Junctional complexes

Although a portion of the nutrients released from feedstuff s is absorbed by diffusing across the apical membrane of enterocytes or through the junctional complexes of adjacent enterocytes (paracellular absorption), the majority of nutrients are absorbed from the lumen of the GIT by carrier proteins that are inserted into the apical membrane of enterocytes and colonocytes. 

Figure 2 (Left) Microscopic magnification (X46,500) of mucosal surface (S) associated with intestinal microvilli (V). (Right) Schematic of the microvilli illustrating the cytoskele-ton elements including junctional complexes. (From Ref. 76.)... 

Figure 9 Magnification (X52,700) and schematic of tight junctional complex and lateral intercellular space. (From Ref. 74.)...

In addition, the physical dimensions of the cells making up the monolayer should be considered. Cell shape can influence the relative contributions of the paracellular and transcellular pathways. For example, junctional density is greater in cells that are narrow or of small diameter than in cells that are wide or spread out on the substrate. The height of the cells can impact the path length traveled by a permeant, as will the morphology of the junctional complex and lateral space (Section m.B.2). It is unknown how the mass of lipid or membrane within a cell influences transcellular flux of a lipophilic permeant. 

The tight junction is a component of the junctional complexes which join cells. Immediately basolateral to the tight junction is the zonula adherens (Figs. 6 and 7). Because the zonula adherens and the gap junctions are focal contact regions, they do not impact transport by the paracellular pathway. All of these junctions are specialized regions of the lateral cell membrane which demarcate the lateral space. In certain types of cells the lateral space is rather narrow and... 

Lutz KL, T Siahaan. (1997). Molecular structure of the apical junction complex and its contribution to the paracellular barrier. J Pharm Sci 86 977-984. 

B Gumbiner, K Simons. (1987). The role of uvomorulin in the formation of epithehal occluding junctions. In Anonymous. Junctional Complexes of Epithehal Cells, CIBA Foundation Symposium 125, New York Wiley, pp 168-186. 

The synapse is a specialized junctional complex by which axons and dendrites emerging from different... 

The biochemical properties of these structures are known. Desmosomes display protease sensitivity, divalent cation dependency and osmotic insensitivity and their membranes are mainly of the smooth type. In direct contrast to desmosomes, the tight junctions as well as gap junctions and synapses display no protease sensitivity, divalent cation dependency or osmotic sensitivity, while their membranes are complex. These facts have been used in the development of techniques to isolate purified preparations of junctional complexes. 

In tissue culture, astrocytes, hippocampal neurons and arterial myocytes all express al diffusely in their plas-malemma. In contrast, immunocytochemically stained a2 in astroglia and a3 in myocytes and neurons display reticular patterns and colocalize with the Na+/Ca2+ exchanger (NCX) (Fig. 5-6). These plasmalemma reticular patterns coincide with the patterns of staining for junctional complexes on sarcoplasmic reticulum and, in astroglia and neurons, junctional complexes on endoplasmic reticulum [23]. 

Fannon, A M. and Colman, D. R. A model for central synaptic junctional complex formation based on the differential adhesive specificities of the cadherins. Neuron 17 423 34,1996. 

Yoshida Y, Okano M, Wang S, Kobayashi M, Kawasumi M, Hagiwara H, Mitsumata M (1995). Hemodynamic-force-induced difference of interendothelial junctional complexes. Ann. N Y. Acad. Sci. 748 104-120. 

The columnar, cuboidal basal cells are 18-20 xm in height and 8-10 iim in diameter. They form a monolayer adhered to a basement membrane by hemidesmosomes which are linked to anchoring fibrils of collagen type VII. At the lateral borders, basal cells are extensively interdigitated and joined together in places only by junctional complexes (zonula adherens), desmosomes, and gap junctions. 

In the past, changes in RTj were viewed in terms of assembly/disassembly of the tight junctional complex (reviewed in 93). Recent studies in human vaginal-cervical epithelia have shown acute and reversible modulation of Rtj that are the result of conformational changes in assembled tight junctions [13], The examples presented below relate to effects of modulation of extracellular calcium level (Ca0) and treatments with ATR... 

Gorodeski GI and Goldfarb J [1998] Seminal fluid factor increases the resistance of the tight junctional complex of the cultured human cervical epithelium CaSki. Fertil Steril 69 309-317... 

Their cytoplasmic membrane is bristled up with microvillosities and micropilis. They increase the exchange surface with the lacrymal secretion and enable its fixing. Their lateral and basal cytoplasmic membranes have got junctional complexes uniting these superficial cells together. There are three types of junctional complexes ... 

These junctional complexes all disappear during desquamation. 

Fig. 6. Ion-Concentrating Systems. The microvilli at calciferous mucosal gland cells of the earthworm resorb ions from the lumen which are moved into the intercellular spaces behind the junctional complex (Jc) followed by an isotonic secretion into the blood.

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