Lecture 14: Cells , organs and tissues Flashcards
What are the four major tissue types?
Connective
Epithelial
Nervous
Muscular
What are the characteristics of epithelial muscle and nervous tissue?
Little extracellular matrix
Intermediate filaments and cell-cell junctions for strength
What are the characteristics of connective tisseus?
Lots of extracellular matrix for strength
Few cells
How are epithelia organised?
Cells organised into sheets that can be rolled into tubes
Cover a surface or line a cavity
What are tight junctions?
Forms a seal between cells and stops diffusion across epithelial sheet
What are some characteristics of tight junctions?
In vertebrates
Made of strands of occludin and claudin
Let in lipids but not proteins
Separate apical and basolateral
What is transcytosis?
Polarised transport of proteins from one side of the epithelium to the other
What are the three cytoskeleton linked cell cell junctions in epithelia?
Adherens junction
Desmosome
Hemidesmosome
What do adherens junctions and desmosomes link?
Link cytoskeleton of epithelial cells to their neighbours
Use cadherins
What do hemidesmosomes link?
Link cytoskeleton of epithelial cells to basal lamina
Use integrins
What is the role of cadherins?
Mediate mechanical attachment of epithelial cells to neighbours
What is the cadherin family?
Transmembrane proteins in plasma membrane
Bind to identical cadherin in next cell
Interaction requires calcium
What is an adhesion belt?
Continuous band of adherens junctions
What are adherens junctions made up of?
Cadherins linked to actin filaments
What is the role of cadherin?
To bind to an identical cadherin in the next cells
Specific cadherins determine which cells can interact
What type of cadherin is expressed by epithelial cells?
E cadherin
What type of cadherin is expressed by muscle cells?
N cadherin
What are the roles of cell-cell interactions in preventing cancer?
Specific cadherins let cells recognise each other
Cancer cells don’t express the right cadherin anymore
They might secrete more matrix proteases and digest the basal lamina and escape
What is an example of cancer cells expressing the incorrect type of cadherin?
Expressing N instead of E will make the cells more motile
What are gap junctions?
Membranes are close together
Have connexons that allow transfer of inorganic ions and small water soluble molecules between cells
What are plasmodesmata?
The plant equivalent of gap junctions
Large molecules can pass through
