Epithelium Flashcards
general features of epithelia
linked tightly together by intracellular junctions, found in the lining of all cavities and surfaces
major function of epithelia
barriers between two compartments
epithelium
free apical surface, and basal surface that rests on a non-living layer of ECM (basement membrane)
basement membrane
non living layer ECM, consists of true lamina (secreted by epi cells) and reticular lamina (secreted by conn. tissue cells)
classification of epithelia
simple, stratified, pseudostratified // squamous, cuboidal, columnar
simple epithelia
one layer of cells, all cells touch both free apical surface and basal surface touching basement membrane
stratified epithelia
more than one layer of cells, In a stratified epithelium, the apical or superficial layer of cells faces the free surface and is separated from the basal lamina by one or more layers of cells.
pseudostratified epithelia
all cells rest on the basal lamina, but only some have a free surface. arrangement of the nuclei is distinctive.
squamous features
wide, flat, nuclei bulging out of apical surface
cuboidal
cube-shaped. nucleus is round, and in the centre of the cell. cells that are wider than tall = low cuboidal
columnar
taller than wide. nucleus is elongated, and on the basal side
modifications
apical surface usually has modifications - microvilli, cilia, and stereocilia
parenchyma
secretory section of glandular tissue
types of tissues
epithelia, connective, nerve, muscle
places you find epithlia
sheets of cells lining cavities and open spaces.
functions of epithelium
barrier, protection, absorption, secretion, transport
how does epithelia protect?
abrasion resistance - layers of dead cells (skin), mucous secreting cells; line outside of digestive organs and protect as they all slosh and bump into each other
what does epi do to increase absorption + secretion?
fold a lot to increase SA
how much blood vessel content?
no blood vessels
types of apical specializations?
microvilli, cilia, stereocilia
microvili features
cylindrical projections; 0.5-1.0 microns, increase surface area for absorption, create a “brush border” pattern, seen in digestive tract and kidney, <50% size of nucleus
microvili structure
actin, hollow inside, cannot actively move, core joins actin cytoskeleton, cannot usually see individual microvili