epithelial cells Flashcards
epithelial tissue
lines all tubes of the body and faces the open spaces (ie skin, GI tract). Functions in protection, active transport, biochemical mod, detox, communication between tissues, substance transport, respond to stimuli. Lay on top of connective tissue (including blood vessels) by their basal surface. Not vascularized, muscle and neurons also lie on connective tissue
classification of epithelia
simple (single layer), stratified (multi layer, outer layer do not touch basal lamina), pseudostratified (some cells don?t reach free surface, but all touch basal lamina), squamous (flat), cuboidal (cube-like), columnar (taller than width), transitional (in bladder, stratified but when stretched go to cuboidal and squamous
polarity
based on membrane and intracellular contents. Cytoskeleton plays an important role, as do pumps, secretory pathways, and membrane composition. Function includes unidirectional secretion or absorption, trans-epithelial transport of ions, endocytosis, exocytosis, transcytosis, localization and orientation of intercellular signaling.
cell junctions
tight junctions, adherins, gap junctions
tight junctions
link adjacent epithelial cells, forms a seal that separates apical and basolateral components, made of occludins and claudins, limit movement between cells, forces transport to go through epithelia, important in polarity
Adherins
made of cadherins, important for structual integrity, control signaling, Desmosomes are a type of e-cadherin that interacts with intermediate filaments (in skin)
Gap junctions
in cardiac muscle, form channels, allows passage via diffusion of small molecules between cells
cell surface mods on epithelial cells
microvilli, cilia, basolateral surface mods
microvilli
small protrusions loaded with actin, important for absorbtion rate by increasing surface area of cell
cilia
long wavy arms of microtubules, used for moving substances along epithelial sheet. Also sensory cilia that are not motile (in vestibular bar cells of ear.
basolateral surface mods
infolds and outfolds, lack structual organization of microvilli and cilia, increase surface area, seen in cells that transport heavily across basolateral surface
basal laminae
made of collagen, laminin, multidomain proteins; porous to small molecules, form attachment deep to epithelial cells and superficial to tissues, specific to attached tissue, very diverse
functions of basal laminae
connects various tissues, serve as barrier to cell movement, some promote filtration (ie kidneys), information-containing scaffold that dictates epithelial cell attachment and dynamics of transport
Hemidesmosome
core protein is integrin, interacts with intermediate filaments
focal adhesions
like adherin juntions, organize signalling complexes controlling polarity, gene expression, transport, etc within epithelial cells
exocrine glads
secrete materials onto apical side, generally multicellular, have two main components; 1) secretory units, clumps of secretory epithelial cells, produce and release bulk of secretions. 2) Ducts - tubular structures emanate from secretory units, passageways to conduct secretions to destinations, epithelia can modify secretions by secretory and ion transport. secrete unidirectionally from apical surface (except holocrine), secrete mucus and serous.
endocrine glands
no ducts, secrete into clood stream, produce specific hormones, act over long distances, organized as clumps or chords of cells, embedded/surrounded by connective tissue containing capillary network. Each clump surrounded by basal lamina, hormone molecules cross basal surface and basal lamina to reach blood stream, most endocrine cells secrete from the basolateral membrane
epithelial to mesenchymal transition
epithelia derived from all 3 primary germ laters. Early development, epithelia form, then disassemble, and reform in new patterns until proper morphology achieved, often disassemble and move into mesenchymal (connective) tissue, from here can migrate to other locations, or transfrom into non-epithelial cell lines. some embryonic epithelia serve as signaling centers thar organize patterns of formation
epithelial-derived cancers
Stem cells common target of disease (especially caner). Epithelial cancer is most common type (carcinomas). Exocrine carcinomas = adenocarcinomas, many embryogenic pathways used in caner (TGF beta, wnt signalling, sonic hedgehog, tyrosine kinases, notch). developmental pathways have different outcomes in different cell types, important clinically (ie WNT signaling in colon cancer, FAP specifically). APC mutated = beta catenin increases proliferation and de-differentiation
histological examination
section material from biopsy, put on slide, look at under microscope, fix tissue with chemical, then slice thinly.
general stains
bind acidic or basic compounds, see what is stained and not what isnt.
looking at slide
nucleus is usually dark, mucus fails to bind dye and appears white (unless dye binds carbs), if something is not fixed it can leach out and won’t be scene, main thing is find nucleus and compare from there
immunohistology
specific staining; immunohistochemistry and immunofluoresence
