Epithelial Tissue and Glands 8-29 Flashcards Preview

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Flashcards in Epithelial Tissue and Glands 8-29 Deck (94)
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4 tissue types

Epithelial, connective, muscular, nervous - extracellular material typically created by these cells.

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Epithelial tissue categories

Covering/Lining, Glandular epithelium

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Epithelial tissue functions

Secretion - glands (stomach columnar epithelium, goblet)
Absorption - intestines
Filtration
Excretion
Transport - cilia can move mucous.
Protection - epidermis - skin is an example, transitional epithelium protects urinary gland so that urine doesn't go backwards.

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Epithelial tissue characteristics

Cellularity - lots of cells in tissue bonded closely. Bound by adhesion molecules, form specialized cell junctions.
Specialized Contacts - transport outside and inside.
Polarity - free apical surface to external environment (lumen, etc.) modifications exist here, basal surface
-free or apical surface/pole/domain
-lateral surface/domain - cells in close contact (see junctions here)
-basal surface/pole/domain - epithelium comes in close contact with connective tissue.
Supported by Connective Tissue – lamina propria:
Avascular, but Innervated - connective tissue has blood vessels to supply.
Regeneration

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Cell layer types

1. Simple
2) Stratified
3) Pseudostratified - simple but look stratified (nuclei are the tell)

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Cell shapes

Squamous, cuboidal, columnar - taller than wide, elongated nucleus toward basal side usually - mostly non-ciliated form
.

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Additional cell names

Based on specialization on apical cell surface (ciliated) or apical tissue surface (keratinized)

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Urothelium

Transitional epithelium - surface cells are umbrella cells. When organ is empty (urinary bladder, ureters, urethra), wall is not distended. Wall stretches as organ fills, surface cells change shape (umbrella to squamous).

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Two Types of Stratified Squamous Epithelium

Nonkeratinized Stratified Squamous Epithelium
Keratinized Stratified Squamous Epithelium

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Domains of epithelial cells

Apical domain
Lateral domain
Basal domain

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Microvilli

Cytoplasmic extension/processes with core of actin filaments. 1 microm high, Average width: 0.08µm
Creating striated border (intestinal epithelium) or brush border (kidney tubule cells)
Function: increase surface area

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Stereocilia

Considered long microvilli
Function: increase surface area

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Cilia

movement, rapid back and forth motion. 5-10 microm in length, 0.2 microm in width. Contains an axoneme, The microtubules insert into basal bodies

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Junctional complex parts

Zonula Occludens or Tight Junctions
Zonula Adherens
Macula Adherens or Desmosomes

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Zonula occludens

Tight junction - type of occluding junction
found closest to apical surface
transmembrane proteins (occludins and claudins) fuse outer surfaces of adjacent membranes together sealing off the intercellular space
forms a continuous band around the cell which is impermeable, thus it limits the movement of substances between luminal space and tissue compartments via the intercellular space
diffusion barrier between cells
gives the “barrier” characteristic to epithelial tissue; for items to get across now they must be actively transported via the specialized membrane proteins of epithelial cells
also prevents integral membrane proteins movement between domains
provide only limited resistance to mechanical stresses

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Zonula adherens

a type of anchoring junction
provide mechanical stability by linking cytoskeleton of one cell to the cytoskeleton of the next; great for resisting separation
forms a continuous band around the cell
microfilaments (actin) of the first cell attach to a plaque on the inside of its plasma membrane; this plaque is attached to transmembrane protein (cadherin) which crosses the plasma membrane of the first cell and attaches to the cadherin of an adjacent cell; this second cell’s cadherin crosses its plasma membrane where it attaches to a plaque just on the inside of the plasma membrane; this plaque is attached to the microfilaments (actin) of the second cell; thus connecting cytoskeleton of one cell to the next.

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Macula adherens

Desmosome - a type of anchoring junction
provide mechanical stability by linking cytoskeleton of one cell to the cytoskeleton of the next; great for resisting separation
forms spot welds; not continuous around cell; localized
intermediate filaments of the first cell attach to a plaque on the inside of its plasma membrane; this plaque is attached to transmembrane protein (cadherin) which crosses the plasma membrane of the first cell and attaches to the cadherin of an adjacent cell; this second cell’s cadherin crosses its plasma membrane where it attaches to a plaque just on the inside of the plasma membrane; this plaque is attached to the intermediate filaments of the second cell; thus connecting cytoskeleton of one cell to the next.

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Gap junctions

these are communicating junctions
transmembrane proteins are in the form of a protein tunnel called a connexon
the connexon of one cell lines up with the connexon of the next cell allowing the cells to exchange ions and small molecules; these items can diffuse from the cytosol of one cell to the cytosol of the next.
allows communication between cells; this is especially important in tissues were the activity of the cells need to be coordinated.

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Basal lamina components

Lamina lucida, lamina densa

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Focal Adhesions

a type of anchoring junction
looks somewhat similar to a zonula adherens junction, but it doesn’t link adjacent cells
links the cell to the basal lamina; specifically it anchors microfilaments (actin) of the cytoskeleton of a cell to the basal lamina
actin filaments are attached to extracellular matrix glycoproteins (ex. laminin and fibronectin) in the basal lamina via integrins (the transmembrane protein used here)
functional role in signal detection and transmitting signals from the extracellular environment into the interior of the cell; mechanosensitivity

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Hemidesmosome

a type of anchoring junction
looks somewhat similar to a desmosome, but it doesn’t link adjacent cells
links the cell to the basal lamina; specifically it anchors intermediate filaments of the cytoskeleton to the basal lamina
intermediate filaments are attached to laminin and type IV collagen in the basal lamina via integrins (the transmembrane protein used here)
found in epithelia subject to abrasion and mechanical shearing forces; useful for keeping the epithelium from separating from the underlying connective tissue

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Gland types

Relation to surface - endocrine and exocrine

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Endocrine gland

ductless glands; secrete into interstitial fluid, release hormones

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Exocrine gland

secrete their products onto a surface either directly or via an epithelial duct.

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Endocrine gland hormones

Circulatory Hormones
Paracrine Hormones
Autocrine Hormones

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Exocrine gland classificating traits

Cellularity
Structure/Morphology
Type of Secretion
Mode/Mechanism of Secretion

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Cellularity (exocrine)

can be classified based on the number of cells that compose the gland - Unicellular Exocrine Glands – one cell
Multicellular Exocrine Glands – more than one cell; consists of a cluster of cells.

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Goblet cells

Intestinal epithelium - produce and secrete mucin - also in epithelial lining of respiratory tract. Nucleus like a wine glass (almost triangular).

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Structure/morphology exocrine

Structure of Duct
Simple – unbranched
Compound – two or more branches
Structure of Secretory Units*
Tubular – tube shaped; either short or long and coiled
Alveolar or Acinar – round or globular
Tubuloalveolar and Tubuloacinar – combination

*Note: These secretory units can be branched or unbranched; they also may be coiled.

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Simple duct structure

Duct does not branch

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Compound duct structure

Duct branches

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Secretion - exocrine

Mucous Glands
Serous Glands
Mixed Glands

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Serous cells

Polarized, protein-secreting cells
Typically produce digestive enzymes and other proteins
Pyramidal in shape – broad base on basal lamina and narrow apical surface facing lumen
Contain secretory granules called zymogen granules – spherical in shape; found in apical cytoplasm
Basophilic cytoplasm due to RER and free ribosomes
Nuclei are rounded

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Mucous cells

Produce hydrophilic glycoprotein mucins
Cuboidal or columnar in shape
Flattened nuclei at base of cells
Contain secretory granules called mucinogen granules – found in apical cytoplasm; PAS positive

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Myoepithelial cells

Found within the basal lamina of secretory units and the initial part of duct system
Can contract; accelerates secretion of the product
Also prevent distention of area when lumen fills

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Salivon

Basic unit of salivary gland. composed of the acinus and all related ducts.

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Acinus

is a blind sac composed of secretory cells and is the secretory portion. Three secretory acini are found in salivary glands

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3 acini in salivary glands

Serous Acini, Mucous Acini Mixed Acini

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Serous acini

serous cells only; generally spherical shaped

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Mucous acini

mucous cells only; generally tubular shaped

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Mixed acini

contain both serous and mucous cells; in traditional fixation methods it appears the mucous acini have a cap of serous cells; these caps are called serous demilunes; found in the sublingual and submandibular glands

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Serous demilunes

Cap of serous cells on mucous acini.

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Types of exocrine glands based on secretion mode

Merocrine Glands
Holocrine Glands
Apocrine Glands

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Muscular tissue

moderate amount of EC matrix

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Nervous tissue

Detect stimuli, react via action potentials. Lots of cells with intertwining processes, little to no EC material.

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lamina propria

Connective tissue associated with mucous membranes (wet).

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Basement membrane

Secreted by epithelial tissue and includes connective tissue below.

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Naming for stratified epithelium

Look at surface cells only.

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Umbrella cells

Transitional epithelium - top layer "squishy" non-distended = rounded shape.

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Naming *Squamous

Keratinized or nonkeratinized - skin is where you see keratinized most. Nonkeratinized shows up in esophagus, vagina.

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Columnar Naming

Ciliated, nonciliated. Most simple columnar is non-ciliated. See most of this in stomach, small intestine and large intestine. Since most is non-ciliated, nonciliated term usually dropped.

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Pseudostratified naming

Almost all have cilia.

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Simple protection

Most do not offer protection, usually there for exchange (especially squamous).

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Serous membrane

Covers peritoneal cavity/organs

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Bowman's Capsule

Simple squamous - nuclei bulge.

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2 places where simple squamous changes names

Mesothelial lining of peritoneum Mesothelium. Endothelium - lines arterioles and heart.

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Mesothelium

simple squamous membrane associated with thoracic cavity **check this**

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Endothelium

Simple squamous associated with blood vessels/lining heart. Cells in the direction of bloodflow (reduce resistance within blood vessels).

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Simple cuboidal

Secretion, absorption, infiltration, excretion. Kidney tubules, ducts (a lot are with this), small glands, ovary surface.

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Simple columnar

Goblet cells in these tissues, absorption, secretion of mucous, produce enzymes/substances. Some are ciliated to propel mucous or reproductive cell ciliary action. Most of the digestive tract is this. Ciliated columnar line bronchi. **NOTE distinguish between microvilli and cilia. Microvilli are much shorter.

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Duct cell type

Change as ducts go out - some have simple columnar to stratified.

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Slide 26

*

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Stratified squamous

If you see nuclei at surface (alive), nonkeratinized.

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Stratified cuboidal

Very rare - find in sweat glands, a few esophogeal glands, part of male urethra, etc.

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Stratified columnar

Taller than wide, very rare. Lines part of urethra, large excretory ducts, etc.

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Pseudostratified columnar

Goblet cells usually associated with it, can be associated with cilia (usually is). Find this lining the majority of the respiratory tract. Respiratory epithelium = ciliated pseudostratified columnar epithelium.

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Trachea

has thickest basement membrane of whole body.

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Slide 34

View slide images

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Review all scope slides

**

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Polarity

Surface and organelle location - cellular junctions keep certain membrane proteins on one surface.

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Striated border

Layer of microvilli creating striated border. Intestines.

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Brush border

Striated border in kidney.

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Microvilli

20-30 actin filaments cross linked to each other. Ties into terminal web (more actin filaments) to secure it. Myosin helps tie the actin to PM, but no movement.

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Cilia vs microvilli

Grouped and clumped and longer than microvilli. Microvilli in an even layer.

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Stereocilia

Long microvilli - Does not move. Just more surface area. In epidydimus, associated with sensory cells of inner ear. Core is the same 20-30 actin filaments into terminal web.

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Cilia

Move, longer and wider than microvilli. Respiratory tract, oviducts. Move fluid or particulate matter along apical surface. Tie in to basal bodies (darker at surface, more sporadic). Shorter than flagella

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Terminal bars

Junctional complex - no cement, represent junctional complex - numerous cell junctions.

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Zonula occludens

Goes whole way around cells. Tight junction, occluding junction. Transmembrane proteins link one cell to the next. Creates a diffusion barrier, nothing gets between cells. Must cross plasma membrane. Limits movement of transmembrane proteins in plasma membrane as well. Sets PM domains, not good for mechanical resistance.

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Zonula

Wrapping whole way around a cell. Ties cytoskeleton (actin) of once cell to another.

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Macula adherens

Intermediate filaments tie to plaques this time (see 3)

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Connexon

Transmembrane protein (6 connexins). Connexon of 1 cell lines up with the connexon of the next. Connexins change shape to open or close a channel. Connects cytosol to cytosol.

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Basement membrane

Basal lamina and reticular lamina. Only with LM

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PAS Stain

Periodic acid schiff stain. Looks for sugars, shows basement membrane. Breaks down glycogen

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Basal lamina

Lamina lucida (transparent artifact), lamina densa. Using osmium tetroxide you can see this. Use this term for EM.

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Glandular epithelium

Proliferation of cells into connective tissue. Cells can synth, store, release complexes. Often store product in secretory granules.

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Endocrine

Stuff picked up from EC to cardiovascular system (thyroid, pituitary, adrenal)

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Circulatory

Picked up by cardiovascular system. Only cells w/receptors can respond. Extremely common.

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Paracrine

Interstitial fluid, binds to adjacent cells.

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Autocrine

Binds to self to affect activity.

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Goblet

Unicellular exocrine gland.

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Conventional fixation **amend**

Mucogen granules pass serous cells out**

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Merocrine

Exocytosis - most common form of secretion

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Holocrine

Rupture - sevaceous glands of skin

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Apocrine

Cytoplasm, PM, product. Debatable if in humans. Basically cell losing it's top. Closest example is mammary glands... but no cytoplasm.