Tight junctions

Structure: Region where outer leaflets of adjacent plasma membranes fuse to form a zone around entire apical perimeter of cells (stitching)

Function: Prevents entrance/exit of substances into intercellular space from lumen

Intermediate Junction

Structure: extends completely around perimeter of epithelial cells, basal to ZO. Reinforced by a mat of actin filaments that extend into the terminal web

Desmosome

Structure: Focal diskshaped adhesive junction between adjacent epithelial cells (intermittent spot weld). A dense plaque is pesent on cytoplasmic sufance of each opposing plasma membrane. Tonofilaments loop into and out of plaques on cytoplasmic side.

Function: Prevents from losing wanter and keeps cells together

Not limited to epith.

Structure: separated subunits arranged radially around a central channel

Function: Allows passage of ions and small molecules from cell to cell - means of transmitting an impulse from one cell to another

Structure: fingerlike or irregular projections that interlock adjacent epithelial cells

Function: keeps cells together. Excessive interdigitation means that the cell is for absorbing water from lumen (gallbladder, colon, etc)

Unicellular (GI and resp. epithelia)

Multicellular

1. Num cells (multi cell - simple/cmpd gland) 
2. Type of duct (lobes, lobules) 
3. Shape of glandular unit (acinar/alveolar, tubule) 
4. Type and mode of secretion (mucous, serous, mixed; merocrine, apocrine, holocrine)