Epithelial Cells Flashcards
What are tissues
A group or groups of cells whose type, organisation and architecture are integral to its function. Madeup of cells, extracellular matrix and fluid.
Large number of cells can be grouped into 5 major categories
Haemopoietic, Epithelial, Contractile, Connective tissues and neural cells
Epithelial cancers
Carcinomas
Mesenchymal cancers( connective tissue and muscle)
Sarcomas
Haemopoietic cancers
Leukaemias ( from bone marrow cells) or lymphomas (from lymphocytes)
Neural cell cancers
Neuroblastomas or gliomas
Functions of epithelial cells
Transport, absorption, secretion and protection
Squamous
Flattened, plate shapes
Columnar
Arranged in colums
Cuboidal
Cube-like
Single layer
Simple epithelium
Multi layer
Stratified epithelium
simple squamous epithelium
Lung alveolar epithelium, mesothelium (lining major body cavities) , endothelium lining blood vessels and other blood spaces). Forms thin epithelium allowing exchange to occur
Simple Cuboidal epithelium
Linings of ducts e.g. kidney collecting ducts
Simple Columnar epithelium
Absorption and secretion of molecules ( enterocytes lining the gut, involved n the take up of the breakdown products)
Stratified squamous epithelium
Two types:
Keratanizing: produce keratin and die in doing so and become much thicker and stronger structures (e.g. skin epithelium). Such cells lose their celullar organelles and nuclei which are not visible under light microscopy
Non-keratanizing: retain nuclei and organelles. (e.g. epithelium lining the mouth, oesophagus, anus, cervix and vagina)
Pseudo-stratified epithelium
Appears to be multi-layered but on close examination, the surface cells have contact with basal lamina, e.g. airway(trachea and bronchi) epithelium, various ducts in the urinary and reproductive tractd
Read the notes on epithelial cell polarity on onenote
read the notes on epithelil cell polarity on onenote
Different types of cell-cell junctions in epithelia
Tight junction, cell-cell anchoring junction , channel-forming junction and cell-matrix anchoring junction
Examples of cell-cell anchoring junctions
Adherens and desosomes
example of channel-forming junction
gap junction
example of cell-matrix anchoring junctions
actin-linked cell-matrix junction (anchors actin filaments in a cell to extracellular matrix) and hemidesomosome (anchors intermediate filaments in a cell to extracellular matrix)
function of tight junctions
usually form a belt usually arounf the apical lateral membrane. Involved in sealing the gapd beteween cells.
adherens junctions
Just below tight junction- basically master junction which controls the formation of all the other junctions
desmosomes
scattered through the lateral membrane . These are spot junctions that form mechanically tough junctions between cells and are important in tissues that require to resist mechanical stresses.
gap junction
channel forming juncion. Usually forms pores between cells and allows cells to exchange and share materials- help cells in synchronizing activities.
features in transporting epithelial cells
Plasma membrane contains high concs of ion transporters. Normally, mitochondria are closely associated with extensive basal membrane infoldings , providing energy for AT . Infoldings increase the amount of basal membrane that can pump ions and water.
Apical plasma membrane has many ion and water channels for passive transport of water and ions
Absorptive epithelium
Carriers transporting nutrients are found on brushborder membrane (columnar or cuboidal membrane), e.g. absorptive intestinal cells (enterocytes) and kidney proximal tubule cells.
Secretory cells (goblet cells secreting mucus)
Active transporters and channels for the uptake of nutrients
where is the secretory epithelium found
epithelium is arranged into tubules and glands.
2 main types of secretion: exocrine(into duct/lumen) and endocrine (into the bloodstream)
where are the secretory granules positioned in the exocrine and the endocrine cells
Exocrine: positioned towards apical cytoplasm as they are arranged for secretion from the apical plasma membrane
where are the secretory granules positioned in the endocrine cells
towards the basal aspects so that when their contents are released, they have close access to blood circulation
2 ways to classify endothelial cells on the way they secrete
constitutive : secretory vesicles as they are formed move directly to the plasma membrane and release their contents, e.g. production of plasma proteins by hepatocytes
stimulated: secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents, e.g. the release of adrenaline from cells of adrenal medulla after a fight-or-flight stimulus (stimulated endocrine secretion)
inhibition of epithelial turnover in the small intestine (intestinal crypt cells)
Cancer chemotherapy - reults in loss of finger like villi and flattening of intestinal muscosa. Responsible for many of gastro-intestinal disturbances that are side -effects of chemotherapy. 5-FU example of drug
Epithelial turnover in the epidermis (keratinising squamous epithelium of body)
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 keratanising. Each layer replaces the one above as the layers are lost from the surface
Hyperproliferation of epithelial cells
Results in increased cell numbers and a thickening of cell layers. Can be in esponse to repeated or constant pressure. If increase in cell production is greater than cell loss , cells will accumulate creating a thick, hard layer/corn.
Papilloma virus can induce hyperproliferation - do this by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation
