Apical epithelial surface

Cilia are thin cylindrical hair-like structures with a cross-sectional radius of 0.1 gm projecting from the apical epithelial surface of ciliated columnar cells. Ciliary length is thought to correspond to periciliary fluid depth and range from approximately 7 gm in proximal airways to roughly 5 gm in more distal airways.- Each ciliated epithelial cell supports approximately 200 cilia at a density of eight cilia/gm. Short microvilli, possibly associated with secretory functions, are interspersed among the cilia. 

Apical epithelial surface In the airway, surface interfacing with lumen. 

However, in interphase delaminating neuroblasts, which are known to have completed S-phase and are at the G2 stage of the cell cycle, this codependence of Baz/Insc/Pins seen in mitotic neuroblasts does not apply. Delaminating neuroblasts possess an apical membrane stalk which retains contact with the epithelial surface and this is where apical cortical localization of Insc is initially seen (see Fig. 2). This initial localization of Insc to the apical stalk occurs... 

A deep layer rich in mucus and the origin of which is to be found in the conjunctival calyciform cells. This mucus is in relation with the apical epithelial cells via the glycocalyx. This interface between the lacrymal secretion and the epithelium influences the quality of the corneal surface. Indeed, the stability of the lacrymal secretion and the epithelial absorption of its metabolites both depend on the mucin and the apical expansions of the epithelial cells [2]. 

Implantation and subsequent placentation is a unique mammalian form of reproduction. A fertilized mammalian egg autonomously develops into a blastocyst, which must be successfully implanted in the uterus to develop further into a fetus. Initial adhesion of the embryo to the uterus occurs via the apical cell membrane of two polarized epithelial cells, the trophoblast of blastocysts, and surface epithehal cells of the endometrium. This adhesion is unique because it is apical-apical adhesion between two epithelial cells, whereas generally apical cell surfaces of epithelia are nonadhesive. 

A number of recent reports have identified KS associated with epithelial surfaces. In adult tissues, keratinocytes, uterine endometrial cells, corneal endothelium, sebaceous gland, salivary gland, and sweat gland epithelia exhibit KS immunoreactivity [30-32]. Additionally KS is expressed by epithelial-derived carcinoma cells [33, 34]. Recently the endometrial protein MUCl was shown to bear KS chains [35]. This glycoprotein is a common component of the mucin layer associated with apical surfaces of secretory epithelia and could be responsible for the KS observed in many of these glandular surfaces. Another cell-surface molecule CD44 has been... 

Figure 1 Micrograph of a rat tracheal explant The explant was initially exposed to amosite asbestos for 1 hr, then maintained in air organ eulture for 7 days, and fixed and processed for histological assessment. Note the adherent mass of fibers on the apieal epithelial surface some fibers have been taken up by the epithelium and some (arrows) have been translocated to the connective tissue layer beneath the epithelium. Cartilage is visible at the bottom of the field. Space between mass of fibers and apical surface is an artifact of cutting direction. (From Ref 161.)...

Airway cross-sections have the nominal anatomy shown in Fig. 5.16. Airway surface liquid (AST), primarily composed of mucus gel and water, surrounds the airway lumen with a thickness thought to vary from 5 to 10 mm. AST lies on the apical surface of airway epithelial cells (mostly columnar ciliated epithelium). This layer of cells, roughly two to three cells thick in proximal airways and eventually thinning to a single cell thickness in distal airways, rests along a basement membrane on its basal surface. Connective tissue (collagen fibers, basement membranes, elastin, and water) lies between the basement membrane and airway smooth muscle. Edema occurs when the volume of water within the connective tissue increases considerably. Interspersed within the smooth muscle are respiratory supply vessels (capillaries, arteriovenous anastomoses), nerves, and lymphatic vessels. 

Figure 6, Polarized epithelial cells in culture. Epithelial cells in culture possess an apical surface with microvilli that faces the tissue culture medium (equivalent to the lumenal side of the cells in vivo), and a basolateral surface that faces the tissue culture dish (equivalent to the blood side of the cells in vivo).

Fig. 9 Schematic representation depicting the movement of molecules from the absorbing (mucosal or apical) surface of the GIT to the basolateral membrane and from there to blood. (A) transcellular movement through the epithelial cell. (B) Paracellular transport via movement between epithelial cells. (Q Specialized carrier-mediated transport into the epithelial cell. (D) Carrier-mediated efflux transport of drug out of the epithelial cell. (Copyright 2000 Saguaro Technical Press, Inc., used with permission.)...

The apical surface is loaded with more than 20 different digestive enzymes and proteins the protein lipid ratio is high 1.7 1 [63]. The half-life of these proteins is 6-12 h, whereas the epithelial cells last 2-3 days. So the cell must replace these constituents without depolarizing itself. The cytoskeleton may play a role... 

Figure 2.7 Schematic of the apical phospholipid hilayer surface of the epithelial cells, indicating three types of passive diffusion transcellular (la > 1 b 1 c), paracellular (2a >2b 2c), and the hypothesized lateral, under the skin of the tight junction (3a—> 3b—> 3c) modes. Tight-junction matrix of proteins highly stylized, based on Ref. 75. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

Said et al. [78] directly measured the acid microclimate on the surface of gastrointestinal tract (GIT) epithelial cells (intact with mucus layer) in rats. The pH on the apical (donor) side of the cells varied from 6.0 to 8.0, while the pH on the basolateral (acceptor) side was 7.4. Furthermore, the pH gradient between... 

P-glycoprotein is not only expressed in tumor cells, but also in cells of several healthy tissues. In liver it was detected in the biliary canalicular surface of hepato-cytes and the apical surface of small biliary ductules. In the small intestine and colon, it is localized in the apical surface of columnar epithelial cells, and in kidneys it is found in the brush border membrane of proximal tubules. Moreover, it is detectable on the apical surface of small ductules in the pancreas and on the surface of cells in the medulla and cortex of adrenals [2]. 

The number of channels synthesized, processed, and trafficked to the apical membrane and rate of CFTR internalization at the apical membrane determine the cell surface density. Mutations in CFTR that alter one or more of these parameters decrease total CFTR-mediated anion flux and impair epithelial cell function. 

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