Epithelia Flashcards
What are the 4 ways of classifying epithelia?
Shape of cells
Number of layers of cells
Combination of both the shape of cells and the numbers of layers of cells
Function
What is epithelia?
They are cells which line all surfaces of the body, tubes and cavities. They are also responsible for the formation of the boundary between fluid compartments in the body.
What are carcinomas?
Tumors which arise from epithelial cells
What are the different domains in the shape of epithelial cells?
columnar
cuboidal
squamous
What are the different domains in the number of layers of epithelial cells?
simple and stratified
What are the characteristics of simple epithelia?
One layer of cells
all cells are both in contact with the basement membrane and the lumen
located in areas where diffusion/absorption/secretion take place, the thinner the epithelium the faster those processes take place
What are the characteristics of stratified epithelia?
Many layers of cells
basal cells are in contact with basement membrane
apical cells are in contact with lumen
found in areas where there is a need for protection
the thicker the epithelium, the greater the protection against abrasion/infection/caustic content
Example of a location where simple squamous epithelia is found?
Lining of blood vessels, lymphatics and body cavities
Example of a location where simple cuboidal epithelia is found?
Kidney tubules
Example of a location where stratified squamous epithelia is found?
Skin
Example of a location where stratified cuboidal epithelia is found?
Reproductive system
Example of a location where transitional epithelia is found?
Bladder
What are the characteristics of epithelia which carry out exchange functions?
simple epithelia, flattened, have pores between cells which permit easy passage of molecules (eg. lungs and blood vessels)
What are the characteristics of epithelia which carry out transporting functions?
simple epithelia, are cuboidal or columnar, have tight junctions which limit movement between cells (eg. intestine and kidney)
What are the characteristics of epithelia which carry out ciliated functions?
simple epithelia, cubiodal or columnar, have cilia which move fluid across the surface (eg. trachea and female reproductive tract)
What are the characteristics of epithelia which carry out protective functions?
contain many layers, flattened surface and polygonal beneath, cells tightly connected by desmosomes (eg. skin and mouth)
What are the characteristics of epithelia which carry out secretory functions?
can be simple or many layers, can be columnar or polygonal, can have extensive rough ER or smooth ER, (eg. endocrine or paracrine)
Properties of simple squamous epithelia?
Composed of a single layer of flattened cells which are all very thin with a central nucleus. Looks like a pavement arrangement with irregular shape. All the cells lie near each other with no gaps in between.
What are the 3 levels of folding to increase surface area in simple columnar epithelia?
Large folds:
Microscopicvili
Microvili
What surface modifications can be found in epithelia in small intestine?
Apical surface of each cell is covered by manymicroviliwhich forms a “brush border” which the mucus can stick to
Goblet cells with intensely staining mucus is released to lubricate gut contents
Basement membrane which separates the epithelial cells from tissue underneath
What is the function of cilia in the columnar epithelia in the respiratory tract?
Cilia act like a conveyer belt. The body uses it to move pathogens/pollutants/dust alongcellin order to get rid of it, not involved in diffusion, acts as protection.
Properties of stratified squamous epithelia?
Consists of flattened cells which are worn off and then shed from the surface in a process called desquamation. Basal cells found on the basement membrane undergo cell division and migrate towards the surface.
The function is the protect underlying tissues from abrasion.
Properties of stratified keratinised epithelium?
Flat cells (squamous) subject to abrasion, resists water loss, makes skin waterproof
Properties of transitional epithelia found in bladder?
Containsmanythick layers of stratified epithelium.Able to change shape, distend, when filled with urine.Abundance of many tight junctions prevent the leakage of urine from the bladder into the tissues.
Function of gap junctions?
communication by membrane protein connexin
Function of tight junctions?
occluding by membrane proteins claudin and occludin and actin
Function of desmosomes and hemi-desmosomes?
anchoring
Different roles of tight junctions?
barrier: divides compartments
fences: maintains asymmetric distribution of lipids and proteins in apical and basal membranes, creates membrane domains(keeps proteins in right domains)
Gates: allows some molecules to flow easier than others (selective), allowsabsorptionand/or secretion
Sealing strands: contain major proteins claudin andoccludins, multiple sealing strands increase effectiveness in keeping apical and basal domains completely separated.
2 types of transport
transcellular: through cells
paracellular: between cells
What structures does haemotoxylin stain?
Negatively charged structures (DNA/RNA)
What structures are stained by PAS staining?
Saccharide structures of glycoproteins
Role of simple squamous epithelium in body cavities (mesothelium)?
Selective barrier for passage of immune cells and fluid
Role of simple squamous epithelium in blood vessels (endothelium)?
Selective barrier for diffusion of metabolites and gases and passage of immune cells
What epithelium lines the GI tract?
modified columnar
Surface modifications of lining of GI tract?
absorptive cell microvilli and secretory ability of secretion of mucus
What type of epithelium lines bronchi and trachea?
pseudostratified epithelium, contains cilia and mucus secretion
What is the difference between exocrine and endocrine glands?
Exocrine: secrete onto a body surface
Endocrine: secrete into bloodstream
