epithelial tissues Flashcards
where are epithelial tissues found?
lining all body surfaces (epidermis) and all internal tubes and cavities
what are the functions of epithelial tissue?
- protective barrier (skin) to prevent substances entering/leaving the body (protects against microbial invasion)
- acts as a continuous boundary between different environments
- provides opportunity to regulate movement of substances
- diffusion in lungs and capillaries
- absorption in the GIT
- secretion in glands/ ducts
what is the general arrangement of epithelia?
continuous sheet of tightly bound cells with lateral surfaces adhered to each other
- epithelial cells are polarised along the apical/basal axis
what is a tight junction?
- epithelial cells create an impermeable seal between adjacent cells to prevent liquid escaping
- this prevents water passage and allows a layer of cells to act as an impermeable barrier
what is an example of a tight junction location?
epithelium lining the bladder to prevent urine leaking into the extracellular space
what are desmosomes?
strong adhering junctions between membranes of adjacent cells, anchoring them together
- they ensure epithelial tissues can stretch while remaining in contact
what are the three ways in which epithelial tissue structure can differ?
- shape
- number of cell layers
- apical specialisations
what are the different shapes of epithelial cells?
- squamous
- cuboidal
- columnar
what are the names for the different number of cell layers in epithelium?
- simple- single layer of cells- selective diffusion/secretion/absorption
- stratified- 2 or more layers of cells
what are the apical specialisations of epithelial cells?
- microvilli
- cilia
- keratin
what do microvilli do to epithelial cells?
increase the apical surface layer
what do cilia do to epithelial cells?
assist the movement of particular matter
what does keratin do to epithelial cells?
adds a strong protective apical layer
what is the function of simple squamous epithelia
lines the surfaces involved in passive diffusion
where is simple squamous epithelia located?
in the lungs (alveoli) and capillaries (where its called endothelium)
what is the function of simple columnar epithelium?
lines small ducts and tubules involved in absorption and secretion
where is simple cuboidal epithelium found?
renal tubes and small ducts of salivary glands
what is the function of simple columnar epithelium?
lines absorptive surfaces
where is simple columnar epithelium located?
small intestine
what is the function of ciliated simple columnar epithelium?
transports ovum from ovary to uterus
where is ciliated simple columnar epithelium located?
the female reproductive tract
where is the apical surface?
faces the external surface
what is the function of simple ciliated pseudostratified columnar epithelium?
propels the surface layer of mucus containing trapped particles towards the pharynx
where is ciliated simple pseudo stratified columnar epithelium located?
airways of the respiratory system
what does pseudo stratified mean?
the nuclei of the cells are at random locations within the cell giving the false impression that there is multiple layers
what are goblet cells?
modified columnar epithelial cells which synthesis and secrete mucus
where are goblet cells found?
scattered throughout simple columnar epithelium- repertory/gastrointestinal
what is the function of stratified cuboidal epithelium?
secretory
where is stratified cuboidal epithelium located?
it is rare- located in some secretory ducts
what is the function of stratified columnar epithelium?
secretory and protective
where is stratified columnar epithelium located?
it is rare- in the male urethra and lining and in some glands
describe stratified squamous epithelia
- gives protection from mechanical abrasion
- cells mature from basal layer from dividing stem cells
- cells migrate to the apical surface layer
- the cells appear cuboidal at the basal layer but are just really active, they are squashed into their known squamous shape as they migrate
where is stratified squamous epithelium located?
the epidermis and oral cavity
what are the two specialisations that stratified squamous epithelium can be?
keratinised or non-keratinised
where does keratin form on epithelium?
the apical surface
what is the function of keratin
enhances resistance to physical stress
- keratin is non living (no nuclei)
where are keratinised epithelium found?
protected surfaces eg epidermis
what is transitional epithelium?
- epithelium which allows for expansion and stretch
- found ONLY in the bladder
how does ulceration occur?
when there is a break in continuity of epithelium
what causes oral squamous cell carcinoma?
dysplastic epithelial cells proliferating in an uncontrollable manner, which destroy and invade adjacent tissues
