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Flashcards in Epithelial specializations and exocrine glands Deck (56):
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Regional domains of epithelial cells

Apical, basal, lateral

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Apical domain

Demonstrates structural specifications. Most apical layer of cells is used to classify cell morphology.

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3 modifications to apical cell surface

1. Microvilli 2. Stereocilia 3. Cilia

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Microvilli

Small finger-like extensions of the apical membrane that project into a lumin and possess a core of actin filaments. Anchored into terminal web. Increase the surface area of the cell. Have bilayer of plasma membrane, glycocalyx (fuzzy coat).

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Stereocilia

Long non-motile microvilli which may be branched. Simular to microvilli (cylindrical projections of the apical plasma membrane which contain an actin core) but longer and may be branched. Increase apical surface area. Function in signal generation (ex. in the ear)

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Terminal web

Apical array of cytoskeletal filaments and accessory proteins where microvilli are anchored and supported

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Cilia

Hair-like projections of the apical cell surface. Much larger than microvilli. Microtubule core called the axoneme composed of tubulin dimers. Easily distinguished from microvilli by their large size and the "9+2" (9 peripheral doublets and 2 center singlets) arrangement of microtubules. Motile-using dynein (ATPase), microtubles slide past each other causing cilium to bend. Move substances across surface of an epithelial layer (ex. respiratory tract uses cilia to move mucus)

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Flagella

Contain same microtubule core (9+2 axenome) as cilia. Usually fewer in number and longer than cilia. In humans only found in spermatozoa.

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Basal bodies

Where cilia are anchored. Composed of 9 microtubule triplets (structurally the same as centrioles)

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Primary ciliary dyskinesia

Immotile cilia syndrome. Group of hereditary disorders including Kartagener's syndrome and Youngs's syndrome.

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Kartagener's syndrome

Cilia lack dynein arms resulting in chronic respiratory distress due to impaired mucus transport, male infertility

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Youngs's syndrome

Cilia have malformed radial spokes and dynein arms producing thick mucus secretions, persistent sinusitis, and reduced male fertility or sterility

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3 types of terminal bars

Zonula occludens (tight junctions), zonula adherens (adhering junctions), macula adherens (desmosomes)

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Terminal bars

Junctional complexes between adjacent cells

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Zonula occludens structure

Tight junctions. Belt-like (encircle the circumference of the cell) structures located close to the apical surface. Characterized by system of membrane folds in which outer leaflets of adjacent plasma membranes brought in close contact. Mediated by occludins in association with cadherins.

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Zonula occludens functions (2)

1. Prevent free flow of water soluble molecules between cells (apical basal) 2. Compartmentalizes integral membrane proteins into apical and basolateral domains

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Occludins

Integral plasma membrane protein that mediates zonula occludens along with cadherins

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Cadherins

Integral plasma membrane protein that mediates zonula occludens along with occludins

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Zonula adherins structure

Adhering junctions. Belt-like structures located adjacent and basal to the zonula occludens. Characterized by uniform distance between adjacent plasma membranes. Mediated by cadherins which interact with catenins that are linked to actin.

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Zonula adherins functions (2)

1. Cell adhesion 2. Link actin cytoskeletons of adjacent cells (anchor points)

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Catenins

Interact with cadherins and actin in zonula adherins

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Macula adherens structure

Desmosomes. Located basal to the belt junctions and distributed randomly along lateral membrane. Characterized by paired thickened membrane regions called attachment plaques (containing proteins like desmoplakins and pakoglobins), dense band (desmoglein) in intercellular space, site of intermediate filament cytokeratin insertion

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Macula adherens function

Strong spot adhesions between cells (like spot welds)

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Gap junctions structure

Located randomly along lateral membranes. Comprised of packed connexons (proteins composed of integral membrane proteins called connexins). Characterized by paired plaques of connexons on adjacent cell membranes and a narrow intercellular cleft.

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Gap junctions function

Provide rapid exchange of water, ions, and small molecules between adjacent cells. They are non-specific so regulate by size.

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Clostridium perfringes

Bacterial pathogen which produces a toxin that binds to claudin proteins preventing incorporation into tight junctions. This causes junctional breakdown. Diarrhea, abdominal pain.

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Heliobacter pylori

Bacterial pathogen which binds to extracellular domains of zonula occludens proteins and translocates one of its own proteins into epithelial cells. This interferes with ZO-1 protein function and causes cytoskeletal rearrangements and junction failure. May lead to gastric ulcers.

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Dust mites

Parasitic pathogen from fecal pellets the contain peptidases that cleave occluding and ZO-1 proteins. If fecal pellets inhaled tight junctions in the respiratory system break down and expose lungs to allergens. Leads to asthma attacks.

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3 basal specializations

1. Hemidesmosomes 2. Basal membrane infoldings 3. Basal lamina

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Hemidesmosomes

Junctions that attach basal cell membrane to basal lamina. Like desmosomes, site of keratin tonofilament (intermediate filament) attachment. Linkage to basal lamina is through integrins which link the ell cytoskeleton to ECM providing adhesion, traction, and bidirectional signaling.

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Integrins

Link hemidesmosomes to the basal lamina

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Basal membrane infoldings

Increase available surface area for transport (ex. Kidney)

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Basal lamina

All epithelial sheets rest on basal lamina. Two layers of epithelial cells: 1. lamina lucida-an electron lucent layer directly below basal membrane 2. lamina densa-electron dense layer directly beneath lamina lucida

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Basal lamina functions (2)

1. Provides support and attachment for epithelial sheet 2. Acts as molecular sieve or filter

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Gland definition

Cell, group of cells, or organ that produces a secretion

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Two main types of glands

1. Endocrine-secrete substances or hormones directly into the blood or lymph 2. Exocrine-secrete substances via a duct

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How are glands made?

Develop from infoldings of epithelial sheets that penetrate underlying connective tissue

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Endocrine gland

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

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Exocrine glands

Retain connection to the surface they originated from and consequently secrete product via duct or duct system

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Cellular vs. multicellular glands

Most endocrine ducts multicellular, but isolated secretory cells within an epithelium can be unicellular exocrine glands. They secrete their product apically onto the epithelial sheet.

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2 criteria for classifying multicellular glands

1. Complexity of the duct system (simple or compound) 2. Morphology of secretory proteins-tubular (straight, branched, or coiled), acinar, tubuloacinar

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Simple multicellular exocrine glands

One duct (can be straight, branched, or coiled) that opens onto the surface of the epithelial sheet

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Compound multicellular exocrine glands

Will be classified as "compound, tubuloacinar glands." Organs that have a connective tissue capsule, divided into lobes and lobules and have a complex, differetiated duct system. Small ducts-->larger ducts-->main excretory duct(s)-->surface of epithelium.

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Parenchyma

Ducts and secretory portions

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Stroma

Connective tissue components that surround and support parenchymal tissue

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Acininus

Round clusters of epithelial cells

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Intralobular duct

Inside a lobule, secretion from acinus and drains into the interlobular ducts

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Interlobular duct

Ducts between lobules, where the intralobular duct drains

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2 cell populations in secretory regions of exocrine glands

1. Secretory cells 2. Myoepithelial cells

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2 types of secretory cells

1. Mucous-secrete mucinogens (large glycosylated proteins) 2. Serous-secrete solution of protein

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Myoepithelial cells

Within the basal lamina surround the acinus. Have contractile function which aids in moving secretions out of glands.

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Invasive (inflitrating) ductal carcinoma

Mammary gland duct cells undergo 2 sequential processes: 1. Uncontrolled proliferation 2. Invasion/colonization of stroma

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5 factors controlling normal cell proliferation

1. Rate of cell proliferation=rate of cell death (rate depends on tissue) 2. Presence of committed transit amplifying daughter cells: get overall increase in number 3. Regulation of signaling pathways 4. Regulation of integrin signaling (bidirectional between cell and environment) 5. Hormone levels in mammory glands (estrogen and progesterone)

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What 4 things are carcinoma cell proliferation is affected by?

1. Genetic mutations 2. Gene duplications 3. Incorrect signaling 4. Hormonal status **One or more of these may precipitate uncontrolled epithelial cell proliferation and result in tumor formation**

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What times in development are are estrogen and progesterone regulating cell proliferation?

1. Initial development at puberty 2. Minor cyclic changes during menstual cycle 3. Development during pregnancy (also affected by prolactin) 4. Apoptosis after weaning 5. Involution (shrinkage or organs) after menopause

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What does it mean to say cancer cells are invasive?

Cells have increased migratory capacity and ability to move through or destroy the basal lamina resulting in colonization of adjacent tissues (often connective tissue) and may provide access to blood and/or lymphatic vessels with which to spread (metastasize)