MBC - Epithelial Cells and Tissues Flashcards
Tissues
Group/groups of cells whose type + organisation + architecture are integral to function, made up of cells + ECM + fluid
Extracellular matrix
Material deposited by cells that forms insoluble part of extracellular environment, fibrillar (reticular) proteins (ie collagens, elastin) embedded in hydrated gel (proteoglycans), poorly organized (loose connective tissue)/highly organized (tendon, bone, basal lamina)
Cell types
Connective tissue cells (fibroblasts (many tissues), chondrocytes (cartilage), osteocytes (bone)), contractile tissues (skeletal, cardiac, smooth muscle), hematopoietic cells (blood, tissue-resident immune and bone marrow cells), neural cells (nervous system, neurones carry electrical signals and glial cells support cells), epithelial cells (form continuous layers that among other functions line surfaces and separate tissue compartments)
Tumours
Retain characteristics of cell type from which they originate, epithelial = carcinomas, mesenchymal (connective tissue/ muscle) = sarcomas, hematopoietic = leukaemias (bone marrow)/lymphomas (lymphocytes), neural cell = neuroblastoma (neurones)/gliomas (glial cells)
Epithelial cell classification
Single squamous = alveolar epithelium, mesothelium (lining major body cavities), endothelium (lines blood vessels and other blood spaces), form thin epithelium to allow gas exchange
Simple cuboidal = duct lining (ie kidney collecting ducts)
Simple columnar = surfaces for absorption and secretion (ie enterocytes)
Stratified squamous = keratinising (produces keratin and in doing so dies (becoming thicker and stronger protective structure ie epidermis), lose cellular organelles and nuclei, physical and chemical insults (ie heat, cold, solvents, abrasion), non-keratinising (mouth, esophagus, anus, cervix, vagina), cell shapes vary in layers but surface cells = squamous
Pseudo-stratified = multi-layered, surface cells in contact with basal lamina, trachea and bronchi, ducts in urinary and reproductive tracts
Epithelial organization
Organized and stable cell-cell junctions to form continuous and cohesive layers that line internal and external body surfaces and have various functions (transport, absorption, secretion and protection)
Epithelial cell polarity
Membrane organized in domains by formation of junctions (membrane polarity) = distinct polarity (apical domain at lumenal (open) surface and basolateral domain), basal surface in contact with ECM, membrane between 2 surfaces = lateral, most epithelial functions = directional (secretion, fluid and solute transport + absorption) an highly organized, polarity (different regions) required for directionality (either to interstitial or basal space)
Cell-cell junctions
Tight = belt around apical lateral membrane, seal gaps between cells, adherents controls formation of all others, desmosomes = lateral membrane, spot junctions = mechanically tough, gap = pores between cells, communicating junctions exchange and share materials
Transporting epithelia
Plasma membranes contain high concentration of ion transporters, mitochondria closely associated with basal membrane in folding (energy for active transport, increase amount of basal membrane that can pump ions and H2O directionally
Absorptive epithelium
Carriers transporting nutrients, microvillous brush-border membranes (ie absorptive intestinal cells (enterocytes) and kidney proximal tubule cells, villi covered with intestinal epithelial cells, microvilli = plasma membrane villi projections, secretory cells (goblet cells secreting mucus) interspersed among absorptive cells of intestinal villi, intestinal cells have microvillus brush border (BB) with large amounts of active transporters and channels for nutrient uptake from gut lumen (as concentration of nutrients increases in cytoplasm of absorptive cells it diffuses down its concentration gradient into basal interstitial space to be collected by capillaries))
