Epithelium Flashcards
Simple Squamous Epithelium
Structure: Wider than tall |
Function: passage, transport (ex. blood in circulatory)
Location: lining of: blood vessel | lymph vessel | closed body cavities | some tubules | cornea
Types of Simple Squamous Epithelium & Location
Endothelium: line blood vessels & lymph vessels
Mesothelium: line closed body cavities, cover organs
Simple Cuboidal Epithelium
Structure: same length & width (judgement-based)
Function: ducts to carry secretory product
Location: line: ducts of glands (salivary) | kidney ducts
Simple Columnar Epithelium
Structure: taller than wide
plan or modified (+/- goblet cells/microvilli)
Function: protective | immune cells | secretory/absorptive
Location: line: gall bladder | GI tract | organs for
secretion/absorption
Pseudostratified Epithelia (Types & Structure)
Pseudostratified Columnar Epithelium
Transitional Epithelium
All cells contact basement membrane but not all reach free surface
Pseudostratified Columnar Epithelium
Structure: all cells attach to BM, not all reach surface | taller than wide | +/- modification (goblet cells, cilia, microvilli) | no line of nuclei at surface
Function: absorption
Location: line: respiratory tract | reproductive tract
Pseudostratified Columnar Epithelium w/ Goblet Cells (F)
Function: mucus secretion to prevent dehydration
Pseudostratified Columnar Epithelium w/ Cilia (F)
Function: trapping
Pseudostratified Columnar Epithelium w/ Stereocilia (S&F)
Structure: actin | finger-like projections
Function: fluid-absorption
Transitional Epithelium
Structure: increase size as layers closer to surface | “pillow-shaped” | no epithelial pegs
Function: stretching
Location: urinary tract
Apical Membrane Extensions (purpose & types)
Mediates absorption & secretion into lumen b/c epithelial cells have sealed apical ends
Types: Microvilli | Glycocalyx | Stereocilia | Cilia/Flagella
Microvilli
Structure: actin filaments for anchorage
Function: increase surface area for absorption
Location: epithelia of kidney & intestine
Brush Border
Microvilli + Glycocalyx
Seen as striated border
Function: absorption
Glycocalyx
“Cell coat” of glycoproteins | rich in carbohydrates
Protect free surface of epithelia
Stereocilia
Structure: “finger-like” projections | actin | very long
Function: fluid-absorption
Location: epithelium of epididymis | inner ear
Cilia / Flagella
Structure: uniform | axoneme (skeleton) from microtubules
inserted into basal body (centriole); anchored in cytoplasm
Single cilia = flagella
Function: bending, motility (by ATP w dynein motor protein)
Junctions (F & Types)
Function: strength | hold cells together
Types:
Impermeable Junction = Zonula Occludens (tight junction)
Adhering Junction = Zonula Adherens (terminal web/bar, desmosome)
Communicating Junction = Gap Junction (Nexus)
Zonula Occludens
Impermeable junction | “tight junction”
Structure: network-like | multiple belts of adhesion
Function: controls diffusion | strong seal of junction
Zonula Adherens
Adhering Junction | Terminal Bar & Terminal Web
Structure: filled w/ transmem proteins | actin (microfilaments) insert electron-dense plaque
Function: attach cytoplasm of cells together | strength/contraction
Terminal Web (S&F)
Structure: layering / network of actin across cell
Function: Strength & Increase Surface Area
Macula Adherens
Adhering Junction | Desmosome
Structure: VERY strong | disc shape | intermediate filament (cytokeratin) insert into plaques –> form hairpin loops
Complete desmosomes: between cells
Hemidesmosomes: to basal lamina
Function: adhesion of cells
Communicating Junction
Gap Junction (Nexus)
Structure: bridged by connexons (hexamer)
Function: intercellular communication | nutrition
Connexons
Protein in Gap Junction (Communicating Junction) that creates a pore & allows for Ca2+ transfer, membrane depolarization, and nutrients across cell
Basal Cell Membrane
NOT basement membrane
Structure: part of cell membrane below impermeable junction & contacts extracellular fluid compartment
Has Na/K pumps | hormone receptors | vesicles for transport across cells
Hemidesmosomes attach BCM to BM
Basement Membrane
Structure: basal lamina + reticular lamina
Function: attachment & orientation of epithelium | exchange/filtration through basal lamina (ie capillary)
Hemidesmosomes
Macula Adherens (Adhering Junction)
Attaches BCM to BM
Basal Lamina
Part of basement membrane
Secreted by Epithelium
Structure: electron-dense | collagen IV network | laminin glycoprotein | proteoglycan w/ heparan sulfate= (-) charge for attachment | rich in carbs
Stain: w/ PAS
Reticular Lamina
Part of basement membrane
Secreted by Connective Tissue
Structure: reticular fibers of collagen type III & VII (irregular fibers) + elastic elements (for stretching)
Stratified Squamous Epithelium (S & Types)
Structure: flat cells on surface
Types: Nonkeratinized or Keratinized
Nonkeratinized Stratified Squamous Epithelium
Structure: NO dry layer | visible nuclei | wet surfaces (no need for corneum layer) | “pegs”
Layers: Stratum Superficiale (top) | Spinosum (“spiny” desmosomes) | Basale (attach to BM)
Location: wet surfaces | carnivore esophagus | anterior cornea
Keratinized Stratified Squamous Epithelium
Structure: Cornified top layer | “pegs” for anchoring
Layers: Stratum corneum (nuclei invisible, dead cell layer, many filaments) | Lucidum (translucent, thin) | Granulosum (granules) | Spinosum (spiny/desmosomes) | Basale (bottom | hemidesmosomes)
Location: hairless areas | paw pads | nose | body openings
Keratin Types & Location
Soft: pliable | low sulfur | high lipid
Location: epidermis (skin)
Hard: non-pliable | high sulfur | low lipid
Location: claw | horn | fingernail
Keratinization Process
-Starts in stratum spinosum
-Keratin synthesis/accumulation (cytokeratin) until replaces active cytoplasm
-Lysosomal enzymes & hydrolysis of nonkeratinized cells (golgi, mito, nuclei)
Stratified Cuboidal / Stratified Cuboidal Epithelium
Structure: bistratified (2 cell layers) | surface row of nuclei | nuclei height indicates cuboidal v columnar
Function: carry secretory product
Location: large excretory ducts of glands | esophageal glands | distal urethra
Exocrine Glands
Empty secretion into duct system
Contact with body surface
Example: tear | sweat | mammary glands
Endocrine Glands
Empty secretion directly into blood (“ductless”)
No contact with body surface
Location: thyroid | adrenal | pituitary
Exocrine Gland Classifications
Morphological Characteristics
Nature of Secretory Product
Mode of Release of Secretory Product
Simple Glands
Exocrine
Single, unbranched duct
Types:
Simple Tubular
Branched Tubular
Coiled Tubular
Simple Acinar
Simple Tubular Glands
Single, straight secretory unit
Empties directly into lumen of organ
Branched Tubular Glands
Top gland opening, then branching
Coiled Tubular Glands
Coiled (bottom portion) and straight segment to surface
Location: skin, ear canal
Simple Acinar Gland
Enlarged secretory unit | spherical
Location: sebaceous glands (ie hair follicle)
Compound Glands
Extensive, branched duct system
Structures in compound glands:
Lobules
Interlobular ducts (excretory duct)
Intralobular ducts (secretory duct | intercalated duct)
Excretory Duct
Interlobular duct
Structure: Large | lined with simple or stratified epithelium
Function: transfer secretory unit –> action site
Secretory Duct
Type of Intralobular Duct
Structure: lined with simple columnar epithelium
Function: contribute to secretory product
Intercalated Duct
Type of Intralobular Duct
Structure: lined with simple cuboidal epith
Function: connect secretory unit w/ secretory duct
Gland Structures Classified by Nature of Secretory Product
Mucous secretory unit
Serous secretory unit
Mucoserous secretory unit
Acinus
Alveolus
Mucous Secretory Unit
Structure: nuclei “flattened” at base | columnar/cuboidal shape
Function: secrete mucin (light stain!)
Serous Secretory Unit
Structure: prominent | red stain | pyramidal shape
Function: watery secretion
Mucoserous Secretory Unit
Structure: mixed | mucous + serous cells | slightly darker stain | can split L/R, random, tubular/cap
Function: empty product (water/mucin) into intercellular canaliculi (canals between cells)
Acinus
Secretory unit w/ small lumen (low fill volume)
Location: pancreas
Alveolus
Secretory unit w/ large lumen (fill large volume)
Location: mammary gland
Merocrine Secretion
Aka eccrine
No visible change to cell integrity
Release via exocytosis
Location: salivary gland
Apocrine Secretion
Secretion w/ change to cell integrity
Cytoplasm “pinched off” into lumen of gland
Location: sweat gland | mammary gland
Holocrine Secretion
Entire cell lost as secretory product
Rod-shaped nuclei = cell necrosis (secretion)
Location: sebaceous gland –> sebum
Myoepithelial Cells
Modified epithelium w/ ability for contraction
Forces product out of secretory unit into the duct
