Ciliated cell

The tracheal epithelium consists of mainly four kinds of cells ciliated cells, goblet cells, brush cells, and basal cells (Rhodin and Dalhamn 1956). In the rat s bronchial epithelium, Jeffery and Reid (1975) recognised eight epithelial cell types and two mesenchymal ones (which are probably migratory). All epithelial cells were attached to the basement membrane, but not all reached the airway lumen  

In the mouse, Taira and Shibasaki (1978) distinguished four types of cells dhated cells, goblet cells, basal cells, and non-dUated cells. Pack et al. (1980) found mouse tracheal epithehum markedly different from that of other species. However, the near absence of goblet cells and the presence of a large number of secretory Clara-like cells make it similar to the distal airways of other species. 

In the trachea of the guinea pig, Dalen (1983) recognised four epithelial cells basal cells, goblet cells, ciliated cells and intermediate cells. 

In the pig, Baskerville (1970b) described ciliated cells, goblet cells, basal cells, and intermediate cells. Brush cells were not seen, although they have been described in bronchioli of the pig (Baskerville 1970a). 

In the sheep, Mariassy and Plopper (1983) observed 6 distinct, granule-containing secretory cells 4 mucous cell categories (M1-M4), serous cells, and nonciliated bronchiolar (Clara) cells. 

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In mammals, ciliated cells line the respiratory air passages, the fallopian tubes, and the ventricles of the brain. The cilia beat in a coordinated manner in waves that propel fluids, suspended cells, and small particles along a surface. The motility of the sperm cell is provided by a single flagellum. 

PI. 2.1B Amphibian AOS, surface of accessory neuroepithelium chemosensory strips divided by non-sensory ridges in lateral nasal sinus of Japanese Red-bellied Newt (iCyaops pyrrhogaster) SEM X 742, R = ridge with microvillous cells and G = groove with ciliated cells and cellular protrusions (from Jones et at., 1994). 

Mucociliary Clearance Mucociliary clearance operates by the coordinated movements of cilia, which sweep mucus out of the lungs towards the pharynx where it is swallowed. There is an inverse relationship between mucus velocity and airway generation, which relates to the lower percentage of ciliated cells, shorter cilia, lower ciliary beat frequency and lower number of secretory cells in the peripheral airways [121]. The reported tracheal mucociliary clearance... 

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. 

Figure 10.1 Typical tracheo-bronchial and bronchiolar epithelia showing the major cell types. The tracheo-bronchial epithelium showing the pseudostratified nature of the columnar epithelium, principally composed of ciliated cells (C), interspersed with goblet cells (G), brush cells (Br), serous cells (S), Kulchitsky s cells (K) and basal cells (B). The bronchiolar epithelium showing the cuboidal nature of the epithelium, principally composed of ciliated cells (C), Clara cells (Cl) and infrequent basal cells. Muc = mucus Ci = cilia N = nucleus Sec = secretory granules.

The sites of action and effects of ozone and other photochemical oxidants are described in Chapters 8 and 9. Recent work with primates has suggested that ozone is absorbed along the entire respiratory tract, penetrates more into the peripheral nonciliated airways, and causes more lesions in the respiratory bronchioles and alveolar ducts as the inhaled ozone concentration increases from 0.2 to 0.8 ppm. The most common and most severe tissue damage was observed in the respiratory bronchioles. The ciliated cells in the terminal bronchioles and the Type 1 cells in the epithelial layer of the proximal alveoli of rats were the... 

Because the mucus layer or the underlying cells may serve as either final accumulation sites of toxic gases or layers through which the gases diffuse en route to the blood, we need simplified models of these layers. Altshuler et al. have developed for these layers the only available model that can be used in a comprehensive system for calculating tissue doses of inhaled irritants. It assumes that the basement membrane of the tracheobronchial region is covered with three discrete layers an inner layer of variable thickness that contains the basal, goblet, and ciliated cells a 7-Mm middle layer composed of waterlike or serous fluid and a 7-Mm outer layer of viscous mucus. Recent work by E. S. Boatman and D. Luchtel (personal communication) in rabbits supports the concept of a continuous fluid layer however, airways smaller than 1 mm in diameter do not show separate mucus and serous-fluid layers. 

The ciliated cells are most vulnerable to damage. The most frequent degenerative changes in these cells are loss of cilia, necrosis, and sloughing of cells into the airway lumen. Necrosis and desquamation of nonciliated and secretory cells are less frequently observed. 

Particles deposited in the nasopharyngeal region are moved to the pharynx by the ciliated cells and mucus and expectorated or swallowed.The clearance rate is relatively rapid with a half-life of 12-24 hours. 

Such changes (decrease of ciliated cells with simultaneous increase of the secretion) are noted for smokers (Gouveia et al., 1982 Mathe et al., 1983) and cause a reduction of the mucociliary clearance. This reduction of the mucociliary clearance, associated with an increased adsorption of the respiratory syncytial virus (RSV) (Donelly, 1996), could also explain the extraordinarily high morbidity and mortality for respiratory infections of children with vitamin A deficiency in developing coimtries (Sommer, 1993). 

However, the lungs are equipped with defense mechanisms especially with regard to the intake of foreign substances from the air. Thus, the upper airways of the respiratory system are lined with ciliated cells, and mucus is secreted, which also lines the airways. Solid particles are therefore trapped by the mucus and cilia and are transported out of the respiratory system. Other substances may be removed after dissolving in the mucus and then being transported out by the ciliary escalator. 

In vitamin A deficiency the internal epithelial surfaces of lungs and other tissues, which are usually rich in mucous secreting cells and in ciliated cells, develop thick layers of keratinizing squamous cells similar to those on the external surface of the body. 

Mucus is cleared continuously by cilia, which extend through the periciliary fluid to hook the mucus layer. The claw-like tips of the cilia engage with the mucus layer and transport the latter toward the nasopharynx [8,9]. Cilia are complex motile structures that extend from the surface of columnar ciliated cells the number of cilia per cell is approximately 200 with a cell density of 6-8 cilia per pm2. These hair-like protrusions range in length between 5 and 10 pm and width from 0.1 to 0.3 pm. 

It is possible to study cilia beat frequency and drug interaction with mucus independently using models such as tissue explants or cultures of ciliated cells or purified mucus preparations. However, these are not able to provide information about mucociliary transport rates. For such studies, a model incorporating the integrated cilia and mucus components is required such as the frog palate. Drugs, preservatives and absorption enhancers, and bioadhesive formulations have been extensively studied in this model [9]. 

For regions where absorptive as well as protective functions are crucial, the epithelia are composed of ciliated cells or microvilli to increase the surface area for absorption. The ciliated cells are also protective in that the beating ciliary action works against large-particle deposition. 

The trachea and bronchi likewise have a protective function. Mucous and serous cells secrete fluids that together comprise the mucus, which is moved toward the pharynx by the cilia of the ciliated cells. The movement of mucus serves to move entrapped particles toward the pharynx where they are eliminated by swallowing or expectoration. The mucus may also have other protective functions, protecting the epithelial cells by free radical scavenging and antioxidant properties. The Clara cells are known to contain high concentrations of xenobiotic metabolizing enzymes. 

Chailley, B. Nicolas, G. and Laine, M. C. (1989) Organization of actin microfilaments in the apical border of oviduct ciliated cells. Biology of the Cell 67 81-90... 

Conducting airways Trachea 0 20-18 Pseudostrati fled cell Ciliated cell Columnar cell Goblet cell Serous cell Mucous cell 20-40... 

There are approximately 200 cilia on each ciliated cell. They are packed at a density of 6-8 cilia per m2 and cannot move without affecting neighbouring cilia. In order to perform an unhindered beat cycle the movement of each cilium is slightly out of phase with that of its neighbor, leading to a phenomenon termed ciliary metachrony . Metachrony results solely from hydrodynamic coupling between adjacent cilia and provides the necessary cooperation within a field of cilia to permit them to transport mucus. 

Ciliated cells have small membranous projections (cilia) that contain interior contractile proteins cilia beat in synchrony and serve to sweep away foreign particles on the surface of the respiratory tract, i.e., in the lungs and the nasal lining. 

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