Epithelial Cells And Tissues Flashcards
How do you get from cells to an organism?
cells-> tissues-> organs-> organ systems-> organism
What is a tissue?
A group/ groups of cells whose type, organisation and architecture are integral to its function. Tissues are made up of cells, ECM and fluid
What is the extra-cellular matrix?
Material deposited by cells which forms the “insoluble” part of the EC environment
Generally composed of fibrillar (or reticular) proteins (e.g., collagen, elastin) embedded in a hydrated gel (proteoglycans or “ground substance”)
May be poorly organised (e.g., loose connective tissue) or highly organised (e.g., tendon, bone, basal lamina)
What are the main 3 types of cells and their subtypes?
Connective tissue cells…
Fibroblasts
Chondrocytes
Osteocytes
Neural cells
Epithelial cells
What are neural cells?
Cells of the nervous system having 2 main types; neurones (carry electrical signals) and glial cells (support cells)
What are contractile tissues?
skeletal muscle, cardiac muscle, smooth muscle
What are epithelial cells?
Cells which form continuous layers which line surfaces and separate tissue compartments and have a variety of other functions
What is the importance of having well organised and stable cell-cell junctions?
means the cells are not leaky - fully cohesive
Do tumours retain characteristics of the cell type from which they originate?
Yes
What are epithelial cancers called?
Carcinomas
What are mesenchymal cells (connective tissue and muscle) cancers called?
sarcomas
What are haematopoietic cancers called?
Leukaemia (from bone marrow cells)/ lymphomas if from white blood cells
What are neural cell cancers called?
neuroblastomas and gliomas
How would you describe epithelial organisation and what are their functions (4)?
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 are key to the formation and maintenance of epithelial layers
What two features of epithelial cells are used to classify them?
- Shape
- size
What do squamous cells look like?
Flattened , plate shaped
What do columnar epithelium cells look like?
Arranged in columns
What do cuboidal epithelium look like?
Cube-like
What is the name given to describe one layer appearance of epithelium?
simple
What is he name given to describe the multilayered appearance of epithelium?
Stratified
Where are simple squamous epithelium found?
Found in lung alveolar, epithelium, mesothelium and endothelium
What is the purpose of simple squamous epithelium?
form a thin epithelium that allows gas exchange to occur
Which surfaces are simple columnar epithelium found in?
Surfaces involved in absorption and secretion of molecules eg enterocytes lining the gut or surfaces involved in the uptake or breakdown of product of digestion
Where are simple cuboidal epithelium found?
linings found in ducts e.g., those lining the kidney collecting ducts
What are the two types of stratified squamous epithelium?
Keratinizing and Non-keratinizing
What is meant by non-keratinizing epithelium?
epithelial cells which do no undergo keratinisation and so retain their nuclei and organelles
Where are non-keratinizing stratified squamous epithelium found?
epithelium lining the mouth, oesophagus, anus, cervix and vagina
What is meant by keratinizing epihelium?
Epithelial cells which produce keratin
What happens to cells after they produce keratin?
The cells produce keratin and then die - becomes much thicker, stronger and protective surfaces epidermis - lose their organelles and nuclei (not visible under light microscopy)
What is the benefit of the keratinizing ability of some stratified squamous epithelium?
can form thick layers which are useful for protecting underlying tissues for various physical and chemical insults eg heat, cold, solvents (alcohol) and abrasion
What is meant by pseudo-stratified epithelium?
This epithelium appears to be multi-layered but on close examination, all th surface cells have contact with the basal laminae
Where are pseudo-stratified epithelium found?
Airway (trachea and bronchi) epithelium, various ducts in the urinary and reproductive tracts
What are the 3 types of epithelium?
Transporting
Absorptive
Secretory
What do most epithelial function require?
directionality which comes from plasma membrane polarity
What organises tissues into discrete domains?
Junctions
Where is the apical domain found?
At the lumenal surface
What is the basolateral domain in contact with?
The basal laminae
How do gases cross membranes?
e.g., O2, N2, CO2 and hydrophobic molecules (e.g., steroids) can diffuse across the lipid bilayer
What are the 4 methods of transport across a membrane?
Down an electrochemical gradient:
1. simple diffusion
2. channel-mediated (passive transport)
3. transported mediated (passive transport)
Against an electrochemical gradient:
4. active transport (active transport)
Why is polarisation of secretory epithelium so essential?
To ensure that contents are secreted in the right direction - otherwise could result in the secretion of substances which would harm our own tissues
What is meant by polarity in epithelial cells?
different regions of the cell surface being different from one another with discretely organised cellular compartments
What is epithelium polarity so essential for?
Ensuring that in specialised epithelium like those involved in transport or secretion - that the process occur in a specific and intended direction
What would happen in transporting epithelium if there was no polarisation?
lack of directional flow, and ions would be pumped across both sides
What does the transporting epithelium contain?
tissues with high concentrations of ion transporters in the plasma membranes which contain:
- mitochondria are often closely associated providing energy for active transport across the membranes
- membrane infoldings increase the amount of basal membrane that can pump ions and water
What is the basal lamina near?
The capillary
Where are mitochondria and membrane infoldings concentrated?
the basal aspect of the cell
What do the membrane infoldings contain?
active transporters
What are the four types of junctions seen between epithelial cells?
- Adherens junctions
- Tight Junctions
- Desmosomes
- Gap junctions
Why is it important that mitochondria are at the basal lamina?
Active transport is then mainly confined to the basal membranes, ion and water transport will have directionality
In the absorptive epithelium where are carriers found?
Carriers transporting nutrients are found at brush-border membranes
- e.g., absorptive intestinal cells (enterocytes); kidney proximal tubule
How is the small intestine surface increased?
By being 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
- the villi contain many intestinal epithelial cells
What are the 2 main types of secretion?
Endocrine into bloodstream
exocrine into a duct or lumen
Does the pancreas carry out exo or endocrine functions?
both
What do tight junctions do?
Seals the gap between cells
What do adherens junctions do?
Master junction which controls the formation of the other three junction types
What go gap junctions do?
They are channel forming junctions which form pores betwen cells to allow communication and the exchange of materials
What do desmosomes do?
Form mechanically tough junctions between cells that are important in tissues to allow them to resist mechanical stress
Describe how transporting epithelium are adpated to their function?
The plasma membrane contains high concentrations of ion transporters
Basal membrane as extensive folding in order to provide alot of energy for active transport across the membranes
What can be found to be interspersed among the absorptive cells of the intestinal villi?
secretory cells (goblet cells secreting mucus)
What does the brush border contain?
The BB contains large amounts of active transporters and channels for the uptake of nutrients from the lumen of the gut.
Describe how substances are absorbed into circulation?
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 does the pancreas display both endocrine and exocrine functions?
Exocrine = into ducts - secretes pancreatic enzymes and pancreatic juice into ducts
Endocrine = into blood - secretes hormones from the islet cells
Describe the organisation of an exocrine secretory cell/
Have extensive RER in the basal cytoplasm, then golgi on top of that and secretory granules in the apical cytoplasm in order to secrete from the apical plasma membrane
(away from capillary into duct)
Describe the organisation of an endocrine cell?
Extensive Rough RER in the apical cytoplasm and secretory granules in the basal cytoplasm - positioned so that when their contents are released, they have close access to the blood circulation.
What does turning over mean for epithelia?
Many epithelia are constantly turning over, cells that are lost by cell death or mechanical removal (e.g., abrasion) are replaced by the proliferation of stem cells within the epithelium
What is meant by constitutive secretion?
secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents, e.g. production of plasma proteins by hepatocytes (constitutive endocrine secretion).
What is meant by stimulated secretion?
secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents when stimulated
What is an example of stimulated endocrine secretion?
the release of adrenaline from cells of the adrenal medulla after a fight-or-flight stimulus
What is an example of stimulated exocrine secretion?
when stomach contents enter the duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts
How are cells lost from the tips of intestinal villi lost?
Cells in intestinal crypts
Describe the process of cell proliferation in the epidermis.
Cells of the basal layer of stratified squamous epithelia divide to replace cells lost from the surface.
Surface squame are replaced by new are replaced by new cells formed in the basal alter which migrate to the surface
While migrating, they undergo a programme of differentiation that eventually leads to them flattening out and keratinising
where are new cells produced in the small intestine?
in the crypt of Leiberkhun
What are the effects of chemotherapy on epithelial cells?
Inhibition of the proliferation of intestinal crypt cells, e.g. in 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 of chemotherapy
Describe the epithelial turnover in the epidermis?
surface 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 keratinising. Each layer replaces the one above as the layers are lost from the surface.
Which virus can induce hyperproliferation of epithelial cells and how?
Papilloma virus
They do this by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation
Which results in a surface growth
what forms if the increase in cell production is greater than cell loss from the surface of the eidermis?
cells accumulate and produce “hard skin” or a corn
How does increased cell proliferation lead to tumour formation?
When there is too much cell proliferation, the rate of cell loss is not sufficient to maintain the normal tissue volume and too much tissue is formed
This is a benign tumour called an adenoma
Although not malignant, these adenomas have a high risk of acquiring more mutations that switch it to becoming cancerous
What does hyper-proliferation result in?
increased cell numbers and a thickening of cell layers e.g., in response to repeated or constant pressure
If the increase in cell production is greater than the cell loss from the surface, cells will accumulate creating an increased thick hard layer
Cell turnover summary…
cell loss= cell production= steady state
cell loss> cell production= reduction in tissue mass
cell loss< cell production= increased tissue mass
What can result to changes in the steady state?
normal physiological responses or pathological responses
What is a main example of a normal physiological response causing a change in steady state?
female reproductive biology
cyclic production and loss of the endometrial epithelial lining of the uterus in the menstrual cycle
the large increase during pregnancy, in the number and size of epithelial glands of the breast, and their loss after weaning (stopped breastfeeding)
