Epithelial Tissue and Glands 8-29 Flashcards
4 tissue types
Epithelial, connective, muscular, nervous - extracellular material typically created by these cells.
Epithelial tissue categories
Covering/Lining, Glandular epithelium
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.
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
Cell layer types
- Simple
2) Stratified
3) Pseudostratified - simple but look stratified (nuclei are the tell)
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)
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).
Two Types of Stratified Squamous Epithelium
Nonkeratinized Stratified Squamous Epithelium
Keratinized Stratified Squamous Epithelium
Domains of epithelial cells
Apical domain
Lateral domain
Basal domain
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
Stereocilia
Considered long microvilli
Function: increase surface area
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
Junctional complex parts
Zonula Occludens or Tight Junctions
Zonula Adherens
Macula Adherens or Desmosomes
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
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.
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.
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.
Basal lamina components
Lamina lucida, lamina densa
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
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
Gland types
Relation to surface - endocrine and exocrine
Endocrine gland
ductless glands; secrete into interstitial fluid, release hormones
Exocrine gland
secrete their products onto a surface either directly or via an epithelial duct.
Endocrine gland hormones
Circulatory Hormones
Paracrine Hormones
Autocrine Hormones
Exocrine gland classificating traits
Cellularity
Structure/Morphology
Type of Secretion
Mode/Mechanism of Secretion
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.
Goblet cells
Intestinal epithelium - produce and secrete mucin - also in epithelial lining of respiratory tract. Nucleus like a wine glass (almost triangular).
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.
Simple duct structure
Duct does not branch
Compound duct structure
Duct branches
Secretion - exocrine
Mucous Glands
Serous Glands
Mixed Glands
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
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
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
Salivon
Basic unit of salivary gland. composed of the acinus and all related ducts.
Acinus
is a blind sac composed of secretory cells and is the secretory portion. Three secretory acini are found in salivary glands
3 acini in salivary glands
Serous Acini, Mucous Acini Mixed Acini
Serous acini
serous cells only; generally spherical shaped
Mucous acini
mucous cells only; generally tubular shaped
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
Serous demilunes
Cap of serous cells on mucous acini.
Types of exocrine glands based on secretion mode
Merocrine Glands
Holocrine Glands
Apocrine Glands
Muscular tissue
moderate amount of EC matrix
Nervous tissue
Detect stimuli, react via action potentials. Lots of cells with intertwining processes, little to no EC material.
lamina propria
Connective tissue associated with mucous membranes (wet).
Basement membrane
Secreted by epithelial tissue and includes connective tissue below.
Naming for stratified epithelium
Look at surface cells only.
Umbrella cells
Transitional epithelium - top layer “squishy” non-distended = rounded shape.
Naming *Squamous
Keratinized or nonkeratinized - skin is where you see keratinized most. Nonkeratinized shows up in esophagus, vagina.
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.
Pseudostratified naming
Almost all have cilia.
Simple protection
Most do not offer protection, usually there for exchange (especially squamous).
Serous membrane
Covers peritoneal cavity/organs
Bowman’s Capsule
Simple squamous - nuclei bulge.
2 places where simple squamous changes names
Mesothelial lining of peritoneum Mesothelium. Endothelium - lines arterioles and heart.
Mesothelium
simple squamous membrane associated with thoracic cavity check this
Endothelium
Simple squamous associated with blood vessels/lining heart. Cells in the direction of bloodflow (reduce resistance within blood vessels).
Simple cuboidal
Secretion, absorption, infiltration, excretion. Kidney tubules, ducts (a lot are with this), small glands, ovary surface.
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.
Duct cell type
Change as ducts go out - some have simple columnar to stratified.
Slide 26
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Stratified squamous
If you see nuclei at surface (alive), nonkeratinized.
Stratified cuboidal
Very rare - find in sweat glands, a few esophogeal glands, part of male urethra, etc.
Stratified columnar
Taller than wide, very rare. Lines part of urethra, large excretory ducts, etc.
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.
Trachea
has thickest basement membrane of whole body.
Slide 34
View slide images
Review all scope slides
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Polarity
Surface and organelle location - cellular junctions keep certain membrane proteins on one surface.
Striated border
Layer of microvilli creating striated border. Intestines.
Brush border
Striated border in kidney.
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.
Cilia vs microvilli
Grouped and clumped and longer than microvilli. Microvilli in an even layer.
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.
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
Terminal bars
Junctional complex - no cement, represent junctional complex - numerous cell junctions.
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.
Zonula
Wrapping whole way around a cell. Ties cytoskeleton (actin) of once cell to another.
Macula adherens
Intermediate filaments tie to plaques this time (see 3)
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.
Basement membrane
Basal lamina and reticular lamina. Only with LM
PAS Stain
Periodic acid schiff stain. Looks for sugars, shows basement membrane. Breaks down glycogen
Basal lamina
Lamina lucida (transparent artifact), lamina densa. Using osmium tetroxide you can see this. Use this term for EM.
Glandular epithelium
Proliferation of cells into connective tissue. Cells can synth, store, release complexes. Often store product in secretory granules.
Endocrine
Stuff picked up from EC to cardiovascular system (thyroid, pituitary, adrenal)
Circulatory
Picked up by cardiovascular system. Only cells w/receptors can respond. Extremely common.
Paracrine
Interstitial fluid, binds to adjacent cells.
Autocrine
Binds to self to affect activity.
Goblet
Unicellular exocrine gland.
Conventional fixation amend
Mucogen granules pass serous cells out**
Merocrine
Exocytosis - most common form of secretion
Holocrine
Rupture - sevaceous glands of skin
Apocrine
Cytoplasm, PM, product. Debatable if in humans. Basically cell losing it’s top. Closest example is mammary glands… but no cytoplasm.
