IAS20 Flashcards
function of epithelial tissues
PAESS
protection (work w/ connective tissue to act as phy barrier, stratified protect against injuries, abrasion, infection)
absorption & excretion (simple, facilitate efficient material transportation)
secretion (exocrine & endocrine)
sensation (specialized sensory receptors, convey signals to nervous system e.g. retina & olfactory)
6 characteristics of epithelial tissue
exhibit functional & morpho. polarity (prominent diff. in diff. side of cells)
contains cytokeratin (inter. filament) for providing strength to resist stretching
cells close together w/ little or no IC matrix, indi. cells joined by junctional complex
sit on basement membrane
avascular -> continuous layer, obtain nutrients & remove waste from connective tissue blood vessels
epithelium connection w/ connective tissue, basement membrane
epithelial supported by connective underlying, separated by basement membrane (acellular)
stained by periodic acid-schiff, blue
basal lamina: secreted by epithelium, type IV collagen
reticular lamina: secreted by fibroblasts in connective tissue, type III collagen
basement membrane function
attachment to connective tissue
act as scaffold to guide cell migration in tissue repair
classification of epithelia
shape of apical cell: squamous (flattened), cuboidal (equal dimensions, round nucleus), columnar (tall)
no. of layers: simple / pseudostratified (1), stratified (>1), transitional (varies)
general functions of epithelial types in cell layer & shape
simple: diffusion, secretion, absorption (filtration)
stratified: protection
squamous: diffusion (filtration)
cuboidal: secretion & absorption
columnar: highly active secretion & absorption
simple squamous epithelium
very thin, flattened
facilitate exch. of materials, absorption & secretions (maximise rate of diffusion)
e.g. tissues or cells using diffusion for molec. movement, pulmonary alveoli, lining heart, blood & lymph vessels; appendix, peritoneal & pleural cavity
simple cuboidal epithelium
contain more cytoplasm, for secretion, excretion & absorption
participate in active transport e.g. gland duct, bile duct, kidney tubule; thyroid
simple columnar epithelium
elongated nuclei located near base of cell
fluid transport, secretion & absorption (larger cell -> higher level of secretion & absorption than cuboidal)
e.g. intestinal lining, gallbladder
simple ciliated columnar epithelium
contain motile cilia e.g. fallopian tube
stratified squamous epithelium, non-keratinised
apical layers are living cells w/ nuclei
basal membrane generally cuboidal
intermediate cells usually polyhedral shape
for protection against desication & abrasion
e.g. uterus surface; esophagus
stratified squamous epithelium (keratinised)
cell on surface subject to mech. stress when exposed to high abrasion lvl
superficial layers contain rich amts of keratin but dead
surface protection & prevent desiccation / mech. stress / abrasion
e.g. skin
stratified cuboidal epithelium (note: no structure)
for protection, secretion & limited absorption
e.g. lining of larger excretory duct of exocrine glands (salivary, sweat)
stratified columnar epithelium
basal layer cells short & irregular shaped
for protection & secretion
e.g. larynx, larger ducts of exocrine glands (mammary gland)
transitional epithelium
shape of epithelium change under diff. circumstances, only found in urinary tract (ureter, urinary bladder)
protection & accomodate high degree of stretching
(superficial cells usually binuclear)
bladder relaxed state: apical larger than basal, cuboidal, bulge into cavity; sig. folding of cells -> more dark purple color
stretched: apical appear squamous
(upper epithelial surface fortified by plaque)
pseudostratified ciliated columnar epithelium
resp. system airway, resp. epithelium
cilia on apical surface, goblet cells present
morphological polarity of epithelial cells & examples
distinct specializations found on diff. surfaces of epithelial cells
apical: microvilli, cilia
lateral: junctional complex (ZO, ZA, desmosome), gap junction
basement: infolding, hemidesmosome
microvilli mechanism
immotile, protrude towards cavity / lumen, for absorption e.g. GI
myosin & tropomyosin in terminal web contract -> spreading out of actin core -> microvilli spread -> inter-microvilli space increase
cilia structure
motile, facilitate fluid movement e.g. respiratory & oviduct
has organised microtubule core:
9 doublet axoneme + 2 central microtubule arrangement, each doublet has dyenin branching arm to connect to adj. doublet, interaction allows beating action
joins to basal bodies in 9 triples
zonula occludens
wrap all the way around apical portion of cells
proteins brings membrane close to adj. cell -> tight seal -> restrict movement of substances passing btn cells
zonula adherens
wrap all the way around apical portion of cells
protein layer inside membrane attaches proteins & microfilaments
transmembrane glycoprotein: e-cadherin, interact w/ other cadherin protruded out of adj. cell to join cells; other side interact w/ terminal web
provides physical strength for cell-cell interactions
desmosome
circular plaques of neighbouring cells joined together by linker proteins which interdigitate in EC space
intermediate filaments insert into each plaque, bundles across cytoplasm & anchor at desmosome at other side of cell
provides mechanical strength for cell-cell interaction, hold adj. cells together
joins all intermediate filaments of whole epithelium into one continuous network -> resist stress as pulling force evenly distributed through the layer
gap junction
connexin proteins assemble into pores, join w/ pores of neighbouring cells
for communication between cells & transport of materials
basal infolding
infoldings extend close to nucleus -> inc. surface area of membrane to support active transport btn epithelium & connective tissues along w/ mito present
e.g. cells involving active absorption & secretion, kidney tubules, striated ducts in salivary glands
glandular tissue development
epithelial cells proliferate & grow into connective tissues OR
invaginate into connective tissues, separation by basement membrane
endocrine vs exocrine gland formation
endocrine: epithelial cells separate from original epithelium & form cluster of cells, no lumen, secretions released into connective tissues -> blood
exocrine: connected to epithelium w/ lumen at center, secretory portion (simple cuboidal) secrete products into lumen -> flow to surface through a duct (inactive epithelium)
classification by structure of exocrine glands: no. of ducts, no. of secretory units, morphology of glands
simple (1 duct) vs compound (many ducts)
tubular (1 secretory unit) vs branched (few secretory units)
simple coiled: spiral / convoluted secretory portion
tubular: uniform tubular lumen
acinar: large bulbous spherical collection of secretory & excretory cells, small lumen
alveolar: uniform size cells in large sac-like lumen
goblet cell & staining
single cell gland
apical portion contains many secretory vessels released by exocytosis into tract, nucleus at basal side
mucus does not stain well in H&E -> paler color
forms parts of protective mucus gel layer in tracheal & intestinal epithelia
classification by nature of secretory gland
mucous: flattened nuclei, secretes thick & slimy mucin; pale stain
serous: round nuclei, secretes water proteins creating eosinophilic cytoplasm in apical side; basophilic staining in basal aspect e.g. pancreas
mixed / seromucous: both e.g. salivary
salivary demilune
serous cells arranged as a cap on mucous cells
both cell types associated w/ e.o., e.g. salivary gland
mode of exocrine secretion
merocrine: exocytosis, no cytoplasm loss, e.g. sweat & salivary gland
apocrine: discharge of free, broken vesicles containing secretory product, e.g. mammary & lipid secretory
holocrine: cell ruptures & release secretory products e.g. sebaceous gland
mesothelium & endothelium
mesothelium: epithelium lining wall of serous cavities of body
endothelium: epithelial lining of blood & lymph vessels
