Objectives 1) Microscopically identify the diff. types of epithelia tissue 2) Relate the structure of epithelia to its role in protection, surface transport, absorption, secretion, and forming selective permeability barriers. Define cell polarity and how it relates to epithelial absorption and transport. 3) Describe the structures and function of epithelial specializations, including microvilli, cilia, junctional complexes, and basal membrane enfoldings. Relate these to the functions of the organs where they're found. 4) Describe the structures of cell junctions and how each type of junction relates to epithelial functions. Recog. relationship between cytoskeleton and cell juctions. Appreciate the relationship between junctional proteins and skin disease. 5) Define 'basement membrane' and how it relates to 'basal lamina.' Understand the relationship between epithelial cells and the basal lamina. Appreciate how defects in basal lamina proteins relate to diseases of the skin. 6) Define terminal web, terminal bar, and junctional complex and appreciate how they are related structurally and functionally. - There are 4 main tissues: epithelia, connective tissue, muscle, and nervous tissue - Epithelia arise from all 3 embryonic germ layers: !- ectoderm (oral and nasal mucose)!- mesoderm (lining of GI and resp.)!- endoderm (Mesothelium covers mesentary and some organs and endothelium lining circulatory system)!Functions of epithelia:!- barrier, transport and secretion, sensory reception, regeneration and reproduction!Common Properties of Epithelial Cells - the cells are attached to each other by adherens junctions-->ensure wall maintenance!- occluding junctions seal the intercellular spaces!- polarized transport systems in the membrane for unidirectional transport - sep. from underlying tissues by a basement membrane!- there is a little interstitial fluid in the epithelium!- there are no vessels= it is avascular, but there are nerve endings Classification of Epithelia - the top most layer of the cells gives us the classification!Simple Squamous Epithelium - 1 layer, exposed to outside, large flat nuclei bulging out!- Involved in exchange of fluid, gas and metabolites!- found in lung, kidney, endothelium, and mesothelium !!!Simple Cupoidal Epithelium - Forms a covering for absorption and secretion!- Found in the ducts and ovary!!Simple Columnar Epithelium - Involved in protection, secretion, absorption, surface !transport!- Found mostly in GI, ovidcut, ducts!- May have cilia, microvilli, and goblet cells!!- Goblet cells: unicellular glands in epithelium!-they have mucus inside them in secretory granules that can be used as a lubricant, protection, and water retainer. Can also capture pollutant particles in lung.!- there is regulated secretion of mucus by goblet cells! !!!!!Stratified Squamous Epithelium - Involved in protection!- May found w/okeratin (moist envi= mouth, vagina) or w/keratin (dry envi= skin) !!Pseudostratified Columnar Epithelium - Involved in protection, secretion, and surface transport!- WITH cilia and goblet cells!- Respiratory tract!- Nuclei look at diff. levels, but still all in cells that rest upon the basal lamina. It's not multilayer.!!Transitional Epithelium - Involved in protection and distensibility!- Found in urinary tract!- Can tell apart from stratified squamous !epith. which has many more layers!- Also has gaps/spaces between cells when relaxed!!!!!!!!!!!!Model of Simple Epithelial Cells !!!!!!!!!Epithelial Cells Domains !!!!!!!!!!!!!!Structure and Function of Basal Lamina - Support for epithel. cells because specialized cells receptors can bind to it!- Involved in differentiation by signaling thru integrins!- Cell migration, filter for large particles, wound response, role in cancer mestasis (cross BL)!- Basal lamina: lamina rara + lamina densa, EM term!- Basement membrane: basal lamina (lr+ ld) + reticular lamina, LM term!- invaginations in bl (basal infoldings) greatly increases SA of om!!Junctional Complexes of Epithelial Cells ! Unidirectional transport in polarized epithelial cellHemidesmosomes= provide integrity for the tissue-->interact with the basal lamina-->solid cell/bl relationship!- have integrins= a tm receptors, tm signaling. Adhesion protein.!- made up of integrins, adaptor proteins (ex. Plectin--links bl to intermediate filaments)!!Tight junctions= zonuula occludens= occluding junctions!- cytoskel= actin!- form barriers between the apical and basolateral domains!- control paracellular transport !- leaky TJ's (ex. in intestine) have a shunt thru it to the intracellular spaces!- defect in claudin 16-->no paracell flow of Mg!- reg. by Rho proteins!!Adherens Junctions - kind of organized like a belt around the cells!!Desmosomes= Macula adherens - specialized adhesive protein complexes that localize to intracellular junctions, resp. for maintaining mechanical integrity of the tissues!- in freeze fracture= circle with proteins of irregular sizes!!!!!!!!!!Gap Junctions - allow communication between cells: metabolic and electrical coupling of adjacent cells!- in FF: highly packed proteins!- made of connexin protein, takes 6 on each cell side to make a channel!- only lets molecules of certain sizes pass thru (up to 1000 MW), 2nm diameter channel!- permeability can be reg by Ca, pH, and phosphory of connexins !!Glycocalyx - carbohydrate coat that's present on the apical cell surface!- protects the cell surface and mediates cell to cell interactions!- found on intestinal epithelia, it's rich in digestie enzymes!!Cilia and Microvilli (apical domain)!- If nucleus diameter is sim to top projection= cilia!- if surface projections are much much smaller than nuclei= microvilli!!Microvilli and the Terminal Web - primarily actin filaments Other Terms - Terminal bar= a LM term, dark lines on edge of cells, made up of all the junctional complexes on the lateral side of the cell (but for test: just adherens and occluding junctions)!- Junctional complex= an EM term, you can actually differentiate between the junctions!- Stereocilia (modified microvilli)!- find it as hair cell= sensory cell of the ear and in epididymis!- can tell it apart from microvilli because it doesn't have the classic terminal web and it
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