Practical 2 - Epithelia Flashcards
What is the definition of an epithelium?
A cohesive sheet of cells with one or more layers, resting on a basement membrane.
What is the purpose of epithelia?
Form barriers for:
- protection
- absorption
- secretion
Simple vs stratified epithelia?
Simple - single layer of cells resting on a basement membrane.
Stratified - two or more layers of cells on a basement membrane.
What type is gall bladder epithelium?
Simple columnar epithelium
What type is oesophageal epithelium?
Stratified squamous non-keratinising epithelium.
Where is simple squamous epithelium found?
- blood vessel endothelium
- mesothelium (outside of lungs)
- peritoneum (outside of abdominal organs)
Where is simple cuboidal epithelium found?
Lines kidney tubules and small ducts.
Where is simple columnar epithelium found?
Lines stomach, intestines and uterus.
True or false: simple columnar epithelium can have cilia/microvilli?
True
What is the function of goblet cells in the small intestine?
Secrete mucin onto surface of epithelium as a lubricant.
How do cilia work? Where are they found?
Contain contractile proteins which enable them to beat rhythmically.
Respiratory tract & reproductive tract.
What are some features of stratified epithelium?
- protective
- many layers
- continually worn down and replaced by cells from below
Where is stratified epithelium found?
Sites subject to abrasive forces: skin, mouth, oesophagus, vagina, cervix.
How are cells replaced in stratified epithelium?
Immature cells rest against basement membrane. Cells are pushed up to the surface as they mature by new cells forming beneath them.
What is the function of keratin?
Keratin waterproofs the epithelium.
How is stratified squamous epithelium keratinised?
As cells mature they accumulate keratin within their cytoplasm. Eventually they die from this accumulation which leaves flat plates of keratin at the surface of the epithelium.
Example of stratified squamous keratinising epithelium?
Skin
What is pseudo-stratified epithelium? Example.
Single layer of cells, all in contact with the basement membrane but have varying heights. This creates the appearance of multiple cell layers.
Respiratory epithelium.
What is urothelium? Where is it found?
Specialised stratified (& pseudostratified) epithelium.
- surface layer of umbrella cells not in contact with basement membrane.
- several layers beneath the surface are in contact with the basement membrane but it’s uncertain exactly how many, could be a single pseudo-stratified layer.
- lines collecting part of urinary tract: collecting ducts, bladder, etc.
What is the basement membrane composed of? On which stain is the basement membrane visible?
- extra-cellular proteins such as collagen IV and fibronectin
- PAS stain needed to see it
What are tight junctions? What is their function?
Band-like fusions between cells which are impervious to most molecules.
Prevents diffusion between cells.
What are desmosomes? What is their function and where are they found?
Plaques that connect the cytoskeletons of adjacent cells, spreading forces across several cells.
Found in epithelia exposed to abrasive forces.
What are gap junctions? What is their function?
Electrical junctions that permit the transfer of small molecules (e.g. ions) between adjacent cells.
Electrically couple adjacent cells.
