Epithelia Flashcards
What is the relationship between epithelial function and breast cancer?
Caused by abnormal proliferation of epithelial cells
What is the relationship between epithelial function and cystic fibrosis (CF)?
Caused by defective epithelial chloride ion transport
What is the relationship between epithelial function and cholera?
Caused by enhanced activation of epithelial chloride ion transport in GI tract
What is the relationship between epithelial function and atherosclerosis?
Caused by superficial injury to epithelial lining of blood vessels > atherosclerosis
What are epithelia?
+ Cells that cover or line all the body surfaces, tubes and cavities
+ Cells that form the interfaces between different physiological fluid compartments
- skin (blood tissues and environment)
- blood vessel wall (blood and tissues)
- gut wall (gut and blood)
- lungs, alveoli (air and blood)
What are characteristics of epithelia?
+ Cells in intimate contact with each other and may be connected by tight junctions
+ Epithelial cells are separated from underlying tissues by the basement membrane (BM)
+ Cells undergo rapid division to replace those continually lost from the surface
What is the term for tumours that develop from epithelial cells?
Carcinoma
What are the basic features of epithelial cells?
+ Apex
+ Base
+ Basement membrane (BM)
What are the different shapes of epithelial cells?
+ Squamous
+ Cuboidal
+ Columnar
What are features of simple epithelia?
+ 1 layer of cells
+ All cells in direct contact with lumen and BM
+ Found at sites in the body where there is:
- diffusion
- absorption
- secretion
What are features of stratified epithelia?
+ Multiple layers of cells
+ Cells in contact with BM = basal
+ Cells in contact with apex = apical
+ Found at sites of the body where there is need for protection
What is the advantage of thin epithelium?
The thinner the epithelium, the quicker diffusion or absorption can occur
What is the advantage of thick epithelium?
The thicker the epithelium the greater the protection from abrasion, infection or caustic content
Where can simple squamous epithelium be found?
Blood vessels
Where can simple cuboidal epithelium be found?
Kidney tubule
Where can simple columnar epithelium be found?
GI tract
Where can stratified squamous epithelium be found?
Skin
Where can stratified cuboidal epithelium be found?
Reproductive system
Where can pseudostratified columnar epithelium be found?
Respiratory system
Where can transitional epithelium be found?
Bladder
What are the functions/features of epithelium typically found in the lungs and blood vessels?
+ 1 Cell layer
+ Squamous/flattened
+ For exchange
+ Pores between cells permit easy passage of molecules
What are the functions/features of epithelium typically found in the intestine (GI) and kidneys?
+ 1 cell layer
+ Cuboidal/columnar
+ For transporting
+ Tight junctions limit movement between cells
What are the functions/features of epithelium typically found in the trachea and the female reproductive tract?
+ 1 cell layer
+ Cuboidal/columnar
+ Ciliated
+ Cilia move fluid across surface
What are the functions/features of epithelium typically found in the skins and the mouth?
+ Multilayered
+ Squamous/flattened on the surface: polygonal in deeper layers
+ Protective
+ Cells tightly connected by many desmosomes
What are the functions/features of epithelium typically found in the exocrine (pancreas and salivary glands) and the endocrine (thyroid)?
+ 1 cell layer/multilayered
+ Columnar/polygonal
+ Secretory
+ Extensive rough ER (proteins) or smooth ER (steroids)
What are features of simple squamous epithelium?
+ Simple layer of flattened cells
+ Individual cells are very thin with a central nucleus
+ Pavement-like appearance of the cells
+ Irregular shape
+ Close proximity to each other (no gaps)
What is the term for the epithelium that line the cavities of the body (serous membranes)?
Mesothelium
What is the term for the epithelium that line blood vessels?
Endothelium
What are features of simple columnar epithelium?
+ Apical surface of each cell is covered by several hundred microvilli forming the brush border to which mucus adheres
+ Goblet cells with intensely staining mucus released to lubricate gut contents
+ Basement membrane (BM) separates the epithelial cells from the underlying tissues
In epithelium with goblet cells, what stains the mucus purple/red?
PAS stain for glycoproteins
What are the features of stratified squamous epithelium?
+ Flattened cells that are worn off and shed from the surface by desquamation
+ Basal cells on the BM divide and move upwards to the surface
+ Protects underlying tissues from abrasion
+ Characteristic of wet epithelia subject to abrasion but not dehydration e.g
- mouth
- vagina
- anal canal
What are features of stratified, squamous, keratinised epithelium?
+ Resists water loss (dry)
+ Subject to abrasion
+ Dead squamous cells containing keratin undergo desquamation from the surface
What are features of transitional epithelium in the bladder?
+ Many layers thick
+ High number of tight junctions to prevent leakage of urine from bladder into tissues
What is the difference between non-epithelial and epithelial cells? I’m
Epithelial Cells:
\+ Tight junctions \+ Basement membrane \+ Apical membrane \+ Baso-lateral membrane \+ Basal membrane
What are the different types of cell-cell junctions?
+ Gap junction
+ Tight junction
+ Adhering junction
+ Desmosome
What are the different types of cell-matrix junctions?
+ Hemi-desmosome
+ Focal adhesions
Features of gap junctions?
+ Communication
+ Connexin (membrane protein)
Features of tight junctions?
+ Occluding
+ Occludin, claudin (membrane protein)
+ Actin (cytoskeleton fibre)
Features of adhering junctions?
+ Anchoring
+ Cadherin (protein membrane)
+ Actin (cytoskeleton fibre)
Features of desmosomes?
+ Anchoring
+ Cadherin (membrane protein)
+ Intermediate filaments (cytoskeleton fibre)
Features of hemi-desmosomes?
+ Anchoring
+Integrin (membrane proteins)
+ Keratin (cytoskeleton fibre)
+ Laminin (extracellular matrix protein)
Features of focal adhesions?
+ Anchoring
+Integrin (membrane proteins)
+ α-actin (cytoskeleton fibre)
+ Laminin (extracellular matrix protein)
What are the different compartments of epithelial cells
+ Apical compartment
+ Basal compartment
What are the ways in which molecules can cross the epithelial barrier?
+ Trans-cellular transport
- secretion
- absorption
+ Paracellular movement
What are sealing strands?
Major tight junction proteins (claudins, occludins)
What are the roles of tight junctions?
+ Barriers
- separate one compartment from another
+ Fences
- Maintain the asymmetric distribution of lipids and proteins in the apical and basal membranes
+ Gates
- allow some molecules to flow more easily than others
What do tight junctions in epithelial cell layers do?
- Create a barrier between different compartments
2. Allow the processes of absorption and/or secretion to create compartments with different molecular compositions
Which type of epithelium will allow rapid diffusion?
Simple squamous epithelium
Which type of epithelium is vulnerable to damage?
(Stratified) keratinised epithelium
Which type of epithelium will give more protection?
Stratified squamous epithelium
Which epithelium will be more of a barrier to infection?
Thicker epithelium
- stratified
- columnar
Which type of epithelium have a secretory function?
+ Pseudostratified, ciliated, columnar interspersed with goblet cells
+ Stratified squamous (with goblet cells) from
