Lecture 5 Flashcards
(13 cards)
Lateral membrane specialisation
Close apposition with adjacent cells. Adhesive and communicative. Junction complex is located on top part of epithelial cells and they are like the 6 rings round a pack o beer in terms of structure. They are tight and adhesive and they assist with communication between the inside and external environment as well as between cells. There are other localised junctions located below the junctional complex and they have desmosomes and gap junctions. Aim is to separate the apical membrane and baso lateral membrane.
Tight Junctions
AKA zonula Occludens, occluding junctions. Most apical. Controls paracellular movement and separates internal and internal environments. Interconnecting strands of proteins (occludin) and junctional strands (clauding) that regulate permeability as theres lots of isoforms of claudins that allow different ions to travel through. Different junction depthh and claudin molecule types allow them to be either leaky (allow lots of ions and water through) or tight (dont let anything through)
Adherens junctions
Intermediate junction. Adhesive belt around apical region of cell. Anchors terminal web (actin) connecting the apical cytoskeleton of adjacent epithelium. Lateral adhesion of cells. Cadherins link together intercellularly and allows cells to maintain shape and flexibility.
Desmosomes
Macula adherins meaning spot welds. Discrete spots of cellular attachments. Very strong mechanical adhesion. Dense plaque on cytoplasmic side of lateral pm. Filaments in extracellular space. Plaques anchor intermediate filaments.
Gap junctions
communicating junction. Discrete spot on lateral pm. Usually located well below other junctions. transport of ions between cells, metabolites and other molecules. Only junctions that allow a direct passage of signalling molecule from one cell to the next. Connexin proteins form connexin channels. Look like honeycomb.
lateral interdigitations
infolding of lateral membrane. Fit together like jigsaw puzzle. Increase SA good for pumps and channels.
simple squamous
exchange. Often permeable, allowing passage of material via diffusion/filtration e.g lung alveoli. endothelium and mesothelium.
stratified squamous
wear and tear epithelium. Lots of desmosomes and hemidesmosomes to hold cell in place. Found in areas containing fluid/moist surfaces and those exposed to air/abrasion. Rapid turnover. Non-keratinised in oral cavity, oesophagus and vag. keratinised layer on skin to resist abrasion, water soluble protein. lots of desmosomes.
simple cuboidal
absorption and secretion. Have more space for organelles than squamous. often microvilli on apical surface. Duct, kidney, thyroid follicles
simple columnar
most strikingly polarised. Secretion and/or absorption. Gut, respiratory, female reproductive system. Lots of microvilli
stratified cuboidal and columnar
barrier, conduit, protection, secretion, rare. 2-3 cells thick. some ducts of glands. Stratified columnar
pseudostratified epithelium
protection, secretion. often have cilia. Large airways, male reproductive system
transitional epithelium
protection, osmotic barrier. Bladder, urinary system. Transitory thickness (empty bladder-several layers thick, full bladder 2 cell layers seen). Apical cells dome shaped, binucleated. Refractile boarder.
