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
