2.3 Epithelial cells and tissues Flashcards
What are 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 ECM (extra cellular matrix) ?
- material deposited by cells that forms the insoluble part of the extracellular environment
- generally composed of fibrillar proteins (e.g. elastin/collagen) embedded in hydrated gel (proteoglycans)
- May be poorly organised (e.g. loose connective tissue) or highly organised (e.g. tendon, bone, basal lamina)
What are the 5 main cell types?
- Connective tissue cells
- Contractile tissues
- Haematopoietic cells
- Neural cells
- Epithelial cells
What is are epithelial cells?
cells forming continuous layers, these layers line surfaces and separate tissue compartments and have a variety of other functions.
What tumour types are there and which tissues are they from?
- carcinomas- epithelial
- sarcomas- mesenchymal (connective tissue and muscle)
- leukaemias- haematopoietic cancer of bone marrow cells
- lymphomas- haematopoietic cancer of lymphocytes
- neuroblastomas- neural cell cancers of neurones
- gliomas- neural cell cancers of glial cells
How are epithelial cells and tissues organised?
- epithelial cells make organised, stable cell-cell junctions to form continuous + cohesive layers
- epithelial layers line internal and external body surfaces and have a variety of functions e.g. transport, absorption, secretion, protection
- cell-cell junctions key to formation and maintenance of epithelial layers
What are the 2 main criteria of epithelial classification?
their shape:
- squamous (flattened plate-shape)
- cuboidal
- columnar
their layering:
- single layer = simple epithelium
- multi-layered = stratified epithelium
Epithelial shapes?
squamous (flattened plate-shape)
cuboidal
columnar
Epithelial layering types?
- single layer- simple epithelium
- multi-layered- stratified epithelium
What are the two main types of stratified squamous epithelium?
Keratinising
Non keratinising
keratinising? (Epithelial cell types stratified squamous)
Produce keratin and die, becoming thicker and stronger protective structures (e.g. epidermis- skin epithelium) that protect underlying tissues from various physical and chemical insults e.g. heat, cold, solvents (alcohol), abrasion etc
They lose their cellular organelles and nuclei and aren’t visible under light microscope
Non keratinising? (Epithelial cell types stratified squamous)
Don’t undergo keratinisation and retain nuclei and organelles
e.g. epithelium lining the mouth, oesophagus, anus, cervix and vagina
What does pseudo-stratified mean?
Pseudo means false and the epithelium appears to be multi-layered
However on close examination, the surface cells have contact with the basal lamina
Where are pseudo stratified epithelium found?
airway (trachea and bronchi) epithelium, various ducts in urinary and reproductive tracts
How are transporter epithelial cells specialised?
- Their apical plasma membranes have high concs of ion transporters
- Mitochondria are concentrated at basal aspect of cell, close to extensive basal membrane infoldings which provides energy for active transport across the membranes
- Infoldings increase the amount of basal membrane that can pump ions and water
How are absorptive epithelia specialised?
Carriers transporting nutrients etc are found on brush-border membranes e.g. absorptive intestinal cells (enterocytes), kidney proximal tubule cells
Small intestine SA is increased as it’s long and the interior wall surface is folded into numerous villi that are covered with intestinal epithelial cells
SA further increased by microvilli- plasma membrane projections of the villi
How do nutrients cross brush border?
The BB contains large amounts of active transporters and channels for the uptake of nutrients from the lumen of the gut. As the concentration of nutrients increases in the cytoplasm of the absorptive cells, it diffuses down its concentration gradient into the basal interstitial space to be collected in the capillaries and distributed in the circulation.
How are secretory epithelia specialised?
Secretory epithelium is often arranged in tubules and glands of varying complexity.
Alternatively in many epithelial tissues, individual, dispersed secretory cells can be present in the epithelium.
What is exocrine secretion?
Secretion into a duct or lumen
What is endocrine secretion?
Secretion into the bloodstream
How are organelles in exocrine secretory cells arranged?
The organelles are arranged for secretion from the apical plasma membrane
Where do endocrine cells secrete their contents?
Basal aspect
Secretory vesicles are positioned so that their contents have close access to the blood circulation when released.
What are the domains of a typical epithelial cell?
Top apical domain at the lumenal (open) surface and a bottom basolateral domain in contact with the ECM
The membrane between these 2 surfaces where membranes of adjacent cells touch is the lateral membrane
What is epithelial polarity and what’s it needed for?
different regions of the cell surface are different from one another with organised cellular contents
Needed to give the directionality needed for epithelial function
