cell adhesion 2

how is there cell adhesion to the ECM?

• fibronectin and integrals help attach cells to the ECM

• function as heterodimers

• transmit tension to across the plasma membrane

• anchored to the cytoskeleton

what is the role of fibronectin in the ECM?

• serves as a molecular bridge between integrins and ECM

• has ECM binding site (e.g. via collagen)

• has cell attachment site (e.g. via intern)

how does integrin regulation occur?

• regulated by signals from inside and outside the cell
• changes integrin conformation
• on/off integrin connections with the ECM enable cells to move through tissue
• made from alpha and beta subunits

how do integrins coordinate cell movement?

• new attachment points are established at the front of a moving cell
• old adhesions are released at the back
• enable the cell to 'crawl' forward

how do cells resist compression?

• collagen provides tensile strength to resist stretching
• Glycosaminoglycans (GAGs) resist compression
• chains of GAGs are linked to a core protein to form proteoglycans

what are the advantages of GAGs being negatively charged?

• keeps high (cation) in ECM
• draws in water
• creates swelling pressure

what do proteoglycans and GAGs form?

• can form very large aggregates
• tension in collagen fibres balanced by GAG swelling pressure
• matrix is tough

how do GAGs act as space fillers in connective tissues?

they are hydrophilic and adopt extended conformations relative to their mass

what is the ECM composition of tissue?

• dense connective tissue has less GAG and more collagen
• vitreous humour is almost entirely GAG and little collagen

what are some proteoglycan functions?

• binding growth factors
• controlling migration of cells through the ECM

what is epithelium?

• sheets of cells joined together side by side
• cover external surfaces and line all internal cavities

what is the role of epithelia?

• creates barriers
• controls movement of molecules in and out
• has receptors for external signals
• protects against invading microbes and fluid loss

what are the 4 types of epithelial cells?

• columnar
• cuboidal
• squamos
• stratified

what is the role of columnar epithelial cells?

secretion and absorption

what is the role of cuboidal epithelial cells?

secretion and absorption

what is the role of squamous epithelial cells?

filtration

what is the role of stratified epithelial cells?

protection

what is the basal lamina?

• a thin tough sheet of ECM
• separates the epithelial cells from the network of collagen fibres in the underlying connective tissue
• ECM composed mostly of type 4 collagen and laminin

where is the collagen and laminin in basal lamina from?

• collagen from underlying stromal cells
• laminin by overlying epithelial cells

what is the role of laminin?

• interacts with many proteins including integrins
• provides adhesive sites for integrins located in the basal membrane of epithelial cells
• similar role to fibronectin

what are the 2 types of epithelial polarity?

• apical
• basal

what is apical polarity?

when the surface is free and exposed to air or bodily fluids

what is basal polarity?

when the surface is attached to a sheet of connective tissue / basal lamina

what is the role of epithelial polarity in its function?

• gut is lined by absorptive epithelial cells
• contains secretory goblet (mucus) epithelial cells
• polarity is critical for function

what is the role of tight junctions as barriers?

• bind epithelial cells tightly to prevent leakage
• extracellular tracers can be stopped
• occluding and claudin seal interacting cells

what is the role of tight junctions in segregating membrane proteins?

• they block diffusion to keep apical and basal domains of the cell separate
• enables glucose transport against concentration gradient in from gut lumen and down its concentration gradient our into bloodstream