Epithelial Cells And Tissues Flashcards
What are the levels of organisation?
Cells Tissues Organs Organ systems Organism
What is a tissue?
A group of cells whose type, organisation and architecture are integral to its function
Made up of cells, ECM and fluid
What are the 5 main cell types?
Connective tissue cells:
Fibroblasts, chondrocytes, osteocytes
Contractile tissues:
Skeletal, cardiac and smooth muscle
Haematopoietic cells:
blood cells, cells of the bone marrow from which they are derived
Neural cells:
Neurones and glial cells
Epithelial cells:
Form continuous layers
How are epithelial cells organised?
They form stable cell-cell junctions to form continuous cohesive layers
These are key to the formation and maintenance of epithelial layers
What are some functions of epithelial layers?
Line internal and external body surfaces
Transport
Absorption
Secretion
Protection
What are possible shapes of epithelial cells?
Squamous (flattened plate shape)
Cuboidal
Columnar
What are the possible layering options of epithelial layers?
Single layer = simple epithelium
Multi layer = stratified epithelium
What is simple squamous epithelium?
Found in alveoli, mesothelium, endothelium lining blood vessels
Usuaally thin for gas exchange
Where is simple cuboidal epithelium found?
Linings found in ducts
E.g. collecting ducts of kidney
Where is the simple columnar epithelium found?
Surfaces involved in the absorption or secretion of molecules
E.g. enterocyted lining the gut
What are the two main types of stratified squamous emithelium?
Keratinising
Cells that produce keratin and in doing so die and become thicker, stronger and protective
Eg epidermis
These cells lose their organelles and nuclei
Non-keratinising
Retain their organelles
Eg epithelium lining the mouth, oesophagus, anus, cervix and vagina
What is pseudo stratified epithelium?
Appears stratified
But the surface cells have contact with the basal lamina
Eg in the trachea epithelium
What are the three areas (domains) of the epithelial membrane?
Apical (top)
Basolateral (bottom)
Junctions (joining)
Why is polarity of the epithelium required?
Most functions of the epithelium are directional.
Polarity means that things will move in the desired direction
For example in excretion of molecules
What are the 4 types of Cell-cell junctions in epithelia?
Tight junctions (apical) Seals the gaps between cells
Adherens junction
Desmasomes (spot junctions)
Mechanically tough
Gap junctions
Channel forming, allowing exchange of materials
How are transporting epithelia adapted to carry out their function?
High concentrations of ion transporters
Lots of mitochondria near basal membrane to provide energy for active transport
Lots of folding for surface area to volume ratio
Coz there is a direction the apical transport happens passively
How are absorptive epithelia adapted to carry out their function?
Transport nutrients
Such as in brush border membranes (eg enterocytes)
Finger like projections (villi) increase SA:V
And micro Villi
Also have goblet cells that secrete mucus
How are secretory epithelia adapted to carry out their function?
Individual dispersed secretory cells can be present in the epithelium
Exocrine: Secretory granules bear the apical bit
Extensive RER at the basal end
Golgi
Endocrine: secretory granules at the basal end (near capillary)
RER at apical
Golgi
What is the difference between endocrine and exocrine?
Endo
Into the blood
Exo
Into a duct or lumen
How are the two types of secretory endothelial layers classified?
Constitutive
Secretory vesicles move directly to the plasma membrane as they are formed
Eg production of plasma in hepatocytes
Stimulated
Secretory vesicles are stored in the cytoplasm and only diss with the plasma membrane to release their contents
Eg adrenaline in the medulla
How does epithelial turnover in the small intestine happen?
The cell migrates up the villus epithelium
The crypts of leiberkhun are constantly producing new cells from stem cells
Inhibition of this process (such as during chemo) cause the villi to be flattened
How does epithelial turnover in the epidermis happen? Yep
The top layer is constantly falling off
But these are replaced by new cells being formed in the basal layer
These eventually flatten out and keratinise as they move upwards f
What does increased epithelial cell proliferation cause?
Hyperproliferation
Constant pressure - corns/ hard skin
Papilloma virus - warts
