Columnar mucosal cells

The columnar epithelial cells of the intestinal mucosa actively absorb and secrete extracellular ions, nutrients, and water. The active secretion of ions by these cells with an accompanying fluid flux acts to dilute and purge microorganisms or toxins in the bowel promotes the transfer of secretory immunoglobulin A, antimicrobial defensin peptides, and mucin into intestinal mucus and the gut lumen and, by affecting intraluminal pH, may alter the growth characteristics of enteric microflora [121]. Mucosal secretion is modulated by several enteric neurotransmitters, as well as inflammatory mediators released by mucosal mast cells that may affect transport indirectly through their ability to stimulate enteric neurons [122],... 

Q1 The mucosa is a mucous membrane which forms the innermost layer of the intestine. In the small intestine the mucosal surface area is increased greatly by folds and by villi, finger-like projections containing a core with a lymph capillary (lacteal) and blood vessels. Villi are covered by absorptive columnar epithelial cells whose luminal surface is further increased by microvilli (brush border) on which digestive enzymes and transport mechanisms for inorganic ions are located. 

Induction of Calbindin-D In response to crdcitriol administration, there is an increase in mRNA synthesis and then in the synthesis of calbindin-D in intestinal mucosal cells, which is correlated with the later and more sus-teilned increase in calcium absorption. In -vitamin D-deficient animals, there is no detectable calbindin in the intestinal mucosa, whereas in animals adequately provided with vitamin D, it may account for 1 % to 3% of soluble protein in the cytosol of the columnar epithelial cells. Although the rapid response to calcitriol is an increase in the permeability of the brush border membrane to calcium, the induction of calbindin permits intracellulcu accumulation and transport of calcium. The rapid increase in net calcium transport in tissue from -vitamin D-replete animals is presumably dependent on the calbindin that is already present in deficient animals, there cem be no increase in calcium transport until sufficient calbindin has accumulated to permit intracellular accumulation, despite the increased permeability of the brush border. 

The third mucosal layer is that lining the entire length of the small intestine and which represents a continuous sheet of epithelial cells. These epithelial cells (or enterocytes) are columnar in shape, and the luminal cell membrane, upon which the microvilli reside, is called the apical cell membrane. Opposite this membrane is the basal (or basolateral) plasma membrane, which is separated from the lamina propria by a basement membrane. A sketch of this cell is shown in Fig. 5. The primary function of the villi is absorption. 

The pharynx, larynx, trachea and bronchi are lined with pseudostratified, ciliated columnar epithelium that contain at least eight cell types, including mucous secretory goblet and Clara cells, which produce a protective mucus layer of 5-10 jum thickness (see Table 9.2). Subepithelial secretory glands, present in the bronchial submucosa, also contribute to the mucus blanket [9]. Through coordinated ciliary movement a propulsive wave is created, which continuously moves the mucus layer up towards the larynx. Consequently, the mucosal surface of trachea and bronchi is constantly swept to remove inhaled materials. As the bronchi divide into bronchioli, the ciliated columnar respiratory epithelium is much thinner and changes to a simpler non-ciliated cuboidal epithelium. The epithelium in the terminal and respiratory bronchioles consists of ciliated, cuboidal cells and a small number of Clara cells. However, Clara cells become the most predominant type in the most distal part of the respiratory bronchioles [10]. 

The mouth and esophagus are composed of two layers, the mucosa and submucosa (Figure 3.5). The mucosa is lined on its outer surface by a stratified squamous epithelium with layers of polyhedral cells of the intermediate layers and low columnar cells of the basal layer. Below the cellular layer is the lamina propria containing loose connective tissue with blood vessels and small aggregates of lymphocytes. Smooth muscle within the mucosa (muscularis mucosal layer) is seen as small bundles. The submucosa... 

In the cervix, HPV infects epithelial cells that lie under the mucosal membrane (see Figure HPV-4). The types most responsible for cervical cancer, HPV 16 and 18, make proteins that bind to two tumor suppressors, one of which is p53, which we saw in Chapter 24. This allows the endothelial cells to divide abnormally. Cancer occurs for reasons still not well understood when the abnormal endothelial cells contact the columnar cells. 

At the junction of the esophagus and stomach, the mucosa undergoes a transition from the protective stratified squamous epithehum to a tightly packed glandular secretory mucosa that contains columnar cells. The muscularis mucosa, the imderlying submucosa, and the muscularis propria remain continuous between the mucosal junction. 

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