Molecular Biology - Epithelial cells/tissues Flashcards
System hierarchy
Cells - tissues- organs - organ systems - organism
Tissue
Group or groups of cells whose type, organisation and architecture are integral to its function
Extracellular matrix
Material deposited by cells which forms the insoluble part of the extracellular environment - composed of fibrillar proteins embedded in hydrated gel
Epithelial cells
Form continuous layers which line ad separate tissue compartments
5 main cell types
Connective tissue cells - chrondocytes etc
Contractile tissue - cardiac/skeletal muscle
Haematopoietic cells - blood cells
Neural cells - neurones and glial cells (support)
Epithelial cells
Carcinomas
Derived from epithelial cells
Sarcomas
Connective tissue/muscle cancers
Leukaemias (bone marrow) /lymphomas (lymphocytes)
Haematopoietic cancers
Neuroblastomas
Neural cell cancers from neurones
Epithelial cells
Make organised/stable cell-cell junctions to form continuous and cohesive layers
Epithelial layers
Cell-cell junctions are key to the formation and maintenance of epithelial layers
Epithelial classification
Shape
Layer
Shape
Squamous (plate shapes) - flat
Columnar - arranged in columns (long vertically)
Cuboidal - cube like
Layer
Single layer = simple epithelium (alveoli)
Multi-layer = stratified epithelium
Simple squamous found in
Small diffusion distance - alveoli/mesothelium/endothelium ; allows exchange to occur
Simple cuboidal found in
Linings found in ducts
Simple columnar epithelium
Surfaces involved in absoprtion and secretion of molecules (like enterocytes lining the gut)
Keratinizing
Epithelial cells produce keratin - die - become thicker and stronger (like the skin) ; lose their cellular organelles
Non-keratinizing
Retain their nuclei and organelles (epithelium lining mouth, anus etc)
If no nuclei visible
Keratinizing
purpose of keratinizing
Protects tissues from heat/cold/solvents etc
Pseudo-stratified epithelium
Surface layers have contact with basal lamina
Stratified means
NO GAP BETWEEN LAYERS OF CELLS
Epithelial cells functions
Transporting epithelium
Absorptive epithelium
Secretory epithelium
Membrane polarity gives
DIRECTIONALITY
Bottom and top of cell
Bottom = basolateral (attached to basal lamina)
Top = apical domain
State of epithelia
Must be polarised for mass flow to occur
Adaptations for efficient transport
Mnay mitochondria provide a lot of ATP needed for transport across membranes
Greater membrane infoldings = larger surface area to pump
Where are mitochondria located?
Near the basal aspect close to the infoldings which contain active transporters - apex has directionality (passive movement)
Where is active transport confined mainly?
Basal - so ion/water transport has directionality
Absorptive epithelium
Small intestine SA is long + greater with villi etc - found at brush-border membranes
Brush borders
Rich in active transporters and channels for uptake of nutrients
Secretory epithelium
Tubules + glands
Exocrine (into duct/lumen) and ENDOCRINE (into bloodstream)
Exocrine pancreas
Out via pancreatic duct
Endocrine cells secrete tooooo
Basal aspect ; secretory vesicles are positioned for easy access to blood circulation
Apical phase
Enzymes/pancreatic juices exocrine UNLIKE HORMONE BASAL
Turning over of cells?
Cells lost by cell death and are replaced by proliferation of stem cells in epithelium ; balance between cell proliferation and cell death
How does replacement work in turnover of epithelial cells?
Cells in intestinal crypts replace cells lost from tips of the villi?
Cancer drugs what happens?
Drugs inhibit proliferation of crypt cells so = loss of villi and results in GI side-effects
SHORTENED VILLI
Tumour formation
Rate of cell loss not sufficient to maintain tissue volume - creates a benign tumour (adenoma) which has high risk of acquiring mutations that switch to cancerous
Epithelial cell proliferation - epidermis
Proliferate in basal cell layer - lose their organelles and then migrate to surface (keratinising while doing so)
Hyperproliferation of epithelial cells
Increased cell numbers and thickening ; cells will accumulate and create an increased thick hard layer
Papilloma virus
Hijacks cellular machiner and induce proliferation which causes surface growth
Changes to steady state physiologically?
Endometrial epithelial lining during menstrual cycle
Increase during pregnancy in number and size of epithelial glands of breast
