Epithelial Cells And Tissues Flashcards
What are epithelial cells?
Cells which form continuous layers which line surfaces and separate tissue compartments
What is the importance of having well organized and stable cell-cell junctions?
means the cells are not leaky - fully cohesive
What is the importance of epithelial cells?
Separating tissue compartments or lining the surfaces of a tissue
What two features of epithelial cells are used to classify them?
- Shape
2. Size
What do squamous cells look like?
Flattened , plate shaped
What do columnar epithelium cells look like?
Arranged in columns
What do cuboidal epithelium look like?
Cube-like
What are the three classifications of shape in epithelial cells?
Squamous, Columnar and Cuboidal
How many layers do simple epithelium have?
one layer
What is he name given to describe the multilayered appearance of epithelium?
Stratified
Where are simple squamous epithelium found?
Found in lung alveolar, epithelium, mesothelium and endothelium
What is the purpose of simple squamous epithelium?
form a thin epithelium that allows gas exchange to occur
Which surfaces are simple columnar epithelium found in?
Surfaces involved in absorption and secretion of molecules eg enterocytes lining the gut or surfaces involved in the uptake or breakdown of product of digestion
What are the two types of stratified squamous epithelium?
Keratinizing and Non-keratinizing
What is meant by non-keratinizing epithelium?
epithelial cells which do no undergo keratinisation and so retain their nuclei and organelles
Where are non-keratinizing stratified squamous epithelium found?
epithelium lining the mouth, oesophagus, anus, cervix and vagina
What is meant by keratinizing epihelium?
Epithelial cells which produce keratin
What happens to cells after they produce keratin?
The cells produce keratin and then die - becomes much stronger surfaces e epidermis - lose their organelles and nuclei
What is the benefit of the keratinizing ability of some stratified squamous epithelium?
can form thick layers which are useful for protecting underlying tissues for various physical and chemical insults eg heat, cold, solvents (alcohol) and abrasion
What is meant by pseudo-stratified epithelium?
This epithelium appears to be multi-layered but on close examination, all th surface cells have contact with the basal laminae
Where are pseudo-stratified epithelium found?
Airway (trachea and bronchi) epithelium, various ducts in the urinary and reproductive tracts
What are tissues made up from?
Cells, extracellular matrix and fluid
What organises tissues into discrete domains?
Junctions
Where is the apical domain found?
At the lumenal surface
What is the basolateral domain in contact with?
The basal laminae
Why is polarisation of secretory epithelium so essential?
To ensure that contents are secreted in the right direction - otherwise could result in the secretion of substances which would harm our own tissues
What is meant by polarity in epithelial cells?
different regions of the cell surface being different from one another with discretely organised cellular compartments
What is epithelium polarity so essential for?
Ensuring that in specialised epithelium like those involved in transport or secretion - that the process occur in a specific and intended direction
What would happen in transporting epithelium if there was no polarisation?
lack of directional flow, and ions would be pumped across both sides
What are the four types of junctions seen between epithelial cells?
- Adherens junctions
- Tight Junctions
- Desmosomes
- Gap junctions
What do tight junctions do?
Seals the gap between cells
What do adherens junctions do?
Master junction which controls the formation of the other three junction types
What go gap junctions do?
They are channel forming junctions which form pores betwen cells to allow communication and the exchange of materials
What do desmosomes do?
Form mechanically tough junctions between cells that are important in tissues to allow them to resist mechanical stress
What are the three types of specialised epithelium which can be found?
- Absorptive
- Secretory
- Transporting
Describe how transporting epithelium are adpated to their function?
The plasma membrane contains high concentrations of ion transporters
Basal membrane as extensive folding in order to provide alot of energy for active transport across the membranes
Where are infoldings found in transporting epithelium?
In the basal membrane
Why are there alot of mitochondria near the basal membrane in transporting epithelium?
In order to provide energy for the active transport of substances
How is directionality achieved in transporting epithelium?
The mitochondria provide the ATP required for active transport at these membranes. Because active transport is mainly confined to the basal membranes, ion and water transport will have directionality.
What increases the surfac area for absoprtion in the small intstine?
presence of villi - foldings of the small intestine into finger like projections
what are microvilli?
Plasma membrane projections of the villi
What can be found to be interspersed among the absorptive cells of the intestinal villi?
secretory cells (goblet cells secreting mucus)
Where are carriers transporting nutrients found?
Carriers transporting nutrients are typically found on the microvillous brush-border membranes, e.g. absorptive intestinal cells (enterocytes) and kidney proximal tubule cells.
What does the brush border contain?
The BB contains large amounts of active transporters and channels for the uptake of nutrients from the lumen of the gut.
Describe how substances are absorbed into circulation?
As the concentration of nutrients increases in the cytoplasm of the absorptive cells, it diffuses down its concentration gradient into the basal interstitial space to be collected in the capillaries and distributed in the circulation.
What are the two main types of secretion?
Exocrine and endocrine secretion
How does the pancreas display both endocrine and exocrine functions?
Exocrine = into ducts - secretes pancreatic enzymes and pancreatic juice into ducts
Endocrine = into blood - secretes hormones from the islet cells
Describe the organisation of an exocrine secretory cell/
Have extensive RER in the basal cytoplasm, then glgi on top of that and secretory granules in the apical cytoplasm in order to secrete from the apical plasma membrane
Describe the organisation of an endocrine cell?
Extensive Rough RER in the apical cytoplasm and secretory granules in the basal cytoplasm - positioned so that when their contents are released, they have close access to the blood circulation.
What is meant by constitutive secretion?
secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents, e.g. production of plasma proteins by hepatocytes (constitutive endocrine secretion).
What is meant by stimulated secretion?
secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated
What is an example of stimulated endocrine secretion?
the release of adrenaline from cells of the adrenal medulla after a fight-or-flight stimulus
What is an example of stimulated exocrine secretion?
when stomach contents enter the duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts
Describe the process of epithelial proliferation?
Many epithelia are constantly “turning-over”, i.e. cells that are lost by cell death or by mechanical removal (e.g. abrasion) are replaced by the proliferation of stem cells within the epithelium.
How are cells lost from the tips of intestinal villi lost?
Cells in intestinal crypts
How are cells lost from the surface of stratified squamous epithelium replaced?
Cells of the basal layer of stratified squamous epithelia divide to replace cells lost from the surface.
where are new cells produced in the small intestine?
in the crypt of Leiberkhun
What are the effects of chemotherapy on epithelial cells?
Inhibition of the proliferation of intestinal crypt cells, e.g. in cancer chemotherapy, results in loss of the finger-like intestinal villi and flattening of the intestinal mucosa.
Describe the epithelial turnover in the epidermis?
surface cells are constantly being lost, but are replaced by new cells being formed in the basal layer which migrate up while undergoing a programme of differentiation that eventually leads to them flattening out and keratinising. Each layer replaces the one above as the layers are lost from the surface.
Which virus can induce hyperproliferation of epithelial cells?
Papilloma virus
what forms if the increase in cell production is greater than cell loss from the surface of the eidermis?
cells accumulate and produce “hard skin” or a corn
