Rachael Curry Flashcards
epithelia =
cells that cover / line all body surfaces, tubes, and cavities
also form INTERFACES between different physiological fluid compartments
eg (1)- skin between body tissues and environment
eg(2)- vessel wall between blood and tissues
examples of abnormal epithelial function =
1) cystic fibrosis - defective epithelial Cl- ion transport
2) cholera - over-active Cl- ion transport in gut (Cl- leaves –> Na+ leaves –> water follows –> diarrhoea and dehydration)
3) breast cancer - over-proliferation of epithelial cells (NOTE- cancers derived from ep. = CARCINOMAS)
structural classifications of epithelia
columnar
cuboidal
squamous
columnar =
tall cells
big barrier to transport (large surface area to diffuse through)
cuboidal =
boxy cells
fair barrier to transport
squamous =
flattened cells
little barrier to transport
simple =
1 layer of cells
all cells in contact with lumen and basement membrane
found in sites of body where diffusion / absorption / secretion occur (gut / lungs / blood vessels / etc.)
stratified =
multiple layers of cells
cells in contact with lumen = apical
cells in contact with BM = basal
found in sites of body that require protection (mouth / skin / stomach / etc.)
basal vs. apical
basal is inferior to apical
basal = closer to basement membrane
apical = closer to lumen
simple squamous
single layer of flattened cells
gas exchange/ easy transport
eg- in blood vessel walls
functions - exchange
1 cell layer
squamous cells
pores between cells
eg- in lungs and blood vessels
functions - transportation
1 cell layer
cuboidal/columnar cells
tight junctions limit movement between cells
eg- in intestines/kidney
functions - ciliated
1 cell layer
cuboidal/columnar cells
cilia move fluid across apical surface
eg- in trachea/reproductive system
functions - protective
many cell layers
squamous on apical surface / polygonal on basal
tightly connected by DESMOSOMES
eg- in skin/mouth
functions - secretory
1 or more cell layers
columnar/polygonal cells
contain extensive (R)ER
eg- in endocrine / exocrine tissues
simple squamous
single layer of flattened cells
gas exchange / line body cavities
eg- in blood vessel walls (endothelium) / serous membranes (mesothelium)
simple columnar
single layer of cells
increase surface area for absorption
eg- in gastrointestinal tract
pseudo-stratified ciliated columnar
appearance of stratified BUT all cells in contact with BM and lumen
modified with cilia to facilitate function
eg- in respiratory tract
stratified squamous
many layers of cells
rapidly-dividing basal cells
protect underlying tissues from abrasion
eg- lining of oesophagus
keratinised stratified squamous
many layers of cells
resists water loss
subject to abrasion
eg- skin
types of trans-cellular movement
absorption
secretion
absorption
lumen —> apical compartment –diffusion etc.–> basal compartment = absorption
secretion
basal compartment –active transport–> apical compartment —> lumen —> blood/gland/etc. = secretion
paracellular movement
molecules move through junctions rather than the cell itself
relies upon diffusion OR active transport
gap junctions
function = communication cell-cell junction membrane proteins = CONNEXIN
types of cell junctions
gap
tight
adhering
(hemi)desmosomes
adhering junctions
function = anchoring cell-cell junction membrane protein = CADHERIN
desmosomes and hemidesmosomes
Desmosomes
function = anchoring
cell-cell junction
uses CADHERIN and INTERMEDIATE FILAMENTS
Hemidesmosomes function = anchoring cell-matrix junction membrane protein = INTEGRIN or KERATIN ECM protein = LAMININ
ROLE of tight junctions
BARRIERS
separate compartments
protective (sealing strands increase resistance against movement)
eg- urinary bladder
FENCES
maintain asymmetric distribution of lipids and proteins between apical / basal membranes
creates compartments w/different chemical compositions - localises receptors
eg- gastrointestinal tract
stratified cuboidal
multiple layers of cells
eg- in reproductive system (RARE)
Functional difference between epithelial and non-epithelial cells
non-ep = no way to orientate cells (no up/down)
whereas
ep = maintain a polarity (due to junctions) that orientates the cell layer
