Epithelial tissue Flashcards
Function of epithelial tissues
- Covers body surfaces
- lines hollow organs
- forms the glands of the body
What are cell junctions
Cell junctions are connection points between the plasma membranes of adjacent cells.
There are namely 5 types: gap junction, adherens junction, desmosomes, hemidesmosomes, and tight junction.
Key functions of epithelial tissues
A group of similar cells that work together to cover body surfaces and line hollow organs, body cavities, and ducts; it also forms glands.
- selective barriers (limit or aid transfer)
- secretory (onto a free surface)
- protective (especially from abrasion)
What do each arrow point to
- Tight junction
- adherens junction
- Gap junction
- Desmosome
- Hemidesmosome
What is the apical surface
The edge surface of epithelial tissue facing the body surface, body cavity, lumen of an internal organ, or a tubular duct that receives cell secretions. They may contain cilia or microvilli
What is the lateral surface
The surface of an epithelial cells which face the adjacent cells on either side - these surfaces contain junctions (gap, desomosome, tight, adherens)
What is the basal surface
The deepest layer of epithelial cells facing the basement membrane - these may contain hemidesmosome junctions.
Cytoskeleton - Microfilaments
- bundles beneath cell membrane and cytoplasm; strength; alter shape; link cytoplasm to membrane; tie cells together; muscle contraction e.g actin
Cytoskeleton - Intermediate filaments
- strength; move materials through cytoplasm e.g keratin
How are epithelial cells arranged
Arranged into flat, continuous sheets and can be comprised of single or multiple layers
What is actin
A type of microfilament - protein bundles beneath cell membrane and cytoplasm that determine cell shape and structure and allow for muscle contraction
What is keratin
A type of intermediate filament - structural roles in the cytoplasm of cells, also allow movement of material within cytoplasm
Structure of tight junctions
Located near the apical surface
Strands of transmembrane proteins (claudins and occludins) link adjacent plasma membranes in a ‘sewing-like’ appearance
No gap is left
Function of tight junctions
Joins adjacent plasma membranes tightly together keeping cell polarity (ie electrically tight) by preventing migration of proteins between apical and basal surfaces
What cell junction is this
Tight junction
Where are tight junctions located
Stomach, intestines, and bladder
What are claudins and occludins?
Transmembrane proteins that form the tight junction
Structure of adherins junction
Located near the apical surface
Two plaques (patches of protein tissue) on each membrane linked together by transmembrane glycoproteins (cadherin) - belt-like appearance
What do the cadherins do in the adherens junction
Span the gap but links cell surface to Keratin
What do the catherins do in the adherens junction
Link the cadherins to Actin
Adherens junction prevents __ ____ from tensions forces like in contractions
Cell separation
What cell junction is this
Adherens junction
Structure of the desmosome junctions
A lateral wall and has plaques
What is the similarity between adherens and desmosome junctions
Both have plaques
What is the funciton of the desmosome junction
Resist shearing forces
What cell junction is this
Desmosome
What does keratin do in desmosome junction
Spans from one desmosome to another on other side of the cell - structural integrity
Where are desomosome junctions most commonly found
Skin epithelium and cardiac cells of the heart to prevent pulling apart
What is the structure of the gap junction
6 connexin protein molecules form a connexon or hemichannel.
2 hemichannels make up a gap junction
What is the function of the gap junction
Opens up a tunnel from one cell to another, and sends messages (irons, RNA etc.) and allows cell tissue communication. Also coordinated movement
What cell junction is this
Gap junction
How can gap junctions communicate
Open up a tunnel from one cell to another, send messages (ions, RNA etc)
What is the function of the hemidesmosome
- Connects epithelia to basement membrane.
- Links cellular basal intermediate filamentt (keratin) to basement membrane