Epithelia and Glands Flashcards
2 main characteristics of epithelial cells
- closely apposed and adhere to one another via cell-cell adhesion junctions
- Have polarity
Describe the polarity of epithelial cells
- apical domain (free surface)
- lateral domain (surfaces that face neighboring epithelial cells)
- basal domain (attached to basal lamina
Location/catergories of epithelium
- covering the surface of the body (skin)
- Exocrine and endocrine glands
- Lines peritoneal, pleural, and pericardial cavities (mesothelium)
- likes blood and lymphatic vessels (endothelium)
functions of epithelium
Covering
Sensory
Myoepithelium
- protection (skin)
- secretion (glands)
- absorption (small/large intestine)
- gas exchange/Resperatory (lung alveoli)
- transport between blood and tissues (vascular endothelium)
Simple vs. Stratified epithelium
simple = one layer stratified = multiple layers
shape of epithelium
DEPENDS ON MOST APICAL SURFACE OF CELLS
squamous, cuboidal, columnar
Simple squamous
single layer and adhere closely to one another via edges
EX:
meothelium (line cavities) and endothelium (vessel)
Renal Tubules:? outer bowman capsule
Pulmonary alveoli
THINK: allow for diffusion
Simple Cuboidal
single row of square/low rectangular cells where the height and width of the cells are nearly the same
EX:
small ducts of exocrine glands;
Renal tubules: collecting ducts in kidney`?
Thyroid gland follicles
Simple Columnar
defined rectangular outlines where the cells are taller than they are wide
- nuclei are about the same level and end to be elongated
EX:
Small and large intestines
Stomach
Gallbladder and bile ducts
uterine mucosa- endometrium snd inner epithelium of uterine cervix
stratified squamous
- thick, many layers of cells with nuclei sort of aligned
- deep cells (near basal laminar) are more cuboidal, surface cells are squamous
- either keratinized or non-keratinized
Keratinized stratified squamous
-thickened plasma membrane and bundles of tonofilaments (keratin intermediate filaments) in cytoplasm.
-NO NUCLEUS in keratin portion
-on open (free surfaces).. exposed to world/abrasion
-provide thickness for increased protection
EX: epidermis of skin, palm of hand/feet
tonofilaments
type of keratin intermediate filament found in keratin stratified squamous cells
Non-keratinized stratified squamous
-found on inner/moist surfaces EX: esophagus oral cavity, pharynx, oesophagus nasal vestibule, vocal cords larynx anal canal (transitions into weakly K) vagina
stratified cuboidal
- deep layers = irregular polyhedral cells that do not reach free surface
- superficial (apical) cells = cuboidal
- EX: ducts of sweat glands
stratified columnar
- deep layers = irregular polyhedral cells that do not reach free surface
- superficial (apical) cells = columnar (taller than wide)
- EX: LARGEST ducts of exocrine glands
TRANSITIONAL ZONES: anorectal junction (into non k stratified ep) uterine cervix (into non k stratified ep)
pseudostratified columnar
- SIMPLE EPITHELIUM BU ALL OF THE CELLS DO NOT REACH THE FREE SURFACE
- nuclei NOT aligned (stratified)
- EX: goblet cell (ciliated) in respiratory system = respiratory epithelium
Transitional epithelium
- shape of superficial (apical) cells can change depending on relaxed (contracted) or distended (stretched)
- In relaxed (contracted): basal cells = cuboidal/columnar, apical cells = dome shaped
- in distended (stretched): cells look squamous because the bladder is filling
- EX ** urinary system: ureter, bladder
Apical domain location
free surface of epithelial cells; directed towards the lumen of an enclosed cavity of tube or the external environment (PART OF THE CELL THAT INTERACTS WITH THE ENVIRONMENT)
apical domain function
secretion, absorption, protection, transport of materials along the surface/into the epithelium, transduction of external stimuli via receptors
list the apical domain modifications
cilia, microvilli, sterocilia
lateral domain of epithelial cells: Location
- facing neighboring epithelial cells
- sometimes form interdigitations to increase surface area for cell-cell interactions
lateral domain of epithelial cell: function
adhesion of neighboring epithelial cells, cell-cell communication, creation of osmotic/ionic gradient
Basal domain of epithelial cell: location
- above the ECM
- associated with basal lamina and ECM adhesion junctions
Basal domain of epithelial cell: function
attach epithelium to the underlying CT (loose connective tissue)
Cilia function
move fluid and particles along the epithelial surface
cilia structure
- axoneme (9+ 2 microtubules, 2 microtubules in center)
- Basal body (MTOC: 9+ 3 microtubules) anchors cilium to apical region of the epithelial cell cytoplasm
how is the beating movement of cilia produced?
movement of doublet microtubules (in axoneme) in relation to each other via dynein
dynein
protein that allows microtubule doublets to move in relation to eachother
structure of axoneme vs. cilia basal body vs. centrosome
axoneme: 9 + 2 microtubules (with dyenin on them) with 2 microtubules in center
cilia basal body: 9 + 3 microtubules
centrosome: 9 + 3 microtubules
where are ciliated epithelia found?
trachea, bronchi, and oviducts
common disorders due to immotile (dysfunctional) cilia
- chronic respiratory problems
- Kartagener’s syndrome (absence of dynein causes male sterility due to immotile flagella)
- Young’s syndrome: malformation of radial spokes and dynein arms
Microvilli general/function/examples
cytoplasmic projections on the apical surface of epithelial cells
- NOT involved in movement of particles
- Involved in INCREASED ABSORPTION (by increasing the surface area of PM
- EX: intestinal absorptive cells (small intestine) = striated border, kidney tubule = brush border
Microvilli structure
- bundle of actin filaments attached at the membrane ti and extended down into the cytoplasmic terminal web
- core of actin filaments joined by actin-crosslining proteins (villlin and fimbrin)
- actin linked to membrane via myosin I and calmodulin
- terminal web
- glycocalyx (integral membrane glycoproteins)
terminal web of microvilli
contains actin, IM filaments, linking molecules; anchor into the junctional complex
glycocalyx of microvilli
- made of integral membrane glycoproteins that interact with the external environment
- aid in trapping or slowing external molecules close to the cell surface
- in intestines, it contains digestive enzymes
Steroecilia (what, what made of, where found)
- long, slender, immotile structure
- ACTIN core (similar to microvilli)
- found in epididymus and ductus deferns; sensory hair of inner ear
Stereocilia structure
- cytoplasm = actin bundles anchored to terminal web
- arise from apical protrusions at base
- thin stereocilia are sometimes linked via cytoplasmic bridges
- at finger-like region, actin are crosslinked by fimbrin and anchored to PM via ezrin
- in aprical protrusions & terminal web, actin crosslinked by alpha actinin
cilia vs. microvilli vs. stereocilia filament composition + mobile?
Cilia: microtubules; motile
Microvilli: actin; motile
Sterocilia: actin; immotile
Junctional Complex
- epthelial cell-cell adhesion junction
- aka “terminal bar” in LM
- 3 zones: zonula occludens, zonula adherens, macula adherens
Zonula Occludens function
-impermeability to apical/outersurface; permeability to lateral cells (FORM GRADIENTS FOR TRANSPORT of water across epithelium)
where can desmosomes be found
as part of junctional complex (macula adherens), or by themselves between two epithelial cells (as in keratinocytes of skin)
Gap Junctions function
-communicating junction
-not just in epithelium
-facilitate the movement of ions and small regulatory molecules between cells
CHEMICAL AND ELECTRICAL COUPLING BETWEEN ADJ. CELLS
gap junction structure
- 6 connexins = pore like connexon
- connexons from 2 cells are arranged to form a cylindrical channel between the cytoplasms of 2 cells
Pemphigus folliaceus
human blistering disease where autoantibodies against desmoglein I (transmembrane protein in the desomosome) causes a loss of skin cell adhesion
What results from connexin mutations?
- deafness
- charcot-marie-tooth disease (degeneration of peripheral nerves)
- congenital cataracts (opacity of the lens of the eye)
Basal Lamina location/composition
- specialized ECM
- located between the basal surface of epithelial and underlying CT
- 2 layers: lamina lucida and lamina densa
Lamina Lucida
layer of BL; ELECTRON LUCID
-contains: laminin, EC cell adhesion molecules, fibronectin and laminin receptors
Lamina Densa
layer of BL; ELECTRON DENSE
- contains fibronectin and laminin (proteins), type IV collagen, heparan sulfate proteoglycans, entactin (links laminin to type IV collagen)
- produces by epithelial cells
Function of Basal Lamina
- structural attachment (epithel to CT)
- Transport barrier (must cross BL to get from epithel to CT)
- Filtration (in kidney)
- Functional polarity (epithel adhere to BL)
- Regeneration (scaffold for tissue regen. post wound)
* *IN NERVE/MUSCLE SIMILAR LAYER; “EXTERNAL LAMINA”
Basement Membrane
Basal Lamina + lamina reticularis
lamina lucida + lamina densa + lamina reticularis
lamina reticularis
layer in basement membrane that contains type III collagen (reticular fibers) produces by underlying CT (fibroblasts)
Stains pink with Periodic Acid Schiff (PAS) base staining.. stains carbs
what does periodic acid Schiff stain
PAS STAIN
stains carbohydrates and carb-rich macromolecules pink
Hemidesmosomes location and function
location: basal cell layer of epithelium, prevalent in epithelia that need strong adhesion to CT
function: cell-ECM adhesion
How do hemidesmosomes anchor?
link keratin IM filaments in cell to the basal lamina (lamina lucida) via anchoring filaments (laminin 5 and collagen type IV)
Hemidesmosome associated cytoskeletal filament:
intermediate filaments (keratin) to intracellular attachment plaque
Hemidesmosomes proteins
bullous pemphigoid antigen I (BP230) + plectin in plaque linking keratin to integrin (transmembrane linker protein)
bullous pemphigoid
human blistering disease where autoantibodies against hemidesmosome components causes blisters between the basal lamina and basal surface of epithelial cells in skin, esophagus, and other tissues
focal adhesions
- structural links between actin cytoskeleton and proteins of basal lamina
- cytoplasmic face binds actin; extracellular face w/ integrins bind to basal lamina proteins
gland
a cell, group of cells, or organ that produces a secretion that is used by other cells or affects other cells
2 types: endocrine and exocrin
Endocrine glands
- prodcuts released into blood
- NO DUCTS
- local (does not enter blood) and systemic effects
- products = hormones
- in a tissue (unicellular) or multicellular
paracrine effect
local endocrine secretion that does not enter to the blood
Exocrine glands
- products released through surface of epithelium
- released into a lumen connected to a DUCT (multicellular); released directly onto surface (unicellular)
Goblet cell
- a unicellular exocrine gland that secretes its product directly onto the epithelium surface (in resp. epithelium)
- product = mucus to protect epithelial cell srufaces
muticellular exocrine glands
organized secretory cells associated with a duct
simple vs. compound gland
multicellular exocrine gland; dealing with the type of duct unit
simple: unbranched duct
compound: branched duct
Tubular vs. acinar vs. mixed gland
multicellular exocrine gland; dealing with the type of secretory unit
tubular: secretory cells arranged in a tube
acinar: cells arranged in a rounded shape (aka alveolar)
Mixed: both tubular and rounded
Mucus gland (type, product, stain)
EXOCRINE gland
product: thick protective lubricant (mucus) = mucin + water
Stain: pale in H&E
Serrous Glands (type, product, stain)
EXOCRINE gland
product: protein/enzyme rich watery fluid
stain: dark with H&E
Mixed serous/mucus glands
secrete both mucus and serous fluid; stain in some areas (serous) and dont in others (mucus)
methods of exocrine secretion
- merocrine secretion
- apocrine secretion
- holocrine secretion
merocrine secretion
- release of product AT APICAL SURFACE via EXOCYTOSIS
- most common method of secretion
ex: apocrine glands, pancreatic acinar cells
apocrine secretion
- free, unbroken, MEMBRANE BOUND VESICLES released (contain secretory product)
- small portion of the apical cytoplasm is released along with product
- NOT COMMON
ex: lactating mammary gland
Holocrine secretion
- ENTIRE cell dies and becomes part of the product
- NOT COMMON
ex: sebaceous glands of skin, meibomian glands of eyelid
cilia cytoskeletal comoponent
axoneme (9+2) arrangement of microtubules
microvilli cytoskeletal comoponent
core of actin filaments
sterocilia cytoskeletal comoponent
core of actin filaments
cilia cytoplasmic anchoring
basal body (9 triplet microtubules)
microvilli cytoplasmic anchoring
terminal web actin crosslinked with SPECTRIN
stereocilia cytoplasmic anchoring
terminal web actin crosslinked with ALPHA ACTININ
cilia membrane linking proteins
N/A
microvilli membrane linking proteins
myosin I and calmodulin (intestinal)
sterocilia membrane linking proteins
ezrin
microvilli: actin crosslinking proteins
villin and fimbrin (intestinal)
stereocilia actin cross linking proteins
fimbrin
cilia function
oscillation; move things along epithelial surface
microvilli
increase surface area for absorption or secretion
stereocilia
sensation or other function
zonula occludens associated cytoskeletal filaments
actin
zonula occludens transmembrane linker (TML) protein
occluden and claudin
zonula occludens protein linking TML to cytoskeletal filament
ZO-1, ZO-2, ZO-3
zonula occludens function
isolate lateral space from external space; concentrate solutes
zonula adherens associated cytoskeletal filaments
actin
zonula adherens transmembrane linker (TML) protein
cadherins (Calcium dependent)
zonula adherens protein linking TML to cytoskeletal filament
cathenins
zonula adherens function
cell-cell adhesion; anchor actin filaments
macula densa associated cytoskeletal filaments
intermediate filaments
macula densa transmembrane linker (TML) protein
desmocollins + desmogleins (a form of cadherins.. Ca2+ dependent)
macula densa protein linking TML to cytoskeletal filament
desmoplakin + plakoglobin (plaque)
macula densa function
cell-cell adhesion; spot welds
