Flashcards in Epithelium Deck (57):
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
free apical surface, and basal surface that rests on a non-living layer of ECM (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
one layer of cells, all cells touch both free apical surface and basal surface touching basement membrane
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.
all cells rest on the basal lamina, but only some have a free surface. arrangement of the nuclei is distinctive.
wide, flat, nuclei bulging out of apical surface
cube-shaped. nucleus is round, and in the centre of the cell. cells that are wider than tall = low cuboidal
taller than wide. nucleus is elongated, and on the basal side
apical surface usually has modifications - microvilli, cilia, and stereocilia
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
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
actin, hollow inside, cannot actively move, core joins actin cytoskeleton, cannot usually see individual microvili
modified microvilli, very long (75% cell), sparse and ragged looking, found in inner ear and male reproductive system
10x bigger microvilli, pinched appearance (beer bottle), sweeping motion moves material, found in respiratory and female reproductive (egg and uterus), has dark line beneath it (basal body)
microtubule skeleton (axenome), 9+2 arrangement of microtububles, anchor in cell = basal body = most important feature is dark line at the apical surface
epithelia are tightly packed. what holds them together?
cell junctions: tight junctions, adherens junctions, gap junction, and desmosomes IN THAT ORDER.
tight junction features
membranes are closely opposed, most apical of all the junctions, prevent movements between cells, chicken-wire/fishnet feature, occluding junction (no liquid can pass through)
adherens junction features
apical lateral cell junctions (just below tight junction), encircle cell completely, long parallel densities (space), NOT occluding aka liquid will get past them, consist primarily of cadherins
strong and lateral adhesion, static and structural, PROMINENT KERATIN FILAMENT WEB, parallel densities, usually straight, same cadherin famile as adherence junction, not concractile
gap junction features
tightly opposed membranes, generally below adherens junctions, collection of pores (connexons), regulates cell to cell communication through free movement of small molecules between cells
terminal bars features
all cell adhesion sites, artifact of fixation = vertical line with tiny little bulges
types of basal specialization
basement membrane, cell substrate adhesion
role of basement membrane
separates epithelium from connective tissue
basement membrane layers
basal lamina of epithelial origin (laminins), reticular lamina of connective tissue origin (often see collagen fibrils)
where find simple squamous? what surface modifications would you find?
lining all cavities, and all blood vessels, found where exchange occurs; no surface modifications
what is mesothelium
lines all organs; simple squamous
what is endothelium
lines all blood vessels; simple squamous
where find simple cuboidal? what are its functions? what surface modifications would you find?
lining tubes and glands; secretory and absorpative; mv/c/sc
where find simple columnar? what surface modifications would you find?
lines tubes (kidney, gallblader); apical modifications (mc/c/sc)
where would you find ciliated simple columnar cells?
oviduct only; no goblet cells present
where would you find simple columnar cells with microvili?
digestive tract - goblet cells are present here
where would you find pseudostratified columnar cells? what surface modifications would you see?
respiratory tract - will be ciliated; male reproductive tract - will be stereociliated
what layer should you look to in identifying which epithelium it is?
where would you find stratified squamous epithelium?
moist areas: nose, mouth, reproductive tract; where skin meets interior
what distinct feature does keratonized stratified squamous epithelium have?
where would you find transitional epithelium? why?
bladder - transition is very stretchy
what features does transitional epithelium have?
pillow-like apical cells; these are flat when stretched (full) bladder
what are the different glands? contrast them
exocrine and endocrine; exocrine secretes to free surface + is connected to surface + can form ducts; endocrine secretes to circulatory system + is not connected to surface + cannot form ducts + always round
what are the different types of exocrine glands? define them.
merocrine/eccrine (secretes directly), apocrine (vesicle), and holocrine (whole cell)
what is a goblet cell? what does it do?
unicellular exocrine gland; secretes mucous in the digestive and respiratory system
what is a duct?
multicellular exocrine gland; it's a specialised secretory unit
which types of glands do you find in pancreas?
both exocrine and endocrine; the exocrine are secreting digestive enzymes and are arranged into ducts, while the endocrine are secreting insulin and arranged into cords
why is epithelia so prone to cancer?
glandular cancer, excessive glandular tissue
common and metastatic, treated by excision
are moles carcinoma?
no, they are a proliferation of melanocytes, and do increase susceptibility to cancer