Session 4 - Epithelial Tissue Flashcards
Define a tissue
A collection of cells that are adapted to perform a specific function
Define an organ
The state where two or more tissues are combined to create a structural unit that has a particular function that are a sum of its parts.
What are the 4 broad tissue categories?
Epithelial tissue
Connective tissue
Muscle tissue
Nerve tissue
List how epithelial cells adhere to one another at the cells lateral surface.
Tight junctions Adherence junctions Desmosome Gap junctions Cell adhesion molecules: integrin, selectin, CAM
List how epithelial cells adhere to one another at their basal surface.
Hemi-desmosome Focal adhesions Integrity Proteoglycans Cell adhesion molecules
What enables paracellular transport and where does it occur?
In the gut, tight junctions can open transiently to allow small molecules to cross such as sugars, amino acids etc.
Where are adhesion junctions exclusively found and what are they?
They are only found in epithelial and endothelial cells and are always 1/3 the distance from the luminal surface. They are made from E-cadherin proteins which are attached to the Intracellular actin filament network. Found as a belt and act to stabilise the tissue and act as another barrier
How are desmosomes constructed and where are they found?
They are the strongest cell adhesion molecule and as such are found in tissues that experience allot of mechanical stress such as cardiac tissue and the skin (the are the only cell adhesion molecule in the skin). They are found ~ 1/2 way between cell lateral surface and have a random distribution. E-Cadherin proteins being across cells and they are found to the cytokeratin network Intracellularly
Describe the function of gap junctions and where they are located. And what are they made up of?
Close to the base of epithelial cells. They allow for quickly communicating signals between cells as they allow for the free movement of small molecules.
Thus is particularly important in smooth and cardiac tissue to signal contraction of neighbouring cells.
They are made up of a hexagonal arrangement of connexins.
What are the only cells that don’t have gap junctions?
Motile cells that are in contact with each other such as spermatozoa and erythrocytes
Why does the myometrium in the uterus change from Connexin 45 to Connexin 35 in preparation for birth?
Connexin 35 form wider gap junctions when they coalesce and as such they allow the transport of Ca2+ ready for contraction
Where are hemi-desmosomes found and how do they adhere?
They are found on the basal surface of epithelial cells and attach to the collagen fibres found in the extracellular matrix of the connective tissue (not the basal membrane) through integrins which are bound onto the the network of intermediate fibres within the cell (same cytokeratin fibres of desmosomes)
What is the difference between hemi-desmosomes and focal adhesions?
Both connect to connective tissue collagen and via integrins but are attached to Intracellular actin filaments.
What is required for all of the adhesion molecules to work?
Calcium ions.
Define a mucosal membrane and give some examples
The structure that lines all the “moist” hollow internal organs of the body.
It’s continuous with the respiratory skin at various body openings
GI, urinary, respiratory tract
Name the layer of the GI tract in order
Mucosa (Epithelium, Lamina Propria, Muscularis Mucosa)
Sub mucosa - connective tissue layer containing arteries, nerves and veins.
Muscularis external (inner circular, outer longitudinal)
Serosa
What kind of epithelial cells line the corpuscles (glomerulus) and what line the collecting ducts of renal system?
Squamous epithelium - corpuscle
Cuboidal epithelium - collecting duct
In the urinary tract what order do the layers of muscle in the Muscularis external appear?
Longitudinal muscle is first and then circular muscle follows. This is the opposite to the GI tract
What type of epithelial cell is found in the urether and what is the name it is known by?
Transitional, urothelium
Name some features that protect the bladder from damage.
Mucosa secretes mucus which protects against acidic conditions.
Many tight junctions stop any toxic molecules leaving bladder.
What are the 2 parts of the respiratory tract?
Conducting portion - nasal cavity to the bronchi
Respiratory portion - bronchi to the alveoli
Describe the structure of the trachea and the primary bronchi
-Pseudostratified ciliated columnar epithelium
-Sub-muscosa contains glands that secrete watery mucus (mucin and water-make sticky mucus, serum proteins - lubricate the surfaces, lysozyme- destroy bacteria, anti-protease - inactivate bacterial enzymes)
C-shaped hyaline cartilage ring
Describe the structure of the secondary and tertiary bronchi.
Same as trachea bar cartridge is crescent moon shaped not c shaped.
Trachea:
-Pseudostratified ciliated columnar epithelium
-Sub-muscosa contains glands that secrete watery mucus (mucin and water-make sticky mucus, serum proteins - lubricate the surfaces, lysozyme- destroy bacteria, anti-protease - inactivate bacterial enzymes)
C-shaped hyaline cartilage ring
Describe the structure of the alveolus.
Squamous epithelium to basal lamina and the endothelium.
Folds in basal lamina allow for expansion.
Name the 3 closed cavities and what kind of epithelial cell lines them?
Peritoneal - covers organs in the abdomen
Pleural - between the lungs
Pericardial - surrounds the heart
These are types of mesothelium
Name the 8 different types of epithelial cells structure
Simple/stratified squamous Simple/stratified cuboidal Simple/stratified columnar Pseudostratified columnar Transitional
Give some examples of where simple squamous cells are found.
Lining of heart, blood vessels, mesothelium (pleural, peritoneal cavities)
Give some examples of where simple cuboidal cells are found
Ducts of exocrine glands, kidney tubules
Give some examples of where simple columnar cells can be found.
Lining of GI tract and excretory ducts of glands.
Give some examples of where pseudostratified columnar cells are found.
Upper respiratory tract,
Give some examples of where stratified squamous cells can be found
Epidermis, mouth, oesophagus, vagina
Give some examples of where stratified cuboidal cells be found
Ducts of sweat glands
Give some examples of where stratified columnar cells can be found
Conjunctiva of the eye and some secretory portions of the male urethra
Give some examples of where transitional epithelial cells.
Lining of the bladder
Define epithelial
Sheets of contiguous cells , of varied origin, that cover the external surface of the body and line many internal surfaces.
Name 6 surface specialisations of epithelial cells.
Keratin - prevents water loss
Cilia - control micro movement of luminal content
Goblet cells - mucus secretions, moistens ad lubricates
Club cells - act as stem cells for respiratory epithelium
Micro fold cells - rapid sampling of gut micro flora
Stereocilia - auidtory system
Where is the mutation that causes cystic fibrosis and what does it cause?
Mutation is in the CFTR gene (cystic fibrosis transmembrane conductance regulator). This results in a deficiency of chloride ion release into the mucus so less water follows making the mucus very viscous and as such it isn’t cleared leading to raised infection risk. Affects anywhere musus is secreted: pancreas, respiratory tract, GI tract, reproductive tract, liver (bile duct), skin
Define metaplasia and neoplasia
Metaplasia- capacity to change from one type of epithelium to another .
Neoplasia - changes that give rise to a tumour (a carcinoma).
What is the name given to tumour cells of an epithelial cell origin?
Adenocarcinoma
From chronic smoking why is there permanent damage to the lungs?
Club cells are damaged. These are a type of stem cell so are not replaced hence why the damage is permanent.
What are the early effects of smoking on the lungs.
1 - normal mucus layer thickens
2 - cilia die off
3 - ciliagenesis - 2-4 days will restart (if stop smoking and the mucus layer is cleared)
What are the chronic affects of smoking on the lungs?
1 - goblet cells and basal cells proliferate
2- club cells metaplasia or die
3 - carcinogens induce mutations and malignancy
4 - pneumocytes in the alveoli die
5- fibroblasts lay down scar tissue which is hard to repopulate over
