Respiratory epithelium basal cells

The highly vascularized respiratory epithelium is composed of five major cell types ciliated cells, nonciliated cells, columnar cells, goblet cells, and basal cells. Low numbers of neurosecretory cells are present in the basement membrane [17]. Approximately 20% of the total number of cells in the lower turbinate area is ciliated with fine projections ( 100 per cell) on the apical cell surface. Cilia are used to transport the mucus toward the nasopharynx. These long (4-6 fxm) and thin projections are mobile and beat with a frequency of 1,000 strokes per min. Ciliated and nonciliated columnar cells are populated with about 300 microvilli per cell, which help in enlarging the surface area. 

To determine doses to be used in chronic inhalation studies, F344 rats and B6C3Fi mice of both sexes were exposed to 0, 3, 15, or 75 ppm 1,2-dibromoethane for 13 weeks (NTP 1982 Reznik et al. 1980). Lesions occurred in respiratory turbinates in the dorsal portion of the nasal cavity of rats and mice exposed to 75 ppm. Respiratory epithelium was affected with cytomegaly of basal cells, focal hyperplasia, loss of cilia, and squamous metaplasia. Rats exposed to 15 ppm... 

After acute mild insult the nonciliated cells proliferate and the epithelium regenerates to normal. In the airways, nonciliated basal cells are the main proliferating population. In the bronchioles, the Clara cell is the main precursor cell for regeneration. Because of the delicate nature of the respiratory tract epithelium and the close proximity of subepithelial blood vessels, an inflammatory response occurs to all but the mildest form of injury. Many lesions are therefore diagnosed as rhinitis, tracheitis, and bronchiolitis and qualified as acute, subacute, and chronic depending on the stage of the response. 

A -Vinyl-2-pyrrolidone metabolites and polyvinyl pyrrolidone are excreted mainly in urine. Inhalation of low concentrations of A -vinyl-2-pyrrolidone by rats can cause nasal cavity inflammation, atrophy of olfactory epithelium and hyperplasia of the basal cells of the respiratory and olfactory epithelium. In humans and experimental animals, polyvinyl pyrrolidone accumulates in vacuoles of cells of many organs and, in humans, may be accompanied by pulmonary fibrosis and pneumonia. There have been no genetic toxicity studies with either compound. 

Figure 9.2 Diagram of the four cell types in the nasal respiratory epithelium. A ciliated columnar cell covered by cilia and microvilli of uniform length B basal cell C goblet cell packed with mucus granules D nonciliated columnar cell, covered by microvilli of uniform length. (Redrawn from Mygind, N., 1979 Nasal Allergy, 2nd edition. Blackwell Scientific Publications Oxford).

A layer of epithelium covers the interior of the airway tract. This epithehum contains various cell types such as ciliated, goblet, brush, and basal cells [34]. All cells are in contact with the basement membrane however, basal cells do not reach the airway lumen. Moving through the smaller bronchi and bronchioles toward the respiratory portion, the histological organization of both the epithelium and the underlying lamina propria gradually becomes more simple. 

The superficial layer is used to classify the stratification into simple, which consists of a single layer of cells, and stratified, which consists of more than one layer of cells. Stratified epithelium is usually composed of three layers. Cell division takes place in the basal cell layer (layer 1). Cells migrate and differentiate in the intermediate cell layer (layer 2) until they reach the superficial cell layer (layer 3). Specializations include keratinized and ciliated cells. Keratinized epithelium, which contains the cytoskeletal protein keratin and provides a tough impermeable barrier, occurs mainly in the skin. Ciliated cells have apical plasma membrane extensions composed of microtubules capable of beating rhythmically to move mucus or other substances through a duct. Cfiia are common in the respiratory system. 

Figure 1 Schematic representation of the respiratory epithelium showing ciliated type II cells (EC), dendritic cells (DC), goblet cells (GC), submucosal lymphocytes (LYM), mast cells (MC), alveolar macrophages (AM), and basal lamina (BL). Exposure to particles causes epithelial cells and macrophages to release a variety of immunoreactive mediators.

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. 

The relatively large size of the tubular cells renders electrometric analysis simpler. The basal infoldings of the proximal tubular epithelium of Necturus do not obliterate the intracellular space as they do in this segment of the mammalian nephron. The absence of respiratory and pulsatile movements permits more stable cellular impalements. 

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