Epithelia cells and tissues Flashcards
What is a tissue?
a group or groups of cells whose type, organisation and architecture are integral to its function
What is a tissue made up of?
extracellular matrix and fluid
What are the 5 main cell types?
Connective tissue cells Contractile tissues Haematopoietic cells Neural cells Epithelial cells
What are connective tissue cells?
fibroblasts (many tissues), chondrocytes (cartilage), osteocytes (bone)
What are contractile tissue cells?
skeletal muscle, cardiac muscle, smooth muscle
What are Haematopoietic cells?
blood cells, tissue-resident immune cells, and the cells of the bone marrow from which they are derived
What are neural cells?
cells of the nervous system having two main types; neurones (carry electrical signals) and glial cells (support cells)
What are epithelial cells?
cells forming continuous layers, these layers line surfaces and separate tissue compartments and have a variety of other functions
What are carcinomas?
epithelial cancers
What are sarcomas?
mesenchymal (connective tissue and muscle) cancers
What are lymphomas?
or leukemias?
haematopoietic cancers
What are neuroblastomas or gliomas?
neural cell cancers
What is the function of epithelial cells?
transport, absorption, secretion, protection
What is key to the formation and maintenance of epithelial layers?
cell-cell junctions
how are epithelial cells classified?
their shape
their layering
how are epithelial cells classified by their shape?
squamous (flattened plate-shape)
cuboidal
columnar
how are epithelial cells classified by their layering?
single layer = simple epithelium
multi-layered = stratified epithelium
Where is the single squamous epithelium found?
lung alveolar (air sac) epithelium, mesothelium (lining major body cavities), endothelium lining blood vessels and other blood spaces). THIN
Where is the simple cuboidal epithelium found?
in ducts
e.g. those lining the kidney collecting ducts
Where is the simple columnar epithelium found?
typical of surfaces involved in absorption and secretion of molecules
-enterocytes(lining the gut)
What are the 2 main types of stratified squamous epithelium?
Keratinizing
Non-keratinizing
What is keratinizing Stratified squamous epithelium?
(loose organelles and nuclei) not visible under light microscopy
Epithelial cells which produce keratin and in doing so die becoming thicker, stronger, protective structures
Where is keratinizing stratified squamous epithelium found?
epidermis (skin epithelium)
What is non-keratinizing Stratified squamous epithelium?
Epithelial cells which do not undergo keratinisation. They retain their nuclei and organelles
Where is non-keratinizing stratified squamous epithelium found?
epithelium lining the mouth, oesophagus, anus, cervix and vagina
What is pseudo-stratified epithelium?
appears to be multi-layered
– On close examination, the surface cells have contact with the basal lamina
Where is pseudo-stratified epithelium found?
. airway (trachea and bronchi) epithelium, various ducts in the urinary and reproductive tracts
Why is epithelial polarity required?
to give the directionality needed for epithelial function
What are transporting epithelia?
transport ions and fluids across epithelial layers
What is polarised in the transporting epithelia?
pumps and channels
active Na+/ K+ exchanger
only pumping in one aspect of plasma membrane?
What is required for secretion from transporting epithelia?
polarity
most epithelia secrete in one direction only
What are the 4 main cell-cell junctions in epithelia?
tight junction
adherens junction
desmosomes
gap junction
Where are the tight junctions?
form a belt usually around the apical lateral membrane
What is the role of tight junctions?
sealing gaps between cells
What is the role of adherens junctions?
controls the formation of all others
What are desmosomes?
form mechanically tough junctions between cells
What is the role of desmosomes?
important in tissues required to resist mechanical stresses
What is a gap junction?
channel forming junction
What is the role of the gap junction?
form pores between cells and allows cells to exchange and share materials
What are mitochondria typically associated with?
extensive basal membrane infoldings, providing energy for active transport across the abundant membranes
The infoldings increase the amount of basal membrane that can pump ions and water
How is the small intestine surface area increased?
it is long, and also by the interior surface of the wall of the small intestine being folded into numerous finger-like processes that point into the interior: the villi (covered with intestinal epithelial cells)
What are microvilli?
plasma membrane projections of the villi
Where are carriers transporting nutrients typically found on the microvillus?
brush-border membranes,
e.g. absorptive intestinal cells (enterocytes) and kidney proximal tubule cells
What are the 2 main types of secretion?
exocrine (into a duct or lumen) and endocrine (into the bloodstream)
Where do endocrine cells secrete their contents?
into the basal aspect
– secretory vesicles are positioned so that when their contents are released, they have close access to the blood circulation
What are the 2 classes of endothelial cells (by the way they secrete)?
constitutive
stimulated
What are constitutive endothelial cells?
secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents
example of constitutive endothelial cells?
production of plasma proteins by hepatocytes (constitutive endocrine secretion).
What are Stimulated endothelial cells?
secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents
example of Stimulated endothelial cells?
release of adrenaline from cells of the adrenal medulla after a fight-or-flight stimulus (stimulated endocrine secretion); when stomach contents enter the duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts (stimulated exocrine secretion)
When calls migrate up the villus epithelium, new cells are made by what?
crypt stem cells
What happens when the proliferation of intestinal crypt cells are inhibited?
eg. cancer chemotherapy
results in loss of the finger-like intestinal villi and flattening of the intestinal mucosa. This is responsible for many of the gastro-intestinal disturbances that are side-effects
how are keratinising squamous epithelial cells formed?
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
What does hypoproliferation of epithelial cells result in?
increased cell numbers and a thickening of cell layers
- in response to repeated or constant pressure
What happens if the cell production is greater than the cells lost from the surface?
cells will accumulate creating an increased thick hard layer
What does papilloma virus do?
induces hyperproliferation
– by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation, which results in a surface growth, e.g. a wart
