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72 Cards in this Set
- Front
- Back
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Four basic tissues in body
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epithelium, connective, muscle, and nerve
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2 functions of epithelia
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1. Form barrier
2. Conduct unidirectional transport |
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What are the embryonic sources of epithelia?
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All 3 germ layers
ectoderm- skin endoderm- GI, resp tracts mesoderm- endothelium, mesothelium, UG tract |
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classification of epi based on?
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Cell shape (of outer layer), number of cell layers, and types of surface specializations present
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Common Features of epithelia
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High cellularity vascularity (little EC material)
Avascular (except stria vascularis of ear) Innervated, often sensory High mitotic index (GI tract overturns 3-5 days; glandular epi is an exception) Most lie on a basement membrane, partly made by epi itself Attached by jxnal structures Polarized for fxn and unidirectional transport (eg, cilia on surface, organelles in the right sequence) |
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Basement membrane components
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Basal lamina (secreted by epi cells)
Reticular lamina (bed of fibers, usu collagen, secreted by underlying CT cells) |
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What type of epi lines body cavity and blood vessels
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Mesothelium (body cavity)
Endothelium (vessels) |
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Epi of skin?
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Stratified squamous, keratinized
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Inside of mouth?
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SS, parakeratinized (or no keratin)
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Vagina, esophagus?
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unkeratinized SS
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Where are cuboidal cells often found?
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Ducts of body, bronchioles of lung
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Simple columnar locations
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Digestive tract- stomach, sm. intestine, large intestine
Uterus |
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Stratified columnar
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In parts of anus, eye, male urethra
NOT ciliated |
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Pseudostratified columnar
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ciliated- trachea and upper respiratory tract
Nonciliated- membranous male urethra & vas def With stereocilia- ONLY in epididymis |
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Transitional Epithelium
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Bladder and part of urinary tract
Dome cells allow expansion |
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Alveoli type of epi?
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simple squamous b/c thin barrier
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Components of Basal lamina
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Type IV Collagen
Heparan Sulfate Laminin Entactin |
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Is Type IV collagen more or less stiff than other types? Why?
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Less, because heavily glycosylated. Has many flexible sequences and bends.
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Type IV Collagen composed of what?
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Small fibrils w/telopeptides attached that do not polymerize. Unique to basal lamina.
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Interaction of C-terminal and N-terminal ends?
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C heads interact to yield dimers
N tails interact to form network structure |
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What is Heparan sulfate?
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A sulfated glucosaminoglycan (N-acetyl glucosamine-SO4-iduronic acid)
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What does heparan sulfate do for basal lamina?
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Adds lots of negative charges
Plays a part in the selective filtration |
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What is laminin?
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Big glycoprotein shaped like a cross
1 alpha peptide 2 beta peptides (arms of cross) |
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What does laminin do?
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Binds components of basal lamina together & links them to the basal part of the epithelial cell
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Where do the different elements bind to laminin?
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Cell binds to top of cross (via integrin)
Collagen binds to arms of cross Heparan sulf. binds to bottom |
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What is entactin?
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sulfated glycoprotein- rod-shaped
Links laminin and collagen IV networks |
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Functions of basal lamina?
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Supports epithelium/separates from CT cells
Induces differentiation, influences metabolism of epi cells Acts as selective filtration barrier (esp in kidney) Permits cell migration (but blocks fibrocyte penetration) Provides scaffold for repair during wound healing |
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What happens when there's damage to basal lamina in the kidney glomerulus?
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Proteinuria occurs, since the BL acts as a filtration barrier.
Heparan sulfate helps with this function |
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Classes of junctional complexes
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1. Tight junctions (zonula occludens)
2. Anchoring junctions (adhering, desmosome, hemidesmosome) 3. Communicating (gap junctions) |
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Function of tight junctions?
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1. Form seal between lumenal and intercellular spaces
2. Maintains lumenal and basolateral membrane domains (so important for polarization of cell) aka zonula occludens |
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How is seal of tight junction formed?
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Integral membrane proteins in one cell fuse w/identical ones in adjacent cell
Contact is between proteins, not lipids |
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What two proteins make up tight junctions
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occludins and claudins
These are quadruple pass integral membrane proteins |
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what else do claudins do?
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Form tiny aqueous pores in the tight seal.
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Tightness of seal indicated by what?
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# of rows of proteins joined, % of claudins in the rows
More claudins=less tight Bladder- few claudins kidney- more claudins |
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Where is zonula occludens located on cell?
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In a belt around the apex
Also connected loosely to actin fibrils of cytoskeleton |
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What might cause an increase in number of strands in a tight junction?
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the presence of toxic agents
may work as a protective mechanism |
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Adhering junction
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belt-like structure circumscribing apical region of cell
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How do adhering junctions work?
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cadherin (transmembrane protein) of one cell binds to cadherin of adjacent cell
cytoplasmic ends of the cadherins bind to terminal web of cytoskeleton in apical regions of cells |
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Cadherin to cadherin binding is ___ dependent
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Ca+2
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What is the terminal web?
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a meshwork of actin filaments
it's held together by other binding proteins (eg alpha actinin, vinculin, talin) provides structure to apical reigon and an achoring site for actin core of microvilli contraction of web can alter cell shape |
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Binding of cadherin to actin filaments of terminal web is mediated by _____
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catenin
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Desmosome
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Ca-dependent rivet binding adjacent cells together
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How does a desmosome work?
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Cadherin proteins in adjacent cells bind to one another
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Where does cytoplasmic end of cadherin bind in a desmosome?
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To intermediate filaments (usu keratin) of cytoskeleton via a dense plaque
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Where does cytoplasmic end of cadherin bind in a desmosome?
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To intermediate filaments (usu keratin) of cytoskeleton via a dense plaque
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Electron microscope image of desmosome shows darkly stained, e- dense bands representing what?
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Ca+2 binding ends of cadherins
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Where are desmosomes common?
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In SS epithelum of epidermis, between muscle cells of the uterus, & cardiac muscle
These are places where stress exists between cells Desmosomes provide a very strong intercellular bond |
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Hemidesmosome
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Binds cells to ECM via integrins to laminins
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Structure of Communicating/Gap junctions
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connexons (hexameric transmembrane proteins) form tubes that line up with tubes in adjacent cells, forming patent cytoplasmic channels
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Purpose of patent cytoplasmic channel?
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permit free intercellular exchange of substances of 1000 daltons or smaller (Na, ATP, cAMP)
also permit intercellular electrical coupling and signalling promote metabolic synchrony of cells |
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What affects patency of connexons?
What's their turnover rate? |
ph and Ca affect patency (acidity and high Ca cause closure-- safety mechanism for adjacent cells)
High turnover rate- 19 hours |
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Cadherins: ___ dependent
associated with ____ and ____ Connect to ____ or _____ of cytoskeleton |
Ca+2
Adhering junctions & desmosomes actin or keratin components of cytoskeleton |
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Ig super family contain?
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repeating units similar to IgG
sialic acid resides |
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Ig involved in?
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Cell to cell binding (more IgG content = stronger binding, more sialic acid = weaker)
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Integrins
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Ca or Mg dependent, single pass, heterodimeric
Bind cell to matrix by connecting cytoskeletal elements to collagen, fibronectin, or laminin of ECM in hemidesmosomes |
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Selectins
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Single pass membrane proteins that contain lectin components (carb-binding regions)
Bind cell-cell via carbs |
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Asymmetry of epithelial cells
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They're polarized to allow them to perform specific functions
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Apex of epi cells
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Cilia, microvilli, stereocilia,
the glycocalyx |
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Laterally on epi cells
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Plasma membrane interdigitations
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Basal side of epi cells
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Basal infoldings
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Apical plasma membrane domain characteristics
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Na+ permeable, Na-glucose co-port
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Basolateral plasma membrane domain characteristics
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Na,K ATPase, glucose carrier transport
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Polarization of organelles for protein synthesis
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RER--> Golgi --> Secretory vesicles --> Plasma membrane release
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Specialized cells w/in epithelium
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goblet cells, endocrine cells, lymphocytes, sensory cells
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Microvilli structure
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supported internally by actin core
anchored to cytoplasmic actin (maybe the terminal web) covered by plasma membrane |
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Location of microvilli
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As brush border (intestine) or striated border (proximal tubule of kidney) on cell apices involved in absorption
or single and vary in size & regularity on many epi cell apices |
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Location of microvilli
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As brush border (intestine) or striated border (proximal tubule of kidney) on cell apices involved in absorption
or single and vary in size & regularity on many epi cell apices |
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Glycocalyx
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composed of membrane glycoproteins
provides protection for cell surface may provide recognition sites may adsorb digestive enzymes (intestinal tract) |
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Cilia/flagella structure
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axoneme core of microtubules in 9+2 pattern
covered by plasma membrane supported by basal body (in cytoplasm) consisting of 9 triple microtubules |
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Motility of cilia/flagella
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Usually motile
Dynein arms crawl down each other and allow beating action Single, nonmotile cilia found in various locations and may serve sensory functions (kidney, testis, gland ducts) |
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Stereocilia structure
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Actin core covered by plasma membrane
Long, immotile May connect to each other by cytoplasmic bridges, may be branched |
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Stereocilia location
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Rare-- limited to epithelium lining tubules of male reproductive tract
Hair cells in ear may also contain stereocilia specialized for sensation |
