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31 Cards in this Set
- Front
- Back
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Epithelium purpose
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Junctions between cells, cell surface specializations
- Tend to line cavities/surfaces or cover organs |
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Epithelium overview/characteristics
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- Generally very little space between cells
- Cells adhere to one another (have connections) - Cells involved in transport of materials b/w compartments - Often exhibit polarity |
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Terminal bar
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junction complex at apical end of cells, binds adjacent cell
- Composed of Zonula occludens (tight junctions) and Zonula adherens (belt desmosome) |
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Tight junction (zonula occludens)
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No cytoskeltal elements involved
- Protein/lipid fence - keeps basal, lateral proteins from diffusing to apical side, vice versa - Ion gate - very selectively permeable, keeps most things from diffusing (except some ions) - Proteins - claudin, occludin, ZO-1, ZO-2 |
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Belt Desmosome (zonula adherens)
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Lots of actin filaments inserted, involved here
- Also, many membrane proteins span the gap, connect the two cells - Anchors cell to neighboring cell - Terminal web - actin filaments connected at web on apical side of cell |
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Zonula occludens vs. zonula adherens
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Occludens is more for function - separating proteins/lipids/ions
- Adherens more for solid structural support |
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Spot desmosomes (macula adherens)
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Macula - spot (immaculate has no spots...)
- Very strong connection b/w neighboring cells - Supported by IF's from both cells |
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Hemidesmosome
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Connects cell to ECM, connective tissue
- Keratin - IF common to epithelium - important in desmosomes/hemidesmosomes |
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Carcinoma source ID
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Many times by keratin type
- Carcinoma means it came from epithelial tissue |
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Gap junctions
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For cell-cell communication
- Function via connexons (connexin subunits) - Not associated with any particular part of cell - Ions, small regulatory molecules (cAMP, etc.) can pass, but proteins can NOT - Regulated by intracellular Ca2+ - when cells dying, etc = Ca2+ release stimulates connexon close |
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Microvilli
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Appears to be "brush-like" border - can't see individually with light microscope
- Allow 30x more surface area than if flat - Actin microfilaments extend up microvilli - also plugged into the terminal web - Glycocalyx - fuzzy layer that extends off ends of microvilli - sugar residues from proteins, glycolipids |
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Microplicae
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Ridges at surface of some specific epithelial cell types
- Not visible with light microscope - Shaped by actin microfilaments |
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Stereocilia
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Immobile cilia
- Also shaped/supported by actin micro filaments - Much larger than microvilli, can be seen by light microscope under right conditions - Stereocilia in hair cells in cochlea |
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Basal foldings
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Foldings on basal side of cell
- Increase surface area of cell for transporting things in/out of cell |
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Cilia & Flagella
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MT structures Motile = 9+2, primary (non-motile) = 9+0
- Primary cilia involved in signalling - lack, defects = diseases - Flagella is longer, singular - Cilia are shorter, many together |
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Epithelial polarity
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Apical = luminal, mucosal side
- basolateral = serosal, abluminal - Polarity is key for transport! - Ex. - Na+/K+ ATPase on basolateral side puts in K+, out Na+ - This creates gradient for moving Na+ into cell - Na+ channels on apical side, etc. |
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Epithelial "secretion" ambiguity
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- Secretion can have a couple meanings
1) Tranport from basolateral -> apical = secretion (opposite = absorption) 2) Endocrine/other product made/stored in cell, released EITHER into lumen or blood (basolateral side) |
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Endocrine-style secretion methods
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Merocrine, apocrine, holocrine
- Merocrine - products in granules released via exocytosis - no part of cell is lost/damaged - Apocrine - like milk production - lipid bundle moved to surface via lipoproteins - membrane pinched off, part of cell goes with droplet - Holocrine - whole cell is part of secretion |
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Constituitive vs. regulated secretion
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Constituitve - by default cells are constantly producing, releasing these products (serum albumin in liver)
- Regulated - more common - cell makes/receives product, stores it until stimulated, then releases |
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Protein secretion cells
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1) Serous cells - produce protein, and watery material that looks like serum
- Histologically, serous cells produce proteins/enzymes = cytoplasm stains well 2) Neuroendocrine cells - usually from neural crest cells, migrate elsewhere - endocrine cells though, so secreting into the bloodstream - can see granules on basolateral side with scanning EM |
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Mucus secreting cells
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Mucus cells - produce mucins (hydrated glycoproteins), excrete @ lumenal side
- Most protein producers pack products into granules - mucus cells different - hydrated glycoproteins large and springy, don't stain well with eosin, hemotoxins - Mucins occupy large volume - nuclei of cells often pushed to basal side of cell |
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Serous vs. Mucus cells
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Serous smaller, cytoplasm stains well, nuclei in the middle-ish
- Mucus are larger, stain poorly (if at all), nuclei squished to bottom |
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Goblet cell
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Mucus cell that is surrounded by other non-mucus cells
- Glycoprotein granules push up to lumenal surface, displace other organelles - Produces goblet-like appearance |
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Review protein secretion...
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mRNA -> splicing -> translation -> packaging, use...
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Steroid secreting epithelial cells
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Steroids = fat soluble - diffuse through plasma membranes = vesicles won't hold them...
- Thus, products of these cells simply diffuse out of cells - different from other 3 secretion methods - Lots of smooth ER - Mitochondria with tubular cristae - Lots of fat droplets (raw materials) |
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Myoepithelial cells
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Epithelial cells at the base of epithelia involved in contraction
- Contract, help expel secretions from the lumen of secretory units - Have some smooth mm. actin - Sweat, mammary, tear, and salivary glands/ducts have these... |
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Basement membranes
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Older term = basal lamina, but they are the same thing
- Typically on basal side (blood side) of epitheial cell - Basement membranes also surround muscle and nerve cells - Lamina densa, lamina rara (one or more), lamina reticularis (not actually part of membrane) - Densa and rara = artifacts of dehydration... |
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Basement membrane components
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Type IV collagen - doesn't form fibrils - meshwork instead
- Laminin - Heparan sulfate proteoglycans |
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Basement membrane function
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- Anchoring substrate for cells
- Signal template for differentiation - signals regenerating cells to become certain type - Filter for molecules - renal glomerulus - Filter for cells - keep cells in certain parts of body |
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Metastasis mechanism
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Diapedesis - enzymatically degrade BM
- Rule of 3 BM's to cross - 1) escape from tumor 2) into blood 3) out of blood to other tissue |
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Epithelial naming
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Cells named by shape at lumenal surface
- Simple - means only one layer of epithelium - Stratified - more than one layer - Pseudostratified - looks stratified (jumbled nuclei) - but all cells reach BM (lungs) - Keratinized - whether lose nucleus, organelles or not - Squamous = very flat, almost looks like line... - Cuboidal = rougly same height, width - Columnar = much taller than width - Transitional epithelium - can stretch, unstretch - can look squamous or round & plump - urinary tract |
