Histology: Epithelium Flashcards
1
Q
Define epithelial tissue.
A
-
Avascular tissue (gets oxygen/nutrient via diffusion) composed of closely aggregated cells that form sheets
- Cover internal & external body surfaces
- Form secretory portions of glands and ducts
- Sensory tissues (nasal, oral cavities, eyes)
2
Q
Functions of epithelial tissue.
A
- Protection
- Absorption
- Secretion
- Sensory reception
- Contraction
3
Q
Characteristics of epitheial tissues.
A
- Close together and adhered to one another via specialized cell junctions (junctional complexes)
-
Polarized both functionally and morphologically
- Apical domain (faces lumen)
- Basal domain (attached to basement membrane)
- Lateral domain
4
Q
Basement Membrane
A
- Attaches epithelium to connective tissue
- Forms a semipermeable “filter” to regulate exchange between epithelium and connective tissue
- Really thick in the trachea
2 Layers:
- Basal lamina (secreted by epithelial cells)
- Reticular lamina (more fibrous; secreted by CT fibroblasts)
- Type III collagen
5
Q
Structure of the basal lamina
A
- Produced by epithelial cells
- Type IV collagen (forms meshwork)
Laminins
- Glycoproteins that bind integrin receptors in cell membrane
Nidogen (glycoprotein) & Perlecan (proteoglycan)
- Cross-link laminin to type IV collagen
6
Q
Basement Membrane LM
A
- PAS stain shows BM as a line underneath epithelial cells
7
Q
Types of Junctional Complexes
A
- Tight junctions (most apical)
- Also called zonula occludens (encircling entire perimeter of cell)
- Adherent junctions
- Also called zonula adherens
- Desmosomes
- Also called macula adherens (“macula” means spot)
- Gap Junctions
- Allow cells to communicate with one another
8
Q
Tight Junctions
A
- Most apical
-
Form a seal between adjacent cells (form a barrier)
- Controls passage of molecules between cells
- Separates apical from basolateral domains
- Cells are polarized (differning functions in different domains)
Structure:
-
Occludin & Claudin
- transmembrane proteins to anchor cells together
-
Zonula Occludens Proteins
- attach to occludin and claudin
- attach to actin filaments in cytoskeleton
9
Q
Transcellular Transport
A
- Active transport system
- Allows transport across the plasma membrane
10
Q
Paracellular Pathway
A
- Between cells (prevented by tight junctions)
- Small molecules (water, electrolytes) can pass
- Claudins form aqeuous channels
11
Q
Adherens Junctions
A
- Immediately below tight junctions
- Anchors cell to adjacent cell
Structure:
-
E-cadherins
- transmembrane protein to form junction
-
Catenins
- binds e-cadherins and actin filaments inside plasma membrane
- Widening between terminal bar (dots) and terminal web (line) in LM
12
Q
Desmosomes
A
- Localized, spot-like (macula adherens)
- Provide structural and mechanical strength
- Very present in skin
Structure:
-
Desmocolin & Desmoglein
- Interlock with adjacent cells
-
Plakoglobins & Desmoplakins
- form electron-dense plaque to attach desmocolin/desmoglein to intermediate filaments
Additional Image:
- Spines of stratum spinosum that retain contact as cell shrinks (desmosomes)
13
Q
Gap Junctions
A
- Allows cell communication
- Form channels to allow molecules to pass from one cell to another
- Can coordinate metabolic and electrical activity
Structure:
-
Connexins
- Transmembrane proteins that form hexameric channels (connexons)
- Appears “zipper-like” without plaques
14
Q
Hemidesmosomes
A
- Basal Domain
- Has electron-dense plaque to connect to basement membrane
- Integrins proteins
- Attach to intermediate filaments
- Abundant in skin, oral cavity, esophagus, etc.
15
Q
Focal Adhesions
A
- Found in epithelial cells undergoing repair/reorganization
- Link to actin filaments and extracellular matrix
16
Q
Microvilli
A
- Cytoplasmic projections that increase surface area for absorption
- Found on intestinal epithalial cells
-
Actin filament core
- These filament anchor into transverse actin filaments called the terminal web
- Glycocalyx is a coat of gylcolipids and glycoprotein covering (purple-pink border in PAS stain)
17
Q
Microvilli LM
A
- Brush border visible
- Will label well with PAS stain due to glycocalyx
18
Q
Microvilli EM
A
- Finger-like projections
- Core of wire actin filaments
- Covered with hazy glycocalyx
19
Q
Cilia
A
- Longer than microvilli and motile (move substances across epithelial surface)
- Found in respiratory tract and reproductive tract (oviduct)
-
Axoneme core (9+2 microtubule arrangement)
- Dynein (ATP-powered)motor protein slide microtubules past each other to produce cilia movement
- Basal Bodies are a modified centriole that is located directly beneath cilia
20
Q
Cilia LM
A
- Visible as hair-like projections
21
Q
Cilia EM
A
- Whole structure often not visible
- Axoneme cytoskeletal structure visible (9+2 arrangment)
23
Q
Stereocilia LM
A
- Individually discernable
- Similar in appearance to cilia
24
Q
Stereocilia EM
A
- Array of actin filaments make up projection
26
Q
A
Simple squamous epithelium
Functions
- Selective barrier (endothelium of blood vessels)
-
Lubrication of internal body cavities
- Serous lining of body cavities: Mesothelium
Locations:
- Walls of alveoli
- Visceral pleura covering of the lung
- Kidney (Bowman’s Capsule)
- Endothelium of blood vessels
27
Q
A
Simple cuboidal epithelium
Functions:
- Absorption, secretion, active transport of ions
Locations:
- Ducts of endocrine glands
- Renal tubules
- Ovary covering
- Thyroid follicles
28
Q
A
Simple columnar epithelium
Functions:
- Protection, lubrication, absorption, secretion
Apical surface usually covered in cilia or microvilli
Locations:
- GI tract, oviduct, renal collecting ducts
29
Q
A
Stratified squamous epithelium
Function:
- Protection
Keratinized:
- surface cells accumulate keratin protein and lose nuclei
- This prevents water loss
- Skin epidermis, hair, nails
Non-Keratinized:
- Surface cells retain nuclei (oral cavity, esophagus, vagina)
30
Q
A
Pseudostratified columnar epithelium
- Tall, irregular cells. Every cell contacts basement membrane
- Often ciliated
Functions:
- Protection, secretion and movement of substances
Locations:
- Respiratory tract: pseudostratified ciliated columnar epithelium (PCCE)
31
Q
A
Transitional Epithelium (Urothelium)
- Variability in cell shape and numbers of layers
- Superficial layer of larged, domed cells (umbrella cells)
- Has keratin intermediate filaments
Functions:
- Protection
- Distensibility
Location:
- Urinary Tract
35
Q
A
Goblet Cells
- Unicellular glands that secrete mucous
- Nucleus and organelles in stem
- Mucous in the “cup”
Locations:
- Intestinal and respiratory epithelium
39
Q
Serous Glands
A
- Produced thin, watery secretions (e.g. enzymes)
- Usually acinar shaped
- Typically stain intensely with H&E
- Secretory vesicles are eosinophilic and apical
- Nucleus and organelles are basal
40
Q
Mucous Glands
A
- Viscous, carbohydrate-rich secretion (mucins)
- Paler H&E stain (mucins don’t stain well)
- Usually tubular
- Appear round-tube
- Nuclei in basal portion of cell
Examples: goblet cells; submandibular glands
42
Q
Lipid Secreting Glands
A
- Secrete lipids
- In adrenal cortex, sebaceous glands
44
Q
Holocrine
A
- Secretory products accumulate in cytoplasm and are released via cell apoptosis
- Sebaceous Glands
45
Q
Apocrine Secretion
A
- Products accumulate in apical portion of cell & are released within membrane-enclosed vesicles (pinch off from apical plasma membrane)
- Mammary glands
