L5. Epithelium Flashcards
What are tissues?
Tissues are a set of morphologically similar cells that perform a function or a set of functions
What are the characteristics of epithelial tissues?
- Avascular ( no blood vessels)
- A group of continuous group of cells
- Are defined basally and apically. With basal end attached to the basement membrane. Apical end is the lumen formation
- There is no ECM between the cells
- Cells are attached to the basement membrane (ECM)
What are the 4 functions of the epithelial tissues?
1.protect underlying tissues
2.involved in the secretion of substances
(paracrine, endocrine, exocrine)
3.involved in the transport of substances
4.absorb substances ( usually have specialized structures)
What are the 2 types of transport (cellular)
- transcellular transport: involves the use of channels such that substances flow through these channels into the cell
- paracellular: substances flow between the cells at junctions without the tight junctions (adhesion is not tight)
What are the 3 forms of secretion
- paracrine: substances secreted basally into the BM of the ECM
- endocrine: substances are secreted basally into the BM of the ECM can eventually enter the bloodstream
- exocrine: secreted apically into the lumen into the external environment
How are lumens form?
Through the constriction of the apical zonular belt.
induces tubular morphogenesis
shape change
What causes the shape change during tubular formation
actin-myosin facilitates the contraction of the apical zonular belt.
What are the specialized apical structures?
- microvilli
2. cilia
Describe the microvilli
- can be seen as a brush border on the LM.
- can be resolved with the EM
- increases the SA makes absorption more efficient
- bundles of actin filament
- non-motile
- 1 um long 25nm wide
What is the dimensions of the microvilli
1um long 25nm wide
Describe the cilia
- facilitates in cell movement; motile
- 10um long, 250nm wide
- core of microtubules arranged in radial spokes
- individual structure seen on both LM and EM
What are the categories of cell layers?
- simple: only 1 layer all cells attached to BM
- stratified: multilayer ( see many nuclei down the vertical)
- pseudostratified: looks stratified ( many nuclei) irregularly shaped cells but all cells are attached to BM
What are the categories of cell shape?
- squamous: flattened
- cuboidal: looks like a cube
- columnar: looks wider by the sides
What are the different cell structures?
- simple squamous epithelium
- simple cubodial
- simple columnar
- stratified (keratinized) squamous
- stratified (not keratinized) squamous
- pseudostratified
- transitional
Functions of simple squamous epithelium
- lining epithelium
- lubrication
- located at sites for fluid and gas exchange
What structures have a simple squamous epithelium
blood and lymphatic vessels
loop of Henle
lining of internal body
thoracic cavity
Functions of simple cubodial epithelium
absorption
secretion
protection
What structures have a simple cubodial epithelium
tubules of kidney
ducts of glands
Functions/Features of simple columnar epithelium
absorption
secretion
transportation
- have an apical brush border
What structures have a simple columnar epithelium
found in gastrourinary tract and the digestive system
Functions/Features of stratified squamous (keratinized) epithelium
- protective
- waterproof
- has a layer of dead cells (enucleated)
- filled with keratin intermediate filaments
- has hemidesosomes
Functions/Features of stratified squamous (un-keratinized) epithelium
- protective
- many layers
- no layers of dead cells
- only basal layer attaches to the BM
What structures have a stratified squamous (keratinized) epithelium
outer layer of the skin
What structures have a stratified squamous (un-keratinized) epithelium
found in wet areas of the external/ internal transition of the GI, respiratory and geniuritonary tracts
- mouth
- larynx
- vagina
- anal cavity
- esophagus
- urethra
Functions/Features of pseudostratified
absorption secretion lubrication protective cells are of different height all cells attached to the BM often ciliated
What structures have pseudostratified epithelium
trachea primary bronchi nasal cavity epididymis vas deferens
What structures have transitional epithelium
-bladder
Functions/Features of transitional epithelium
stratified and distensible
when relaxed: cubodial
when stretched: squamous
(Draw for me tubular morphogenesis)
L5 pg 4a.
What adhesion protein is used in tubular morphogenesis?
zonular adherins
what cytoskeleton is involved in tubular morphogenesis
actin filament
