Epeithelial cell junctions

[ctizzle13498]

Does anyone have a simplified version to describe these zona occludens, zona adherens, macula adherens.

I keep getting confused what they actually do

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[norealname]

I am assuming you are asking this question because of the NBME 11 or NBME 12 question on the same topic.

I would know some basic concepts about the occluding junctions and desmosomes especially. I don't know of any specific function of the adhering junctions.

Occluding junctions are the junctions closest to the apical surface of epithelial cells, they are important in forming blood barriers (blood-brain barrier, blood-air barrier, etc). They also prevent backflow of substances across epithelial surfaces (for example in the kidney tubules or GI tract)

Desmosomes are located further away from the apical surface of cells and are more important in holding epithelial surfaces together, especially in those surfaces under constant mechanical stress (skin, esophageal lining, etc...).

 

[gravitywave]

zona adherens: actin-cadherin-actin connections, says "I am here" to the neighboring cells.

 

[SOML]

Zonula Occludens
aka "Tight junction"
selective permeable barrier bet. apical/basolateral PM's

Zonula Adherens
cross links by myosin, a actinin, vinculin
stabilizes epithelium by connecting terminal webs of adjoining cells
cell-cell adherence

Macula Adherens
Desmosomes (links cytoskeletons of adjoining cells - LATERAL)

Gap Junctions "Nexus"
Hemidesmosomes (anchor basal cell to basal lamina - BOTTOM)
2 defined layers:
lamina lucida - transparent. adjacent the epith. large proteoglycan. Type IV
lamina densa - meshwork of Type VII. anchoring typeVII loops aroung Type I

 

[boomboompowpow]

sorry SOML - but your wrong about the gap junctions

gap junctions = nexus
2 x 6 connexin half-channels of two adjacent cells join together
--> barrier-free exchange of ions/molecules up to the size of cAMP possible

hemidesmosomes:
intermediate filaments (e.g. cytokeratines) of the basal cell are chained to integrins and further to anchor filaments of the basal lamina
--> if not intact --> bullous pemphigoid

 

[SOML]

sorry SOML - but your wrong about the gap junctions

gap junctions = nexus
2 x 6 connexin half-channels of two adjacent cells join together
--> barrier-free exchange of ions/molecules up to the size of cAMP possible

hemidesmosomes:
intermediate filaments (e.g. cytokeratines) of the basal cell are chained to integrins and further to anchor filaments of the basal lamina
--> if not intact --> bullous pemphigoid

Yes, membranes on each side contains circular patches called connexons, Hemisdesmosomes is different, it's for anchoring basal cells to basal lamina.. mybad = P