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UKCD Histo Lec 2
Answers to Learning Obj questions
| Question | Answer |
|---|---|
| What are the two major categories of epithelium and how do they differ | Membranous and secretory (glandular). Membranous epithelium is found arranged in sheets. Glandular epithelium is generally in clumps and/or cords of cells that may or may not be connected to the epithelial surface from which it arose. |
| What are the two major categories of epithelium and how do they differ? | Membranous and secretory (glandular). Membranous epithelium is found arranged in sheets. Glandular epithelium is generally in clumps and/or cords of cells that may or may not be connected to the epithelial surface from which it arose. |
| What is meant when it is said that epithelial cells exhibit polarity? | They have defined surfaces (domains) based on their attachment to the basement membrane. |
| What are the 3 surfaces/domains each cell exhibits? | Apical, lateral, and basal (sometimes the latter two are collectively referred to as basolateral |
| What is the function of each cell surface and what are they specialized for? | Basal - attachment, transport; Apical - absorption/secretion; Lateral - attachment/ communication. |
| List three functional epithelial types | Transporting, absorptive, and secretory epithelia |
| List the three foremost characteristics of epithelial tissue. | Relative absence of intercellular substance, avascular, exhibit spolarity. |
| How are epithelial cells nourished? | By diffusion from blood vessels of the underlying connective tissue. |
| What are the two component parts of the basement membrane? | Basal lamina and reticular lamina |
| What are the two components of the basal lamina seen with TEM? | The lamina densa and lamina lucida |
| What is each component of the basement membrane composed of? | The basal lamina is composed of type IV collagen as well as enriched with laminin and fibronectin molecules; the reticular lamina is primarily type II colaagen (reticular fiber-like). |
| What forms/secretes each component of the basement meembrane? | The basal lamina (both components) is secreted by the overlying epithelial cells. The reticular lamina is secreted by fibroblasts of the underlying connective tissue layer. |
| What are the functions of the basement membrane? | Structural attachment, filtration and polarity induction are the main three |
| What happens if the basement membrane deteriorates? What are the implications of this component in wound healing? | Dettachment of the epithelial membrane lying above it. Can result in ulcer formation in the tubular gastrointestinal tract and delay wound healing. |
| What are the two basic types of epithelium? | Membranous (lining) and glandular (secretory). |
| What are the two main classes of membranous epithelium? | Simple and stratified |
| How is membranous epithelium classified? | By the number of layers of cells above the basement membrane and the cellular morphology of the uppermost layer. |
| List the 3 types of simple epithelium and give and example of each. | Simple squamous (endothelium/mesothelium); simple cuboidal (surface lining of ovary); simple columnar (lining gallbladder). |
| List two types of modified simple columnar epithelium and give and example of each. | Simple columnar secretory epithelium (lining of duodenum throuigh colon); simple columnar ciliated epithelium (lining of uterine tube). |
| List the 4 main types of stratified epithelia and state where each could be found. | Stratified squamous - skin; stratified cuboidal - ducts of sweat glands; stratified columnar - lining large ducts of major glands, transitional epithelium - lining of the urinary bladder/ureter. |
| How do the two types of stratified squamous epithelium differ? | Stratified squamous nonkeratinizing no keratin in the cells and nuclei persist Stratified squamous keratining soft keratin in the cells that kill the cell so the nuclei are absent and the dead cells are little more than squames (tiles) of keratin. |
| Where would you find an example of each type of stratified squamous? | Stratified squamous nonkeratinizing is found lining the vagina and esophagus; (areas of wear and tear), while stratified squamous keratining epithelium is found comprising the skin |
| How does transitional epithelium get its name? | The cells of the uppermost layer of this stratified form of epithelium “transform” between cuboidal in a relaxed state to squamous in the stretched state. |
| Where would you find transitional epithelium? | urinary bladder and ureters |
| What might transitional epithelium's "stretched" configuration be mistaken for? | Stratified squamous nonkeratinizing epithelium. |
| What does the term pseudostratified mean? | This membranous epithelium “appears” stratified but in actuality it is not . “Pseudo” means false. |
| What can be said about ALL cells in a pseudostratified epithelium? | Every cell in the pseudostratified columnar epithelial lining makes contact with the basement membrane but NOT every cell contacts the apical surface |
| What other types of cells, and/or surface specializations, are commonly found associated with pseudostratified columnar epithelium? | Goblet cells and cilia. |
| List the functions of the cytoskeleton | Cell movement, support, phagocytosis, cytokinesis, cell-cell and cell-extracellular matrix adherence, changes in cell shape. |
| List the 3 cytoskeletal components in order of increasing size (diameter) | Microfilaments, intermediate filaments, microtubules |
| What is the main structural component of microfilaments | Actin (G-actin specifically |
| Actin polymerization (growth) is dependent on what specific molecule? | Adenosine triphosphate (ATP). |
| What is treadmilling? | The orderly pathway of ATP-congugated G-actin monomers from the plus end of the F-actin chain during which they become depolymerized and dissociate from the minus end of the filament. |
| What causes depolymerization (dissociation) of the F-actin filament? | The hydrolysis of the ATP conjugated to the G-actin monomers to ADP (adenosine diphosphate). |
| Name three actin-binding proteins and state their general function | Thymosin, profilin and gelsolin. They participate in the assembly and disassembly of actin filaments |
| Where are microfilaments predominantly found in all cells? why? | Peripherally as they participate in actin-binding proteins associated with the plasma membrane and cell-cell/cell-extracellular matrix interactions. |
| What is the terminal web? Where is it located? What is its function? | A meshwork of intermediate filaments across the apical region of the cell. It links into the junctional complex of epithelial cells and allows cilia and microvilli of the apical surface to anchor into it’s mesh. |
| Why are intermediate filaments the most stable cytoskeletal structures? | They do not fluctuate between assembly and disassembly states. |
| What regulates the assembly and disassembly of intermediate filaments? | Phosphorylation. |
| With regard to intermediate filament construction, list the proper order of structural assembly. | Monomers form a parallel dimer; 2 dimers form a tetramer; tetramers align to form a protofilament; pairs of protofilaments associate laterally to form a protofibril; 4 protofibrils form a twisted intermediate filament. |
| Name some common intermediate filaments related to epithelial cells. | Keratins (acidic, neutral and basic) |
| Name some common intermediate filaments related to neurons. | Peripherin, glial fibrillary acidic protein (GFAP), and neurofilaments. |
| What are the structural units of a microtubule? | Tubulin dimers (alpha and beta) |
| What controls microtubule assembly? | Low calcium concentration and guanosine triphosphate (GTP) |
| How do microtubules differ morphologically from microfilaments and intermediate filaments? What does this difference contribute functionally? | Microtubules are hollow and this imparts a greater structural strength/rigidity. |
| What does dynamic instability means with reference to microtubules? | They undergo alternate phases of slow growth and rapid depolymerization resulting in a continued and rapid turnover. |
| Identify one type of highly unstable microtubule assembly within a cell. | The Microtubule Organizing Center (MTOC) that gives rise to the mitotic and meiotic spindles. |
| Identify one type of highly stable microtubule assembly within a cell. | Microtubule-Associated Protein (MAP) stabilized microtubules of neurons. |
| What is a microtubule protofilament? | A vertical column of alpha and beta tubulin monomers within the wall of a microtubule. |
| How many protofilaments form a microtubule? | Thirteen. |
| What is the microtubular configuration within a centriole and what is the function of this organelles? | Kenesin (anterograde) and dynein (retrograde). |
| Name two important MAPs associated with cellular transport within a neuron and the direction each one moves the vesicles along the microtubule. | Kenesin (anterograde) and dynein (retrograde). |
| State the configuration of microtubules with the basal body and axoneme of a cilium/ flagellum | In the basal body there are 9 peripheral MT triplets, in the axoneme there are 9 peripheral doublets (with a third incomplete MT) and two central singlet MTs. |
| What structures are responsible for creating movement of the cilium/flagellum? | The inner and outer dynein arms of the MT doublets. |
| State some clinical examples of cilium/flagellum dysfunction. | Sterility in males and females, stasis of mucus causing infections/congestion |
| What is the function of action microfilaments in the intestinal villi? | Structural support, limited contractility |
| List two actin-linking proteins, two actin-binding found in intestinal villi and the function of each | The actin linking protein are villin and fimbrin link actin filaments to one another; the actin- binding proteins are myosin-I and calmodulin that bind the filaments to the villus plasma membrane. |
| State the specific adhesion protein that functions primarily in holding epithelial cells together in a sheet. | Cadherins |
| What are catenins and what is their specific function? | They are linking protein that bind to each other and in turn link cadherin molecules to the actin filaments of the cell cytoskeleton. |
| How do desmosomes differ from zonula adherins with respect to the specific cytoskeletal unit associated with each. | Zonula adherens have actin microfilaments associated with their intracellular aspect where as desmosomes are associated with intermediate filaments (keratin tonofibrils). |
| What do these structures have in common? | Both share a cxommon function - attachment; both utilize caherins in their extracellular attachment component. |
| What are integrins. What is their general function? | A transmembrane protein family. They function in binding the cell surface to the extracellular matrix/basement membrane. |
| How are integrins structurally composed? | Integrins are composed of two different subunits (alpha and beta). |
| To what does the beta integrin subunit bind extracellularly? | To fibronection and laminin molecules with the underlying basal lamina. |
| How does the beta integrin subunit bind intracellularly? | Integrins bind to actin microfilaments by first binding with talin which binds to vinculin which then binds to the actin filament via alpha actinin. |
| List three apical cell membrane specializations that involve membrane evagination/ Extension | Cilia, stereocilia and microvilli |
| How do these three differ structurally? | Cilia-internal architecture of 9 peripheral microtuble doublets and two singlets centrally (for motility) Microvilli-random arrangement actin microfilaments running long(for contractility)Stereocilia-actin microfilaments,tall as cilia,commonly branch. |
| What is the function of each? | Cilia produce a coordinated wave-like movement that facilitates movement of materials over the surface of the cells. Microvilli increase surface area of the cell for absorption. Stereocilia are NOT motile so act as tall microvilli,involved in absorption |
| List three other structures associated with the apical domain of epithelial cells that are not evaginations of cell membrane | Endocytotic vesicles, glycocalyx and ion pumps/exchangers |
| What structure anchors each cilium? | A basal body. |
| To what other cellular structure is the cilia anchor similar? | The centriole |
| What type of basolateral junctions are commonly found between epithelial cells? | Zonula occludens, zonula adherens, macula adherens (desmosomes) and gap junctions (communicating junction/nexus) |
| What are two major classes of cell adhesions molecules and give an example of each | Calcium dependent and calcium independent adhesion molecules. Cadherins are an example of calcium dependent molecules while integrins are examples of calcium independent molecules. |
| List the components of the junctional complex of epithelia in order from the lumen down. | Tight junction (zonula occludens), zonula adherens, and desmosome (macula aderens). |
| How is each component constructed? Tight junctions Zonula Aderens Desmosomes | - linear regions of adjacent cell membrane, fuse,associate w/ actin microfilaments - band regions, exhibit cell mem thickening, associate w/ terminal web cytoskeleton - spot regions,exhibit cell mem thickening,associate w/ intermediate filaments |
| What is the function of each component? Tight junctions Zonula Aderens Desmosomes | -occlude intercellular space to prevent migration of foreign particles b/w cells -band-like regions specialized for adherence of one cell to its adjacent neighbours -spot-like regions specialized for adherence of one cell to its adjacent neighbour |
| How do the paracellular and transcellular pathways differ? | The paracellular pathway refers to movement of fluid or molecules down the intercellular space between epithelial cells. Transcellular pathway refers to movment through the cell itself - having to cross the apical and basal membranes. |
| Tight junctions interact/attach to which component of the cytoskeleton of the cell? | Actin microfilaments |
| What are the function(s) of the zonula occludens proteins and afadin? | They couple/link the transmembrane proteins occludin and claudin to the actin microfilaments. Afadin does the same for nectin molecules of the intercellular space also associated with tight junctions. |
| Which transmembrane proteins cross the intercellular space to meet one another, sealing off this space? | Occludin, claudin, nectin and other assorted JAMs (junctional adhesion molecules). |
| How do zonula adherens differ structurally/molecularly from macula adherens? | ZA-associated w/ actin microfilaments of cell cytosketon, require catenin or afadin-nectin complex to link desmoplakin plaque of structure to cytoskeleton D-associated w/ intermediate filaments of cell cytoskeleton, do not require a link |
| What structural and molecular features do zonula adherens share with macula adherens? | Both utilize a membrane plaque composed primarily of desmoplakin and cadherins spanning the intercellular space to link the two plaques. |
| Why is the intercellular space between zonula and macula adherens wider than normal? | Due to the large glycosylated proteins (cadherins) that span the intercellular space to link the adjacent plaques and function in adherence. |
| What is the only cell-to-cell junction specialized for cell communication? | The gap, or communicating, junction (nexus |
| Describe the structural organization of a gap junction | 6 connexin protein units assemble to form a hollow cylinder called connexon The lumen of the connexon can expand/contract up to 2 nanometers in diameter. Adjacent connexons span the intercellular space facilitating passage of molecules/electricalimpulse |
| Which specializations are found only on the basal aspect of the cells? | Hemidesmosomes. |
| With what do they attach? | The underlying basal lamina. |
| Describe the structural organization of a hemidesmosome | It is composed of an inner cytoplasmic plate and an outer non-desmoplakin-containing membrane plaque |
| Which component of the cytoskeleton is associated with a hemidesmosome? | The inner cytoplasmic plate is directly associated with tonofibrils of the cell cytoskelton |
| How does the hemidesmosome attach to the basal lamina? | Via integrins and laminin 5 anchoring filaments. |
| What is the function of basolateral membrane infolding? | They assist in linking the cell into the basement membrane/basal lamina by interdigitating - like pieces of a jigsaw puzzle. |
| What are the two main types of epithelial glands? How do they differ? | Exocrine- retain a connection to the surface (duct) by which they empty their secretions. Endocrine- do not retain the duct , become dettached from overlying epithelium from which they were derived, secrete their materials into surrounding blood vessels |
| What 3 features are used to classify epithelial glands? | Shape of secretory unit, Type of secretion, and Mode of secretory release. |
| What are the two main types of secretion? | Serous (watery) and mucous (thick, viscous). |
| How do mucous-secreting cells differ structurally from serous secreting cells? | Mucoussecreting cells have basally-flattened nucleus nucleus of seroussecreting cells is spherical, basally located, typically apical region of mucoussecreting cells does not stain as mucous has been dissolved unless a specific mucous fixative/stain use |
| List the 4 types of secretory release modes, how they work, and an example of each Merocrine Aprocine Holocrine Cytogenous | M: granules released alone, pancreatic acinar cells A: apical portion released w/ secretory granules,mammary gland H: whole cell dies, filled w/ secretory granules, sebaceous glands of hair follicle C: living cells released, sperm,egg |
| How do simple glands differ from compound | Simple epithelial glands have short, unbranched ducts that drain tubular or alveolarshaped secretory units (acini). Compound glands have extensively branching ductwork draining an elaborate acinar system. |
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wiechartm
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