10: Cell interactions & junctions

Question 1

What are the roles of tight junctions?

Answer 1

To hold cells together; prevent passage of molecules between cells
Materials must enter cells to cross the tissue
Control what is passed through
e.g. blood-brain barrier

Block movement of membrane proteins between regions of cell, allowing specialised functions

Question 1

What are the 3 types of cell junctions?

Answer 1

1. occluding or tight junctions : seal epithelial cells together tightly to prevent even small molecules from leaking from one side to the other
2. anchoring junctions: mechanically attach cells to their neighbours or to the extracellular matrix (by linking cytoskeleton of neighbouring cells or anchoring cells to extracellular matrix)
3. communicating junctions: mediate the passage of small molecules from one cell to the next (by connecting cytoplasm of neighbouring cells)

Question 2

How is epithelia classified depending on the numbers of tight junctions?

Answer 2

Tight epithelia : blood brain barrier; gut epithelium
Leaky epithelium : kidney tubules