Recap: Epithelium
- one of four basic tissues
- avascular/cellular
- specialized cells according to function
- occurrence:
sheets of cells (=lining)
solid aggregations of cells (=glandular)
Epithelial Classification
Layers
Cell Shape
Squamous
Columnar
Simple
Cuboidal
Pseudostratified
Squamous
Stratified
Cuboidal
Transitional
Stratified Epithelia
- consists of multiple layers
=> even if there are just 2 layers = stratified
- only basal layer of cells attached to the basement
membrane
- if cells appear stratified but contain cilia, they are
pseudostratified
=> True stratified epithelia do NOT have cilia
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Stratified Squamous
- bottom layer in contact with basement
membrane
- other layers adhere to one another
- referred to as squamous
=> many cell layers not flattened
- may vary from few to many layers
Non-keratinized: cornea, lips, oral cavity,
esophagus, vagina rectum
Keratinized: skin, lips
Keratin
-fibrous structural protein
-tough, insoluble
!Rivaled by chitin only
-consituent of structures growing from
skin
-soft epithelial keratin and hard hair
keratin
-nutrition of infectious fungi, i.e.
athlete’s foot
Stratified Cuboidal
-multiple layers of cuboidal cells
-found e.g. in sweat gland and male
urethra
-in most places two-layered
-only in ovary can they become large and
multilayered
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Transitional
- also called urothelium
- urinary tract only
- multiple cell layers, cuboidal in appearance
- cell can expand and contract
- expanded = cells squamous in appearance
- function:
accommodates volume fluctuation
protection against caustic urine
Apical Domain Modifications
Microvilli
- fingerlike projections on most epithelial cells
- highly varied in appearance
- form brush border on apical surface
- absorbtion, secretion, adhesion, transduction
Stereocilia -unusually long, immotile microvilli
-male reproductive system and ear
-resemble hairs of a paintbrush
Cilia
- mobile cytoplasmic structures
- female reproductive system, respiratory tract
- organized core of microtubules in 9+2 pattern
=> ectopic pregnancy
Lateral Domain Adhesions
Occluding
Junctions
- closely associated areas (vertebrates only)
- prevent movement between cells
= no passive/active transport
=> receptor mediated
- strands of transmembrane proteins
Anchoring
Junctions - cell adhesion molecules
- desmosomes
=> attach adhesion proteins to intracellular keratin
Communicating
Junctions
- gap junctions
- small molecules pass freely
- heart, neurons, eye
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Basal Domain Adhesions
- non-cellular
- lamina densa (30-70nm thick)
- underlying network of reticular tissue
- also contains macromolecule components
= basement membranes
Function:
1. anchoring epithelium
2. mechanical barrier against malignant cells
3. development of new blood vessels
4. glomerular filtration
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