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| Question | Answer |
| Extracellular matrix | - ECMs are excreted by, and surround cells. - In the human body there are 2 types of ECMs: 1. Epithelium: in which cells are tightly packed 2. Mesenchyme: within which cells are sparse |
| Basal lamina AKA basement membrane | - Barrier between ECMs- 2D sheet on which epithelial cells reside. - Found in all body tissues, wraps many organs - Filters urine in the kidneys - Made of proteins and sugars, with big proteins such as collagen |
| Fibrillar matrix | - Exists in the mesenchyme, cells are buried in here - In the 'deeper part' of the skin - made up of many cells, making it 3D, which remodel it - Degregation of the fibrillar matrix is the reason for wrinkles as we age |
| Cell junctions | - Junctional complexes are the structures of the cells that enable cell division - Observed using electron microscopy - ^different types: 1. Demisomes 2. Hemidemosomes 3. Tight junctiobs 4. Gap junctions 5. Adherens junctions 6. Focal adhesion |
| Cell Junctions 1 & 2- Demosomes and hemidemosomes- Connect intermediate filaments in one cell to those in the next/extracellular matrix | - Pairs of dark, disk-like structures at cell-cell contacts - Seems to join cells together - hemidesosomes- half desosomes; bond cells to ECMs - Size: Desosomes about 500mn tall Hemidesosomes about 100nm wide - Anchor intermediate filaments inside cells - Intermediate filaments protect the cell against mechanical stress, are anchored together by desosomes and to the basal lamina (basement membrane) by hemidesosomes - Therefore hemi/desosomes help strengthen cells - They have similar function/appearance, but different components - If defective, causes fragility of skin/other epithelia |
| Cell junctions 3: Tight junctions- seals gap between epithelial cells | - Tight junctions are where 2 cells have membranes tightly attached to one another - Form net-like membranes, sealing together strands of tight junction proteins - Act like a headband, sealing the apical circumference of the cell - Function: 1. 'Fence'- ensuring cells are localised so they can properly carry out their function 2. 'Barrier'- keeps useful molecules inside the body, blocks harmful ones from invading the tissue - If tight junctions become defective: skin permeaility is abrogated EG of water diffusing out of mouse pup with defective tight junction proteins |
| Cell junction 4: Gap junctions- allows passage of small water soluble molecules from cell-cell. | - Located in the side of cells, underneath tight junctions - 'channels' between cells - Ions and small molecules can diffuse through |
| Cell junction 5: Adherens junctions- involve cadherin in connecting actin filament bundle in one cell to that in the next | - main component is cadheren; a transmembrane protein that mediates calcium movement between cells - In epithelial cells, e-cadherin is the main component, underneath which is a bundle of actin and myosin. - This bundle of actomyosin 'squeezes' the cell at he adherens junction, providing the motile force for epithelial folding - Cadherins cause cell sorting |
| Cell junction 6: focal adhesion- involve integrin in their roles in cell movement, anchoring actin filaments in the cell to the extracellular matrix. | - Large multi-molecular assemblies that include integrins, which bind to the ECM outside the cell - Inside the plasma membrane of the cell, integrins are connected to actin filaments by linker proteins - Used by cells to walk on/deform ECMs; facilitate contraction of actin in cell movement |
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