Epithelia Flashcards
Tissues
A layer or group of cells that collectively perform a specific function ex. Smooth muscle, loose connective, nervous tissue, blood, columnar epithelium
Epithelium
Sheet of attached cells
Have polarity
No blood vessels
Basal Side
The area of the epithelium where it connects to the basement membrane (bottom)
Apical side
Side facing the free surface
Classify Epithelium based on # of cell layers
Simple Simple pseudo-stratified (1 layer, appears as multi-layered) Stratified (multi-layer) Transitional (urinary tract; large collecting duct of kidney or in the bladder)
Simple Squamous Epithelium
Single layer of cells Extremely flat
Mesothelium
Body Cavity Simple Squamous epithelium
Endothelium
Blood vessels Simple squamous epithelium
Simple Cubodial Epithelium
Single layer of cells Look like cubes Almost always found in the collecting duct of the kidney Height and width is the same
Simple Columnar Epithelium
Single layer of cells All anchor to the basement membrane Columnar in shape Usually have microvilli or cillia ex. intestine (microvilli) oviduct (cillia)
Simple Pseudo Stratified Epithelium
All cells touch the basement membrane but not all cells reach the free surface
Some are shorter and some are much taller
ex. Trachea
Stratified Squamous Epithelium
Cells tightly associated cells with eachother
Not all the cells are touching the basement membrane
ex. esophagus
ex. skin
Stratified Cubodial/Columnar Epithelium
Nearly always 2 cell layers
Found in larger excretory ducts or glands (salivary)
Based on the morphology of the top layer
Transitional Epithelium
Found in the bladder or the large collecting duct of the kidney
Adaptable, but similiar to stratified squamous
Top layer of cells may vary in shape
Shape ranges from a bulge to complete flattening
Basement Membrane (Component of Epithelia)
- Interface between epithelia and connective tissue
- Site of attachment for connective tissue
- Basal Lamina (TEM structure)
- Type IV Collagen + other proteins + carbohydrates (contain sugars)
- Synthesized- serves as a scaffold and filtration barrier
Stain used to detect Type IV Collagen
- Heidenhain’s Azan Stain
- Stains Type IV Collagen Blue in the basement membrane
Stain used to locate the basement membrane by light microscopy
- PAS Stain (Periodic Acid Schiff Stain)
- Carbohydrates (stain purple)
Hemidesmosomes
- Promote the adhesion of epithelial cells to the underlying basement membrane
- Attachment of cells to the extracellular matrix
- Maintenance of tissue structure and integrity
- Intermmediate filaments extend into the intracellular cytoplasm
- Connect a cell through a plaque to the basement membrane (ECM) via integrins (multi-protein complexes)
- TEM - dark dense signaling areas dispersed throughout basement membrane
Tight Junctions (Natural Side of the Cell)- Interior
- Closer to the apical surface
- Seal neighboring epitheal cells via a band of claudulin proteins
- Limit the passage of molecules and ions through the space
- Block the movement of integral membrane proteins
Adherens Junction
- Strong mechanical attachments between neighboring cells
- Uses cadherin- specialized transmembrane protein to adjoin neighboring cells
- Intracellularly contains actin filaments bound to anchoring proteins
- Connections are made inside the cell
Mutiple types of adherins proteins (ex. cadherin)- tissue specific
Desmosomes
- Hemidesmosome of 1 cell + hemidesmosome of a neighboring cell
- Connects the intermmediate filaments (intracellular cytoplasmic side) of both cells via a plaque and transmembrane proteins
Terminal Web
- Composed of Actin filaments
- Stabilizes a whole set of microvilli
- Dense network of F-actin
- HUGE difference between F-actin belts connecting adherens junctions on slides
Gap Junctions
- Spot junctions with pores
- 2 cells connect to eachother via channel proteins
- Allows for material exchange between neighboring cells
- ex. Bone tissues rely on these for nutrient exchange
- Intercellular exchange of ions and other molecules
Cell Junctions (Lateral Side of Epithelial Cells)
- Gap Junctions
- Tight Junctions
- Hemidesmosomes
- Desmosomes
- Adherens Junctions
Cell Surface Specializations
Microvilli
Microvilli (Apical Cell Surface Specialization)
- Cytoplasmic finger extensions - allows them to expand their apical surface
- Form a “brush border”
- Easily seen on TEM
- Each supported by an actin core
- Role = expand the surface of the cell
- Coated by glycocalyx (sugar coating)
- Underneath F-actin core –> terminal web (dense F-actin network)
- Highly organized in some tissues, but irregular in others
Centrioles (Apical Cell Surface Specialization)
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Cillia (Apical Cell Surface Specialization)
- Microtubule based structure
- Can assist in moving things outside of the cell
- “beat”- wavelike action
- Found in the lining of the respiratory tract & female reproductive tract
- Move mucus (secreted by goblet cells) and particles across epithelial cells
Specialized Epithelium (Glands)
- Endocrine
- Exocrine
Endocrine Glands (Specialized Epithelium)
- Secrete hormones directly into the bloodstream
- Glands without ducts
- Secretory epithelial cells
- Tightly controlled secretions
- ex. Insulin secretion
Exocrine Glands (Specialized Epithelial Cells)
- All are glands with ducts
- Unicellular (Goblet cells) or multi-cellular
- Secretions are delivered into ducts, that end up on the apical epithelial surface
- Ex. salivary
- Constant secretion- not tightly controlled
Muticellular Gland Structure (Specialized Epithelium)
- Simple tubular
- Simple coiled tubular
- Simple branched tubular
- Simple acinar
- Simple branched acinar
- Compound branched tubular
- Compound acinar
- Compound tubulo-acinar
Acinus is different from a tubule
Acinus is at the END of a tubulue & is a balooning out, hollow, ball-like structure
Organization of Compound Glands
- Lobes and lobules (areas separated by connective tissue)
- Duct = the tubulue connecting the gland to the epithelial surface
- Adenomeres (several acini) = functional units
- Acinus = group of secretory cells
Lobules are inside lobes
Adenomeres are inside lobules- connected by a collecting duct
Cells that facilitate the secretions of glands
Myoepithelial Cells
- Cover the acini
- Contract and expel
- Squeeze acini
Acini Classifications Based on Material Secreted
- Serous Acinus= protein + H2o
- Mixed Acinus = protein + sugar
- Mucous Acinus = mucous
Serous Acinus–> darker cytoplasmic staining on an H&E Stain than other secretions
Classification of Glands by Mode of Secretion
EXOCRINE GLANDS ONLY
- Apocrine
- Merocrine
- Holocrine
Apocrine Secretion
- Apical portion of the cell’s cytoplasm + secretory product is pinched off
- Released into extra-cellular space
- After secretion = cells lose large chunk of cytoplasm
- Apical surface before secretion = flat
- Post-secretion - apical surface of secretory cells have a pyramidal or triangular shape
ex. Sweat glands, Ceruminous glands (ear wax)
Merocrine Secretion
- No breakdown of cellular material during secretion
- Exocytosis mechanism
- Membrane of secretory vesicles fuses with plasma membrane
- Contents of vesicles are released into extracellular space
- ex. Salviary gland
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Holocrine Secretion
- Entire cell disintegrates to discharge it’s secretion into collecting duct
- Results in cell death
- Complete loss of cytoplasm
- ex. Sebaceous gland releases lipid to hair follicle
Serous Gland Secreted Product
Protein + Water
Pink dots appear on Eosin staining
Mucous Glands (Secreted Product)
Secrete viscous solution of glycoproteins & polysaccharides
Washed out appearance on H&E stain
Mixed Gland (Secreted Product)
Serous & Mucous Secretion
Lipid Glands
Breast (milk)
Sebaceous Gland
What kind of glands does the pancreas have?
The pancreas has exocrine regions that make digestive enzymes, and endocrine regions (Islets of Langerhans) that make stuff like insulin, glucagon, etc.
Epithelium
Histological layer that lines structures and interfaces with the adjacent environment
Varying surface of pseudostratified epithelial cells
Any cell with a polarity has an apical vs. basolateral surface
In pseudostratified epithelium, the basolateal aspect always contacts the basement membrane. BUT, some cells may also reach the surface, and thus the apical surface will be there.
Other cells may NOT reach the surface, In that case, the apical surface will be “stuck” in the middle of the layer.
All cells might not reach the lumen but each cell would have an apical surface
