1. A channel between two adjacent cells in known as an intercellular cleft.
2. And through these channels many molecules can easily pass between cells.
3. Importance of Intercellular clefts:
i) It is very important in transportation of fluids and small solutes.
ii) It contains gap junctions, tight junctions, desmosomes, and adheren proteins and these junctions help in regulate cell communication by signal transduction, surface receptors, or a chemogradient.
Capillaries are small exchange vessels (6-10 μ) composed of highly attenuated (very thin) endothelial cells surrounded by basement membrane − no smooth muscle
There are three structural classifications:
Continuous (found in muscle, skin, lung, central nervous system) − basement membrane is continuous and intercellular clefts (between adjacent endothelial cells) are tight (i.e., have tight junctions); these capillaries have the lowest permeability
Fenestrated (found in exocrine glands, renal glomeruli, intestinal mucosa) − perforations (fenestrae) in endothelium result in relatively high permeability
Discontinuous (found in liver, spleen, bone marrow) − large intercellular gaps and gaps in basement membrane result in extremely high permeability
Large surface area and relatively high permeability (especially at intercellular clefts) to fluid and macromolecules make capillaries the primary site of exchange for fluid, electrolytes, gases, and macromolecules
