POM 2 Flashcards
The difference between the extra cellular matrix, intracellular fluid, plasma, interstitial fluid and transcellular fluid please
Intracellular fluid is the fluid inside cells. Interstitial fluid is the fluid between cells. Plasma is the liquid part of blood. Transcellular fluid is fluid that’s not interstitial fluid or plasma or intracellular fluid and is made up of ocular fluid (fluid around the eyes), synovial fluid (fluid in joints) and CSF
Extracellular matrix
complex network of macromolecules (proteins + carbs) deposited by cells, which then becomes immobilised and fills spaces between cells
· Made of fibrillar and non-fibrillar components
Key functions
o Provide physical support
o Determine mechanical and physiochemical properties of tissue
o Influence growth, adhesion and differentiation status of cells and tissues w/which it interacts
Many varieties of ECM component exist:
o COLLAGENS
§ Type I (bone, skin and tendon)
§ Type II (cartilage)
§ Type III (fibrillar, blood vessels, reticulin)
§ Type IV (basement membrane)
o MULTI-ADHESIVE GLYCOPROTEINS
§ Fibronectin
§ Fibrinogen
§ Laminins (basement membrane)
o PROTEOGLYCANS
§ Aggrecan
§ Versican
§ Decorin
§ Perlecan (basement membrane
Connective tissues in ECM
Connective tissue is rich in ECM à all contain distinct spectrum of collagens, multi-adhesive glycoproteins and proteoglycans (ECM) together w/cellular component
· Each component is able to interact w/cellular components via specific cell surface receptors
· Many varieties of ECM component exist:
o COLLAGENS
§ Type I (bone, skin and tendon)
§ Type II (cartilage)
§ Type III (fibrillar, blood vessels, reticulin)
§ Type IV (basement membrane)
o MULTI-ADHESIVE GLYCOPROTEINS
§ Fibronectin
§ Fibrinogen
§ Laminins (basement membrane)
o PROTEOGLYCANS
§ Aggrecan
§ Versican
§ Decorin
§ Perlecan (basement membrane)
· Diff. types of collagen and diff. arrangements of oriented collagen coupled w/presence or absence of diff. ECM components generates wide variety of connective tissues
Collagen
COLLAGEN
o Family of fibrous proteins à found in all multicellular organisms
o Collagen biosynthesis – follows normal pathway for secreted protein
§ Collagen alpha-chains secreted as longer precursors, called pro-alpha-chains by ribosomes attached to rough ER
§ Pro-alpha-chains undergo series of covalent modifications + fold into triple-helical procollagen molecules, before release from cells
§ 3 pro-alpha chains collectively form procollagen chain
§ Subsequently undergoes cleavage, fibril formation and cross-linking
o Each collagen molecule made of 3 alpha-chains à can be homotrimer or heterotrimer
§ HOMOTRIMER à protein composed of 3 identical polypeptide units – TYPE II and III have only 1 chain type
§ HETEROTRIMER à composed of 3 subunits of which at least 1 differs from other 2 -TYPE I has chains from 2 genes so is heterotrimer w/composition [α1(I)]2 [α2(I)] i.e. 2 x alpha-1 and 1 x alpha-2 chains
o The alpha chains form a triple helix à primary sequence of collagen proteins has characteristic glycine-x-y repeat (x often=proline and y often=hydroxyproline)
o To form stiff helical structure every 3rd position must be occupied by glycine as it is the smallest amino acid
o Hydroxylation of proline is post-translational modification which contributes to formation of hydrogen bonds between chains
o Lysine and hydroxylysine are similarly modified in formation of covalent cross-linkages
o Cross-linking only occurs AFTER collagen has been secreted
§ Vitamin C deficiency à enzymes prolyl hydroxylase and lysyl hydroxylase need vit C co factor to function à underhydroxylated collagens à greatly affects tissue stability à scurvy
o Some collagens are fibril-associated à regulate organisation of collagen fibrils in tissues
o Staggered arrays of tropocollagen molecules form fibrils è ultimately arrange to form collagen fibres
Basement Membrane
o A.k.a basal laminae
o Flexible thin mats of ECM underlying epithelial sheets and tubes
o Highly specialised ECMs containing distinct collagens, glycoproteins and proteoglycans
o Collagen type IV molecules can associate laterally between triple helical segments as well as head to head and tail to tail between globular domains to give dimers, tetramers and higher order complexes à specifically in basement membrane
o BM surrounds muscle, peripheral nerve and fat cells and underlie most epithelia
o In the kidney, BM forms a key part of filtration unit as glomerular basement membrane
o In diabetic nephropathy à accumulation of ECM leading to highly thickened BM
Alport Syndrome
o Alport syndrome — mutations in collagen IV result in abnormally split and laminate glomerular BM, which is associated w/progressive loss of kidney function and hearing loss
EHLERS-DANLOS SYNDROME
o EHLERS-DANLOS SYNDROME — group of inherited connective tissue disorders – symptoms = stretchy skin and loose joints
Elastic fibres
o Often collagen and elastic fibres are interwoven to limit extent of stretching
o Elastic fibres à important for elasticity of tissues e.g. skin, blood vessels and lungs
o Core made of protein elastin and outer layer of microfibrils
o 2 types of segments that alternate along polypeptide chain à hydrophobic regions and alpha-helical regions rich in alanine and lysine
o Many lysine side chains are covalently cross-linked
Fibrillin
The integrity of elastic fibres depends upon microfibrils, containing the protein fibrillin.
Elastin
Elastin is an unusual protein consisting of two types of segments that alternate along the polypeptide chain: hydrophobic regions, and alpha-helical regions rich in alanine and lysine.
Many lysine side chains are covalently cross-linked.
Marfan’s syndrome
Mutations in the protein fibrillin-1 are associated with Marfan’s syndrome which has some diverse manifestations, involving primarily the skeletal, ocular, and cardiovascular systems.
Individuals can be predisposed to aortic ruptures.
Manifestations of Marfan’s syndrom include arachnodactyly (spider-like fingers).
Glycoproteins
GLYCOPROTEINS
o Mainly laminins (associated with BMs) and fibronectins
o Modular architecture à most ECM proteins are very large, makes them multifunctional
o Many large modular proteins ate multi-adhesive, binding various matrix components and cell surface receptors
Laminins
§ Heterotrimeric proteins made of alpha, beta and gamma chains which form cross-shaped molecules, very large proteins
§ Multi-adhesive à can interact w/a variety of cell surface receptors including integrins and dystroglycan
§ Can self-associate as part of basement membrane matrix, but can also interact w/other matrix components like type IV collagen, nidogen and proteoglycans
§ Mutations in specific chains associated w/inherited diseases such as muscular dystrophy and epidermolysis bullosa
§ Congenital muscular dystrophy à can arise from absence of alpha-2 chain in laminin 2, symptoms include hypotonia (decreased muscle tension – abnormal), generalised weakness and deformities of joints
Muscular Dystrophy // Epidermolysis bullosa
Pathology related to mutations in laminis
Mutations in specific chains are associated with inherited diseases such as muscular dystrophy and epidermolysis bullosa.
Congenital muscular dystrophy can arise from an absence of the α2 chain in laminin 2. Symptoms include hypotonia (abnormally decreased muscle tension), a generalised weakness and deformities of the joints.
Fibronectins
§ Family of closely related glycoproteins of ECM which are also found in body fluids
§ Derived from single gene w/alternate splicing of mRNAs giving rise to diff. types
§ Can exist either as insoluble fibrillar matrix or as soluble plasma protein
§ Also help to promote blood clotting
§ Multi-adhesive à made up of large multidomain molecules linked together by disulphide bonds
§ Able to interact w/cell surface receptors and other matrix molecules
§ Plays important roles in regulating cell adhesion and migration in no. of processes à notably embryogenesis and tissue repair
§ NOTE: fibronectins bind multiple ligands and cell receptors
Proteoglycans
o PROTEOGLYCANS = core proteins which are attached to 1 or more glycosaminoglycan (GAG) chains
o Proteoglycan families grouped by structural and functional characteristics
§ Small leucine-rich proteoglycans à decorin
§ Cell surface proteoglycans à syndecans 1-4
§ Aggregating proteoglycans (interact w/hyaluronan) à aggrecan
§ BM proteoglycans à Perlecan
Aggrecan
AGGRECAN:
§ Major constituent of cartilage ECM
§ Highly sulfated + carboxylated à increasing -ve charge
§ Attract cations like Na+ that are osmotically active
§ Leads to large quantities of water being retained
§ Under compressive load, water is given up
§ Regained once load is reduced à suited to resist compressive forces
GAG chains
o GAG CHAINS = made up of repeating disaccharide units w/1 or 2 sugars being an amino sugar (-OH
replaced by -NH3)
o Cartilage has a matrix rich in collagen w/large quantities of GAGs trapped within meshwork à balance of swelling pressure is negated by tension in collagen fibres, generating tensile strength
o Many GAGs are sulfated or carboxylated + so carry high negative charge à attracts clouds of cations including Na+ so lots of water sucked into ECM
o GAG chains grouped into 4 main groups according to repeat disaccharide units
§ Hyaluronan à spun out directly from enzyme embedded in plasma membrane
§ Heparan sulfate
§ Keratan sulfate
§ Chondroiton sulfate and dermatan sulfate
Hyaluronan : hyaluronic acid
§ In ECM of soft connective tissues
§ Simple carbohydrate chain w/o core protein
§ Unsulfated and made of repeating disaccharides
§ High degrees of polymerization
§ Occupy relatively large volume
§ Typically, of high viscosity e.g. vitreous humour of eye, synovial fluid of joints
Hyaluronan (also called hyaluronic acid) is found in the extracellular matrix of soft connective tissues. It is distinct form the other GAGs as it is simply a carbohydrate chain without a core protein. It is unsulfated and made up of repeating disaccharides which can number up to 25,000 sugars and is spun out directly from an enzyme embedded in the plasma membrane.
All the other GAGs are synthesised and attached to their core proteins in the endoplasmic reticulum and Golgi apparatus inside the cells.
Osteoarthritis and Fibrotic disease
OSTEOARTHRITIS and FIBROTIC DISEASE
o Osteoarthritis à erosive disease resulting in excessive ECM degradation – with increasing age, aggrecan is cleaved by aggrecanases and metalloproteinase à results in loss of aggrecan fragments to synovial fluid
o Cushioning properties of cartilage over bone ends lost
o Fibrotic disease à result of an excessive production of fibrous connective tissue
Epithelial cells
o Epithelial cells form continuous, cohesive layers of cells
o Requires cells to be well organised + to make stable cell to cell junctions
o Stability and maintenance key to function e.g. separating tissue compartments or lining surface of tissue
Single layer : simple epithelium — Fn: diffusion eg. Lungs
Multi-layer : stratified epithelium — Fn: Resisting chemical or mechanical stress
Squamous — flattened, plate shapes
Columnar — Arranged in columns
Cuboidal — cube like
Epithelial cells functions
Epithelial cell functions
o Membrane organised into discrete domains by formation of junctions
o At lumen (opening surface) à apical domain
o Pointing away from lumen in contact w/basal lamina à basolateral domain
o Most epithelial functions are directional à secretion, fluid + solute transport + absorption processes are highly organised
o Epithelial polarity needed to give directionality for epithelial function
§ Polarity in epithelial cells seen as diff. regions of cell surface different from one another w/discretely organised cellular contents
§ In transporter epithelia à channels like Na+/K+ exchangers must be polarised so passive ion and fluid flow occurs on one direction only – otherwise they pump baso-laterally and apically
§ Most epithelia secrete to either basal or apical aspect
o Cell to cell junctions in epithelia
o Different functions of epithelial cells
· Many epithelia constantly turned over i.e. cells lost by cell death or by mechanical removal e.g. abrasion à replaced by proliferation of the cells within epithelium
o Cells in intestinal crypts replacing cells lost from tips of intestinal villi
o Cells of basal layer of stratified squamous epithelia dividing to replace cells lost from surface
Cell to cell junctions in epithelia
Tight junction — Form belt usually around apical lateral membrane, involved in sealing gaps between cells
Adherens junction — Usually just below tight junction, least conspicuous junction under the microscope, but is essentially the master junction that controls formation of all others
Desmosomes — scattered throughout lateral membrane, are spot junctions that form mechanically tough junctions between cells, important in tissues that require to resist mechanical stresses
The 3 above form the junctional complex
Gap junction — Channel forming junction, form pores between cells and allows cells to exchange and share materials, communicating junctions allow cells to form communities and synchronise number of activities
Inflammation
rapid, non-specific response to cellular injury, universal process
· 4 main signs of acute inflammation
o Swelling
o Pain
o Redness
o Heat
o May also be loss of function
Acute Inflammation
Step 1: Change in local blood flow
Step 2: Structural changes in microvasculature
Step 3: Recruitment of immune cells + proteins
Acute inflammation: Step 1 – Change in local blood flow
INFLAMMATORY SIGNALS à non-apoptotic cell death, detection of PAMPs and DAMPs recognised by PRRs
§ PAMPs = pathogen associated molecular patterns e.g. lipopolysaccharide (LPS), lipoteichoic acid (LTA), peptidoglycan
§ DAMPs = damage associated molecule patterns (released when plasma membrane injured, or cell dies)
§ PRRs = pattern recognition receptors – activate cell, spark inflammatory response
o VASODILATORS RELEASED à histamine, nitric oxide
§ Histamine – from mast cells, basophils and platelets – cause vasodilation, increased vascular permeability, endothelial activation
Acute inflammation: Step 2 – Structural changes in microvasculature
o VASCULAR CHANGES à increased permeability, dilation, reduced flow, plasma leakage
Mediator release at injury
Histamines - From mast cells, basophils, platelets -> Vasodilation, increased vascular permeability, endothelial activation
Prostaglandins - From mast cells and leukocytes -> Vasodilation, pain, fever
Cytokines (TNF, IL-1) - From macrophages, endothelial cells, mast cells -> Endothelial activation (adhesion molecules), fever, malaise, pain, anorexia, shock
Chemokines - From leukocytes, activated macrophages -> Chemotaxis and activation
Complement (C5a, C3a, C4a) - From plasma (produced in the liver) -> Leukocyte chemotaxis and activation, vasodilation (mast cell stimulation), opsonisation
Acute inflammation: Step 3 – Recruitment of immune cells + proteins
o IMMUNE CELL RECRUITMENT à chemokines, produced at damaged site, diffuse to form gradient, WBCs (neutrophils + macrophages) w/complementary receptors migrate towards source
§ Chemokines – from activated macrophages – involved in chemotaxis, leukocyte activation
· Neutrophils are often the first cell type recruited to site of inflammation
· Other soluble mediators released at injury include:
o Histamine
o Prostaglandins
§ Principle sources à mast cells, leukocytes
§ Actions à vasodilation, pain, fever
o Cytokines
§ Principle sources à macrophages, endothelial cells, mast cells
§ Actions à endothelial activation (adhesion molecules), fever, malaise, pain, anorexia, shock
o Chemokines (CXCL8/IL8 -> Receptors: CXCR1 and CXCR2, g-coupled 7-transmembrane proteins)
o Complement proteins
§ Principle sources à plasma (produced in liver)
§ Actions à leukocyte chemotaxis and activation, vasodilation (mast cell stimulation), opsonisation
