MBC - Epithelial Cells and Tissues Flashcards
How would you define a tissue?
Group of cells whose type, organisation and architecture are integral to ints function
What are tissues made up of?
Cells, ECM and fluid
What are the 5 main cell types?
- Connective tissue cells 2. Contractile tissue 3. Epithelial cells 4. Haematopoietic cells 5. Neural cells
What are connective tissue cells?
Chondrocytes, osteocytes, fibroblasts
What are contractile tissues?
Cardiac, smooth and skeletal muscle
What are haematopoietic cells?
Cells that undergo erythropoiesis/ blood cell formation.
What are neural cells?
Neurones/ glial cells
What are epithelial cells?
Cells that form continuous layers to line surface and separate tissue compartments, among many other functions.
What is the term for a tumour in the epithelia?
Carcinoma
What is the term for a tumour in the mesenchymal (connective tissue/muscle) cells?
Sarcoma
What is the term for a tumour in the haematopoietic cells?
Leukaemia/lymphoma
What is the term for a tumour in the neural cells?
Nueroblastoma/glioma
How does epithelial organisation prevent leaking?
Forms continuous cohesive layers along with cell-by-cell junctions to prevent leaking.
What is a key reason for cell-cell junctions?
Integral to the maintenance and functioning of epithelial layers
What are the categories for epithelia shape?
Squamous Columnar Cuboidal
What are the categories for epithelia layering?
Simple Stratified
What are the main categories of these combinations layering/cell shape?
Simple squamous Simple columnar Simple cuboidal Stratified squamous
What other categories of epithelia do we see that are not included in layering/shape combinations?
Pseudo stratified Transitional
What does pseudo stratified mean?
Appears to be more than one layer (stratified) however is in fact simple as all cells have contact with basement membrane.
What are the two sub categories of stratified squamous?
Keratinising and non keratinising
What epithelia tissue would we find in the alveoli?
Simple squamous
What epithelia tissue would we find in the ducts e.g. kidney collecting duct?
Simple cuboidal
What epithelia tissue would we find in the surfaces involved in absorption/secretion e.g. enterocytes?
Simple columnar
What epithelia tissue would we find in the epidermis/lining of mouth anus cervix and vagina?
Stratified squamous
What epithelia tissue would we find in the upper airways and urinary/reproductive tracts?
Pseudo stratified
What is keratinising and why do some squamous cells keratinise?
keratinising is the production of keratin, causing the cell to die and lose its nuclei/organelles. By doing this, cells become thick and protect underlying tissues from chemical/physical insults.
Where would you find keratinising stratified squamous?
Epidermis of the skin - keratinised tissue provides protection
Where would you find non keratinising stratified squamous?
Lining of them mouth, anus, cervix and vagina.
What epithelial cells does pseudo stratified layering usually associate with?
Columnar cells.
What is the need for epithelial polarity?
Polarity gives directionality, which is a key for epithelial secretion, absorption and transport of fluids/solutes
What are the two discrete domains of an epithelial cell?
Apical domain - faces the lumenal surface Basolateral domain - in contact with the ECM and faces the basement membrane (if basal membrane)
What is the lateral membrane?
The membrane on each side of the epithelial cell, facing the ECM.
What happens if there’s no polarity in terms of pumps and channels?
There is no directionality therefore no net flow of ions or solutes as pumps will be found on all sides of the cell.
What happens if there’s no polarity in terms of secretion?
There is no directionality, therefore secretory mechanisms would be found on all aspects of the cell. Normally secretion either occurs into the lumen from apical aspect, or from basal into interstitial space. However secretion without polarity would occur in all directions
What are the types of cell junction?
Gap junctions Tight junctions Desmosomes Adherens
What are tight junctions?
Form a belt around the apical lateral aspect of the cell to seal the gap between cells
What are adherens junctions?
Master junction - controls the formation of all other junctions despite being the least conspicuous on a micrograph
What are desmosomes?
Spot junctions formed between cells that must resist mechanical stress
What are gap junctions?
Channel junctions which allow the movement of materials between cells in order to form communities or sync a number of activities.
What are the 4 main functions of epithelial layers?
Transport Absorption Secretion Protection
Describe the structure of a specialised transport epithelium cell
- Many ion transporters in plasma membrane - High numbers of mitochondria in basal membrane - Basal membrane infoldings - mitochondria focussed on the basolateral domain This is all for active transport which occurs at the basal membrane into nearby capillaries. The apical membrane has channels too however for passive movement into the cell
Where would we find absorptive epithelium?
Enterocytes - brush border of the small intestine (epithelial cells cover the villi)
Describe the structure of an enterocyte
Specialised absorptive epithelial cell: - Brush border (apical side) is covered in plasma projections called microvilli - Apical Brush border contains lots of active transporters and channels for nutrient uptake
How do we get directionality for the flow of nutrients in enterocytes from the gut lumen to the blood capillaries?
Nutrients accumulate in the apical domain of the cell so will naturally diffuse down their concentration gradient to the basal interstitial space to be collected by the capillaries.
In secretory tissues, how is the epithelium usually organised?
Tubules and glands of varying complexity
What are the main types of secretion (macroscopic)?
Endocrine - into the blood stream Exocrine - into glands or ducts
Describe the structure of an exocrine secretory epithelial cell
We have the nucleus and the rER at the basal aspect of the cell, then the Golgi apparatus in the middle and at the top there are many secretory granules in the apical cytoplasm. This is the opposite of the endocrine as it secretes into the lumen nearer to the apical aspect of the cell
Describe the structure of an endocrine secretory cell
We have the nucleus and rER in the apical cytoplasm with the Golgi apparatus is the middle, and the secretory granules in the basal cytoplasm. This is the opposite of the exocrine as it secretes into the capillaries nearer to the basal aspect of the cell.
