem cells found in cartilage which are actively dividing
They synthesise the extracellular matrix
Form gap junctions with other cells- can be lost with interstitial growth
Have lots of ER, Golgi, vesicles, mitochondria because of their active role in the ECM
Chondroblasts mature and stop dividing which forms chondrocytes
These cells maintain the ECM in mature cartilage
They are more inactive as cells and have large lipid droplets
Chondrocytes end up embedded in a lacunae in the collagen matrix, limiting their dividing capabilities
Only a ….. ….. supply on the surface of the tissue so exchange occurs by …….- limits the size of cartilage as ……. is a limiting source of exchange
limited vascular
diffusion
diffusion
