levels of organization...2012/02/01 · 1. tight junctions or zonulae occludens forms a band...
TRANSCRIPT
How do individual cells “connect” to form tissue?
Levels of Organization
http://animalcellbiology.wordpress.com/category/structure/
Desmosome
Tight Junction
1. Tight Junctions or Zonulae Occludens
forms a band completely around the cell
fusing cells together
and closing-off intercellular space.
Fusion site #: often correlates to leakiness of tissue.
The fewer fusion sites the more permeable to
water and solutes
More fusion sites less permeable…
Ex: Cells of the proximal renal tubule of the kidney where
filtration often takes place have few fusion sites to allow for
leakability, whereas, cells of the urinary bladder (that must hold
urine and not allow it to leak out) contains numerous fusion sites
or tight junctions to form a seal to prevent the flow of materials
between epithelial cells.
2. Gap junction (communicating junction)
a gap between the neighboring cell membranes
contains protein unit called connexin surrounds the pore,
which acts as a hydrophilic ion channel between two cells.
An individual unit of the gap junction is called a connexon .
3. Desmosome (anchoring junctions)does not surround the cell. It’s adhesion function is further
empowered by groups of intermediate keratin filaments which
provides firm adhesion.
Hemidesmosome literally means half a desmosome
Plant Cell Wall
From a functional point of view, junctions between cells can be classified as:
adhering junctions (desmosome and hemidesmosome), impermeable junctions (tight junctions) and communicating junctions(gap junctions).