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Flashcards in Epithelial specializations and exocrine glands Deck (77):
1

4 characteristics of epithelial tissue

1. Contiguous sheets of cells (more cells than ECM) joined by junctions 2. Polarity 3. Rest on/attached to basal lamina 4. Avascular (receive nutrients via blood vessels)

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2 components of tissues

1. Cells 2. Extracellular matrix (ECM)

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Extracellular matrix (ECM)

Region outside cells including complex of macromolecules produced by cells and exported into extracellular space (dissolved substances and fibers)

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4 functions of epithelial tissue

1. Covering/protection 2. Absorption/secretion (transcellular transport, absorb liquids and gas, secrete mucus, enzymes, hormones) 3. Barrier (compartmentalize) 4. Sensory

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2 ways to classify epithelia

1. Number of layers 2. Morphology of apical layer

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3 morphologies of epithelia

1. Squamous 2. Cuboidal 3. Columnar

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2 main categories of layers of epithelia

1. Simple (one layer) 2. Stratified (multiple layers) which are always classified by the apical cell layer

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Pseudostratified ciliated columnar epithelia

Specialized epithelia where all cells in contact with basal lamina, but not all reach the apical surface of the epithlium. Nuclei appear as 2-3 layers. Usually columnar and have ciliated cells.

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Transitional epithelia

Several layers (polyhedral shaped) with most cells in apical layer being dome shaped (relaxed) and some flattened (distended). Variable morphology throughout layers.

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Keratinized layers

Seen in stratified squamous epithelium (like skin). Should be classified as "stratified squamous, keratinized (or non-keratinized)"

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Which epithelial layer determines structural specializations and morphology?

Apical layer

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Microvilli

Small, finger like extensions of apical membrane that project into lumen and have actin filament core and fuzzy coat (glycocalyx). Anchored into the terminal web. Increase surface area and form a brush border.

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Glycocalyx

Fuzzy coat found on microvilli seen in cross-section

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Terminal web

Apical array of cytoskeletal filaments where microvilli or stereomicrovilli are anchored

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Stereocilia

Long, non-motile microvilli which may be branched. Anchored into the terminal web. Increase apical surface area and function in signal generation.

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Cilia

Hair-like motile projections of apical cell surface anchored via basal bodies and much larger than microvilli. Contain a microtubule core of tubulin dimers which make the axoneme (9+2 arrangement). Associate with dynein ATPase.

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Flagella

Same 9+2 microtubule core as cilia and only found in spermatozoa

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Basal bodies

Anchor cilia and contain 9 microtubular triplets (just like centrioles)

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Anoneme

9+2 microtubule core (9 peripheral doublets with dynein arms and 2 center singlets) made up of tubulin dimers found in cilia

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Tubulin

Dimerize to make microtubules which form axonemes in cilia

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Primary cilia dyskinesia

AKA mmotile cilia syndrome. Group of hereditary disorders including Kartagener's syndrome and Young's syndrome.

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Kartagener's syndrome

Cilia lack dynein arms which cause chronic respiratory disease due to lack of mucus transport and male sterility

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Young's syndrome

Cilia have malformed radial spokes and dynein arms which make very thick mucous secretions causing persistent sinusitis and reduced fertility/sterility

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Terminal bars

Junctional complexes (all 3 types of junctions together) that are visible at the light microscope level

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Zonula occludens

AKA tight junctions. Belt-like structures close to apical surface. Mediated by occludens and claudins in association with cadherins.

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Occludens

Mediate zonula occludens with claudens

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Claudens

Mediate zonula occludens with occludens

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Cadherins

Associate with occludens, claudins to mediate zonula occludens and associate with catenins to mediate zonula adherens

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Zonula adherens

AKA adhering junctions. Belt-junctions which are adjacent and below zonula occludens. Mediated by catenins which are linked to actin. Anchor actin filaments for cell adhesion.

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Catenins

Mediate zonula adherens and link to actin

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Macula adherens

AKA desmosomes. Below belt junctions and randomly distributed along lateral membrane. Have attachment plaques (contain desmoplakins and pakoglobins) and associate with cytokeratin. Spot welds between cells.

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Attachment plaques

Found in macula adherens and include desmoplakins and pakoglobins

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Desmoplakins

Attachment plaque protein in macula adherens

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Pakoglobins

Attachment plaque protein in macula adherens

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Cytokeratin

Intermediate filaments which associate with macula adherens and insert themselves at the cytoplasmic face

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Gap junctions

AKA communicating junctions. Rapid exchange of small molecules between adjacent epithelial cells. Located randomly along lateral membranes. Comprised of paired packed connexons which are formed by connexins) which form aqueous core. Regulated by intracellular levels of Ca2+ and pH.

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Connexons

Formed by connexins and make up gap junctions

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Connexins

Integral membrane proteins which form connexons

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Clostridium perfringens

Bacterial pathogen in gut which produces toxin that binds to claudin proteins and prevent their incorporation into tight junctions. Tight junctions break down. Diarrhea, abdominal pain.

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Heliobacter pylori

Binds to extracellular domain of zonula occludins and inserts its' own protein into epithelial cells interfering with ZO function causing cytoskeleton rearrangements and junction failure. Gastric ulcers.

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Dust mites

Parasitic pathogen (fecal pellets) containing peptidases that cleave occluding ZO proteins. If inhaled cause respiratory epithelium breakdown and expose lungs to inhaled allergens. Asthma attacks.

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Hemidesmosomes

Junctions that attach basal cell membrane to basal lamina. Site of keratin tonofilament attachment. Linkage to basal lamina is through integrins which link cytoskeleton to ECM for adhesion, traction, and signaling.

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Keratin tonofilaments

Intermediate filaments which attach to hemidesmosome

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Integrins

In hemidesmosomes link cell cytoskeleton to ECM

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Basal membrane infoldings

Multiple invaginations of basal plasma membrane to increase surface area for transport. Many mitochondria are present.

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Basal lamina

Acellular structure produced by epithelia where epithelial sheets rest. 2 layers include lamina lucida and lamina densa. Can only be observed at electron microscopic level.

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2 functions of basal lamina

1. Support/attachment for epithelial sheet 2. Molecular sieve/filter

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Lamina lucida (rara)

Electron lucent layer directly below basal membrane

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Lamina densa

Electron dense layer directly beneath lamina lucida

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Basement membrane

Includes 2 layers of the basal lamina + a third layer called the lamina reticularis (produced by connective tissue cells)

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Exocrine glands

Retain connection to surface they originated from and secrete product via ducts or duct systems.

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Endocrine glands

Lose connection to epithelial surface of origin. Ductless and secrete products into blood or lymphatic vessels.

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2 main types of glands

1. Endocrine: secrete substances or hormones directly into blood/lymph 2. Exocrine: secrete substances via ducts Both develop from infoldings of epithelial sheets that penetrate into underlying connective tissue.

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Classification of exocrine glands

Unicellular (goblet cells in respiratory and digestive tracts) or multicellular (sweat glands, sebaceous glands in scalp, gastric glands in stomach, salivary gland)

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Further classification of multicellular exocrine glands

1. Complexity (simple or compound) 2. Morphology (tubular, acinar, tubuloacinar)

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Simple multicellular exocrine glands

Part of an organ or tissue. One duct (can be straight, branched, or coiled) which opens to surface of epithelial sheet. Sweat glands, sebaceous glands in scalp, gastric glands in stomach.

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How will compound exocrine glands ALWAYS be classified?

Compound tubuloacinar

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Compound multicellular exocrine glands

The organ themselves. Complex, branched, differentiated duct system (small ducts to larger and larger). Parotid salivary gland, mammory gland, pancreas.

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3 morphologies of secretory portions of glands

1. Tubular 2. Acinar or alveolar 3. Tubuloacinar

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Tubular

Can be straight, branched, or coiled (tangled ball of yarn cut)

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Acinar or alveolar

Ball of cells which can be solid or have space/lumen in the center

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Tubuloacinar

Branched with acini

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Acinus

Cluster of cells organized around central lumen

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Parenchyma

Secretory portions and ducts in compound glands

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Stroma

Connective tissue components which surround/support parenchyma in compound glands

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Intralobular ducts

Will be found surrounded by acini (dark areas)

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Interlobular ducts

Will be found in connective tissue (light areas)

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2 cell populations in secretory regions

1. Secretory cells 2. Myoepithelial cells

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2 main types of secretory cells

1. Mucous 2. Serous

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Mucous cells

Secrete mucinogens (large glycosylated proteins)

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Serous cells

Secrete solutions of proteins

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Myoepithelial cells

Located surrounding groups of secretory cells within the basal lamina. Characteristics of smooth muscle cells (contractile filaments) which aids in moving secretions out of secretory portion of glands (like a hand squeezing a stress ball).

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How is the type of secretion in exocrine glands determined?

By the kind of secretory cells which predominate (serous or mucous)

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Invasive (infiltrating) ductal carcinoma (2 changes to cells)

Mammory gland duct cells undergo 1. Uncontrolled proliferation 2. Invasion/colonization of stroma

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4 factors controlling normal epithelial cell proliferation

1. Rate of proliferation = rate of apoptosis 2. Presence of committed transit amplifying daughter cells (overall increase in #) 3. Regulation by signal pathways 4. Regulation of integrin signaling (through hemidesmosomes)

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How is mammory gland proliferation normally controlled vs in carcinoma?

Normal ways + hormones estrogen and progesterone during development. In carcinoma genetic mutations, gene duplications, incorrect signaling, and hormonal status affect proliferation.

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Invasive cancerous epithelial cells

Able to move through or destroy basal lamina and colonize in adjacent tissues