Epithelial Cells & Tissues Flashcards
What are tissues?
What are tissues made up of?
Tissues = a group or groups of cells whose type, organisation and architecture are integral to its function
Tissues are made up of cells, extracellular matrix and fluid
What is the extracellular matrix?
What is the extracellular matrix composed of?
Describe the organisation of the extracellular matrix
ECM = material deposited by cells which forms the insoluble part of the extracellular environment
ECM is generally composed of fibrillar (/reticular) proteins (e.g collagens, elastin) embedded in a hydrated gel (proteoglycans/ground substance)
ECM may be poorly organised or highly organised
What are the 5 main cell types? Give examples of cells that come under these classifications + definitions
- connective tissue cells: fibroblasts (many tissues), chondrocytes (cartilage), osteocytes
- Contractile tissues: skeletal muscle, cardiac muscle, smooth muscle
- haematopoietic cells: blood cells, tissue resident immune cells, and cells of the bone marrow from which they’re derived
- neural cells: cells of the nervous system, two main types: neurones & glial cells (support cells)
- epithelial cells: cells forming continuous layers, these layers line surfaces and separate tissue compartments and have a variety of other functions
What are cancers derived from the following cell types called?:
- epithelial cancers
- mesenchymal (connective tissue and muscle) cancers
- haematopoietic cancers
- neural cancers
- epithelial cancers: carcinomas
- mesenchymal (connective tissue and muscle) cancers: sarcomas
- haematopoietic cancers: leukaemias (from bone marrow cells) or lymphomas (from lymphocytes)
- neural cancers: neuroblastomas (from neurones), or gliomas (from glial cells)
Describe the organisation of epithelial cells
what do epithelial layers line and what are their functions?
What is the role of cell-cell junctions?
Epithelial cells make organised, stable cell-cell junctions to form continuous, cohesive layers
Epithelial layers line internal and external body surfaces. Functions include: transport, absorption, secretion, protection
Cell-cell junctions key to the formation and maintenance of epithelial layers
What are the two main criteria of epithelial classification and what does the classification relate to?
Two main criteria of epithelial Classification are:
Shape:
- squamous
- cuboidal
- columnar
Layering:
- single layer = simple epithelium
- multi-layered = stratified epithelium
Classification useful as its related to types of epithelial function
Where are simple squamous epithelial cells found?
What is simple squamous epithelium specialised for?
Simple squamous epithelium is found in the lung alveolar epithelium, mesothelium (lining major body cavities), endothelium lining blood vessels + other blood spaces.
Simple squamous epithelium forms a thin epithelium that allows exchange to occur (eg gas exchange in alveoli)
Where is simple cuboidal epithelium found?
Single cuboidal epithelial cells are typical of the linings found in ducts eg lining the kidney collecting ducts
Where is simple columnar epithelium found?
Simple columnar epithelial cells are typical of surfaces involved in absorption and secretion of molecules eg enterocytes lining the gut
What are the two types of stratified squamous epithelium? Describe their cellular contents
Keratinising stratified squamous epithelium: produce keratin, and in doing so die becoming thicker, stronger, protective structures (e.g. epidermis). These cells lose their cellular organelles and nuclei, not visible under light microscopy.
Non keratinising stratified squamous epithelium: epithelial cells that don’t undergo keratinisation. They retain their nuclei and organelles. (E.g. epithelium lining the mouth, oesophagus, anus, cervix and vagina)
In the various layers, the cell shapes vary, the squamous classification relates to the surface cells
How does keratinising epithelium protect underlying tissues from various physical and chemical insults?
Keratinising epithelium can form thick layers that protect underlying tissues from various physical and chemical insults
E.g. heat, cold, solvents (alcohol), abrasion
What is a pseudo stratified epithelium?
Pseudo stratified epithelium appears to be multi-layered
On close examination, the surface cells have contact with the basal lamina
E.g. airway epithelium + ducts in the urinary and reproductive tracts
What are the discrete domains that the membrane of a typical epithelial cell is split into and what are the domains based on?
What are the domains in contact with/facing?
What is the lateral membrane?
Membrane of the epithelial cell is organised into discrete domains by the formation of junctions.
Membrane polarity generates distinct polarity: apical domain at the lumenal (open) surface and basolateral domain. Basal surface in contact with the extracellular matrix.
Lateral membrane is the membrane between the ECM and lumenal surface, where membranes of adjacent cells appose each other.
Why is epithelial polarity essential for epithelial function?
Why is polarity important for cell surface organisation?
Most epithelial functions are directional eg secretion, fluid and solute transport and absorption. These processes are highly organised (not random).
Epithelial polarity is required to give the directionality needed for epithelial function.
Polarity in epithelial cells allows for diff regions of the cell surface to have discretely organised cellular contents.
Epithelial cell specialisations/functions: Transporting epithelia
What do the plasma membranes of transporting epithelia contain high concentrations of?
Explain how the mitochondria of transporting epithelia are specialised for transportation
What provides directionality to the transport of ions and water across epithelial cells?
The plasma membranes of transporting epithelia contain high concentrations of ion transporters.
The mitochondria in transporting epithelia are closely associated with extensive basal membrane infoldings. Mit are concentrated in the basal aspect of the cell. This provides energy for active transport across the membranes. The infoldings in the basal membrane increase the amount of basal membrane that can pump ions and water.
The basal infoldings contain the active transporters, whereas the apical plasma membrane contains passive ion and water channels. Because active transport is mainly confined to the basal membranes, ion and water transport will have directionality.
