Epithelia Flashcards
What is the structure of epithelia tissue?
Epithelia comprise 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 – e.g. skin
Absorption – e.g. gut
Secretion – e.g. pancreas
How many layers in simple and stratified epithelia?
Simple epithelia - Single layer of cells on a basement membrane
Stratified (compound) epithelia - Two or more layers of cells on a basement membrane
What is simple squamous epithelium?
Single layer of flattened plate-like cells on a basement membrane
Parallel oval nuclei
Where is simple squamous epithelium found?
Lines:
Inside of blood vessels - endothelium
Outside of lungs - mesothelium
Abdominal organs - peritoneum
What is simple cuboidal epithelium?
Single layer of cells with similar height and width on a basement membrane
Central spherical nuclei
Where are simple cuboidal epithelium found?
Lines: kidney tubules, small ducts
What is simple columnar epithelium?
Single layer of cells taller than they are wide, on a basement membrane
May or may not have cilia or microvilli
Where are simple columnar epithelium found?
Lines: the stomach, intestines and uterus
What are microvilli?
Microscopic projections on luminal surface of absorptive cells
Where are microvilli found and what do they do?
Intestinal brush border
Increase surface area for absorption of nutrients, water
What is cilia?
Microscopic motile projections on luminal surface of cells
Contain contractile proteins - tubulin and dyenin
Where is cilia found?
Respiratory tract and reproductive tract (fallopian tube)
What is stratified epithelia? Where is it found?
Several layers of epithelia.
Parts where exposed to frequent forces eg skin, mouth, vagina, oesophagus, uterus.
What is stratified non keratinising squamous epithelium?
Multiple layer of squamous epithelium cells on a basement membrane
They don’t produce keratin protein, no need for waterproofing
Mature surface layers are plate-like squames
Where can stratified non keratinising squamous epithelium be found?
Mouth, vagina, oesophagus, oropharynx
What is stratified keratinising squamous epithelium?
Multiple layer of stratified keratinising squamous epithelium cells on a basement membrane
Mature surface layers are plate-like squames
What protein do stratified keratinising squamous epithelium produce? Why? Where is it found?
Keratin.
It creates a waterproof layer
On skin.
What happens to keratin as cell matures?
As cell matures it accumulates more keratin, shown by a layer of dark purple granules, till eventually cells die and left with dead flat plates of keratin.
Thick keratin layers - palms, soles
Thin keratin layers - eyelids
What is pseudo-stratified epithelia?
Single layer of cells of variable height, mimicking multiple layers on a basement membrane
All cells in contact with basement membrane
Has cilia
Where is pseudo stratified epithelia found?
Lines the conducting airways - trachea, nasopharynx
What is urothelium?
Urothelium is specialised stratified epithelium
What is the structure of the urothelium?
Combination of pseudo stratified epithelium +
Surface layer cells - isn’t in contact with basement membrane called umbrella cells
Waterproof - tight junctions
Where is urothelium found?
Lines: collecting part of the urinary tract
What is the basement membrane? What stain can be used to observe it?
Separates bottom layer of epithelia and underlying connective tissue
PAS - Periodic Acid Shift - Dark purple/Magenta
What is basement membrane compose of? What is it essential for?
Composed of extra-cellular proteins - Collagen IV and Fibronectin
Essential for the proper functioning and survival of the epithelium
What the the 3 epithelial junctions?
- Tight junction (occluding)
- Desmosomes (anchoring/adherent)
- Gap junction (communicating)
What is contact inhibtion?
When epithelial cells join with other epithelial cells inhibiting cell growth.
Explain tight junctions:
Band-like fusions between cells that are impervious to most molecules
Prevent diffusion between cells
Explain desmosomes: Where are these found prominent?
Plaques form physical joins between cells and connect the cytoskeletons of adjacent epithelial cells
Mechanical load is spread between several cells instead of one.
Skin
What are hemidesmosomes? Where are they found?
Help cells bind to basement membrane. In basal layer
Explain gap junctions:
Electrical junctions that permit the transfer of small molecules and ions between adjacent epithelial cells
Results in: Electrically couple adjacent cells
