Epithelial Classification
Layers
Cell Shape
Squamous
Cuboidal
Simple
Columnar
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
Stratified Squamous
- bottom layer in contact with basement
membrane
- other layers adhere to one another
- referred to as squamous
=> many cell layers not flattened
=> named due to top, not bottom layers
- may vary from few to many layers
non-keratinizing: cornea, oral cavity,
esophagus, vagina, rectum and lips
keratinizing: skin, lips
1
Keratin
- fibrous structural protein
- tough, insoluble
=> rivaled by chitin only
- constituent 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
- ovary: large and multilayered
Transitional
- also called urothelium
- found only in the urinary tract
- multiple layers of epithelia cell, cuboidal in
appearance
- cell can expand and contract
=> depending on how full the bladder is
- when expanded become almost squamous in
appearance
- function:
accommodates volume fluctuation
protection against caustic urine
2
Epithelial Glands
Eccrine
sweat glands
Apocrine
sweat glands
Sebaceous
glands
Apical Domain Modifications
Microvilli
- fingerlike projections on most epithelial cells
- highly varied in appearance
- form brush border on apical surface
-absorbtion, secretion, adhesion, transduction
- bundled actin, with myosin and calmodulin
Stereocilia -unusually long, immotile microvilli
-limited to male reproductive system and ear
-resemble hairs of a paintbrush
- mysion replaced by erzin
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 (by diffusion
& active transport)
=> receptor mediated endocytosis
- network of sealing strands of transmembrane
proteins (claudins & occludins)
Anchoring - cell adhesion molecules (cadherins, integrins,
Junctions selectins, immunoglobulins
- homophilic & heterophilic binding
- desmosomes
=> attach adhesion proteins to intracellular keratin
Communicating - gap junctions
Junctions
- small intercellular molecules pass freely
- two connexons connect across intercellular
space
- heart, neurons, eye
3
Basal Domain Adhesions
- non-cellular
- contain:
1. electron dense lamina densa (30-70nm thick)
2. underlying network of reticular collagen fiber (0.1-2 µm
average)
3. macromolecule components
Function:
1. anchoring epithelium
2. mechanical barrier against malignant cells
3. essential for angiogenesis (development of new blood
vessels)
4. glomerular filtration
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