Epithelia Flashcards
Outline the functions of epithelia
Secretory, absorption, mechanical (protection)
What are the different types of shaped cells of epithelia?
Squamous (flat)
Cuboidal (square-like)
Columnar
What are the different types of stratification of epithelia?
Simple epithelium (simple, single layer)
Stratified epithelium (several layers)
Pseudostratified (appeance of layers, appear stratified but all reach BM)
Transitional (several layers, change shape)
What does basement membrane do for epithelia?
Anchor epithelium to connective tissue
What is BM in contact with?
Basolateral membrane
What synthesises BM (basal lamina)?
Epithelial cell
What does basement membrane contain?
GAGs and collagen proteins (laminins)
What are the functions of basement membrane (4)?
1) epithelial anchorage (structural integrity to epithelial layer - anchored by hemidesmosomes)
2) gives polarity to epithelial cells
3) regulation of cell growth, org and diff through cell surface receptor and ECM
4) Diffusion barrier
What anchors the BM to cells?
Hemidesmosomes (integrins in hemidesmosome, to laminins in BM )
What can and what can’t penetrate basement membrane, what’s the consequence?
Nerves can
Blood vessels can’t -nutrients reach epithelial cells by diffusion
What are 2 specialisations of epithelia?
Cilia and microvilli
Where are simple squamous epithelium found?
Bronchioles
Loop of Henle
Inside blood vessels
Serous membranes
Describe appearance of simple squamous epithelium, why?
Single layers of flat cells, nuclei appear as bumps as cells are flat
What are functions of simple squamous?
Diffusion, secretion, absorption and filtration
Where is simple columnar epithelium found?
Bronchioles
Intestine
Uterine tubes
Glands
Describe functions of simple columnar epithelium?
Bronchioles: move particles out of bronchioles
Uterine tube: move oocyte by ciliated cell
Intestine: absorption.
Describe structure of simple columnar cells?
May have cilia or microvilli
Where are simple cuboidal epithelium found?
Kidney tubules, terminal bronchioles, thyroid follicles
Describe structure of simple cuboidal epithelium?
Microvilli and cilia
What is the function of simple cuboidal epithelium?
Active transport, secretion, absorption
Describe where stratified cuboidal epithelium is found?
Salivary and sweat gland ducts
Describe function of stratified cuboidal epithelium?
Secretion, absorption and protection against infection (robust lining)
Describe where pseudostratified columnar epithelium is found?
Lining of nasal cavity, auditory tunes, bronchi etc
Describe structure of pseudostratified columnar cells?
Single layer of cells, some reach cell surface, nuclei appear at different levels
Ciliated and associated with goblet cells
Describe function of pseudostratified columnar epithelium?
Make mucus which traps particles then move mucus out
How is stratified squamous keratinised epithelium formed?
Epidermal cells differentiate and move up through epidermis becoming filled with keratin (and losing organelle)
Describe the function of stratified squamous keratinised epithelium?
Dead, keratinised outer layer prevents water loss
Where is stratified squamous keratinised epithelia found?
Skin
Where is stratified squamous epithelia found?
Mouth, throat, vagina
Where is transitional epithelium found?
Lining urinary tract (i.e . bladder, ureter, urethra)
How does transitional epithelium change?
Organ full: stratified squamous
Organ empty: stratified cuboidal cells
What is function of transitional epithelium?
Accomadate fluctuations in volume of fluid in organ and protect against urine
What are the roles of cell junctions?
Bind cells together & Maintain arrangement of epithelial cells into layers
What are functions of tight/occluding junctions?
Contribute to barrier function of epithelia
Number of TJ determine if epithelia is leaky or tight
Prevent lateral migration of floating membrane proteins
Maintain polarity (separate apical and basolateral membrane)
Seal intercellular space from luminal enivronment
What do anchoring junctions allow?
Provide epithelia with ability to resist shearing and tensile strength
What do anchoring junctions consist of in adherens junction?
Cytoskeleton (actin, microfilaments)
Cytoplasmic link protein (catenins)
Cell cell adhesion molecule (cadherins)
What do anchoring junctions consist of in desmosome junction?
Cytoskeletal (intermediate filaments)
Cell cell adhesion (Desmogleins)
Cytoplasmic link
(Desmoplakins)
What happens in pemphigus?
Antibodies to desmosome cadherins (desmogleins) -blistering of skin + mucous membranes
What are gap junctions regulated by?
Ca2+ and pH
Describe role of basolateral folds?
Fluid or ion transport functions in cells
How are apical and basolateral membranes distinct in 3 ways?
Morphological (e.g. villi)
Biochemical (e.g. protein distribution)
Functional (ion selectivity)
Describe difference between exocrine and endocrine glands?
Exocrine: retain contact with surface through duct, secrete onto external epithelial surface
Endocrine glands: secrete product into extracellular space and taken up by blood (don’t have duct)
What is glandular tissue?
Type of epithelium that forms glands from infolding of epithelium.
What can epithelia arise from (development)?
All three germ layers
What type of epithelia develops from each germ layer?
Ectodermal epithelia is stratified or pseudostratified. (glands of the skin, oral and nasal mucosa, cornea).
Endodermal epithelia is simple (lining of the small intestine, liver, pancreas, gall bladder).
Mesodermal epithelia is simple (kidney, pericardium, reproductive systems)
How are cell junctions visualised?
EM images
What do adherens junctions link?
Actin microfilaments
What do desmosomes connect?
Cytoskeletal intermediate filaments between epithelial cells
What is a junctional complex?
When several types of epithelial junctions are found in close proximity to each other
Why are adherens Ca2+ dependent?
Cadherins
