Ciliated epithelial cells

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. 

Nonciliated cells separate fields of ciliated epithelial cells from each other. Synchronized ciliary movement, with a beat frequency in human proximal airways under normal conditions of 8-15 EIz, propels mucus along the mucociliary escalator at a rate of up to 25 mm/min. Beat frequencies appear to slow to roughly 7 Hz in more distal airways. Cilia move in the same direction and in phase within each field but cilia in adjacent fields move in slightly different directions and are phase shifted. These beat patterns result in metachronal waves that steadily move mucus at higher velocities ( -12-18 mm/min) than would be achievable by summing the motion of individual cilia. 

The prediction of such hot spots of gas transfer at bifurcations is supported by experimental data on ozone-exposed rabbits. Longitudinal slices of airways from these rabbits showed at low magnification that desquamation of the ciliated epithelial cells was focal and sometimes more intense at a bifurcation. 

In some cases, cells in a persistently stressful environment may be replaced by a cell type that is better able to withstand the harsh environment. Replacement of an adult cell type by another adult cell type is known as metaplasia and is usually a reversible change. Perhaps the best-known example of metaplasia is the replacement of the normally tall (columnar), ciliated epithelial cells in the respiratory tract of cigarette smokers by layers of relatively flattened (squamous) epithelial cells. While the squamous epithelial cells are somewhat tougher than the columnar cells, important functions such as mucus secretion are lost. In addition, the continued stresses that induce metaplasia may lead to neoplastic transformation. 

Acetylcholine is the neurotransmitter at all these sites, acting on a postsynaptic receptor, except on most blood vessels in which the action of cholinergic drugs is unrelated to cholinergic vasodilator nerves. It is also produced in tissues unrelated to nerve endings, e.g. placenta and ciliated epithelial cells, where it acts as a local hormone (autacoid) on local receptors. 

Brush Transitional form of ciliated epithelial cell... 

The mucociliary escalator functions when inhaled particles between 2 to 10 pm are deposited on the sticky mucous lining of the tracheobronchial tree and are propelled upward by the movement of this mucous layer in response to the beat of the cilia on the ciliated epithelial cells. This phenomenon is made possible because the mucous layer is biphasic, consisting of a watery solution in direct contact with the epithelia cells in which the cilia are free to beat. This watery solution is covered by a stickier, more adhesive gel layer that can trap and hold inhaled particles. The cilia beat in the wall layer at a rate between 1000 and 1500 strokes per minute such that at the point of their maximum upward velocity, the tips of the cilia come in contact with the gel layer to propel it upward. All recovery strokes subsequently occur in the water layer. This mechanism moves the mucus upward at a rate between 1 and 3 cm/minute. Ultimately, the mucus reaches the pharynx, where it is swallowed. Disease states that either alter the mucus-producing properties of cells in the tracheobronchial tree or decrease ciliary activity will obviously have a deleterious effect on this important clearance mechanism. 

A variety of human cells have cilia and flagella, hairlike projections from the surface that have a strokelike motion. These projections contain a flexible organized array of microtubules. Fluid or mucus is propelled over the surface of ciliated epithelial cells by the coordinated beating of cilia. A sperm cell swims by means of a flagellum. 

Terbutaline, (RS)-2-ferf-butylamino-l-(3,5-dihydro-xyphenyl)ethanol, and isoprenaline increased im-munoreactive cAMP in ciliated epithelial cells of dog and cat trachea and in both serous and mucous gland cells of cat trachea (Lazarus et al. 1984). Epithelial goblet cells did not respond to P-adrenergic agonists in either species. 

Fig. 85. Bronchiolar ciliated epithelial cell showing membrane bound vesicles between the axonema and the ciliary membrane. Lung of a female rat (No. 4 breeder Winkebnann, Borchen-Kirchborchen) which had inhaled 10 mg powdered Grangesberg magnetite/m3 4 h per day, 5 days per week from August 24 to October 19, 1967 for a total of 40 days. Fixed on January 15, 1968 under methitural anaesthesia by intratracheal instillation of 2.5 % glutaraldehyde in phosphate buffer (pH 7.4) before opening the thorax. Postfixation with 1 % osmium tetroxide in phosphate buffer (pH 7.4). Contrasted en bloc for 12 h with 0.5% uranyl acetate in 70% ethanol. Embedded in a 2 8 mixture of methyl and butyl methacrylate. Sectioned at 50 nm. Lead citrate after Reynolds (1963). Film 33131...

In megakaryocytes there may be as many as 40 pairs of centrioles (Fawcett, 1966). In the differentiation of ciliated epithelial cells the centrioles reduplicate to form several hundred basal bodies, giving rise to cilia and serving as their kinetic centers. Centrioles are hollow cylinders 300-500 nm in length and 150 nm in diameter. Their walls are composed of nine evenly-spaced, triplet, hollow fibrils or tubules embed-... 

The ciliated epithelial cells extend down the respiratory tract to the respiratory bronchioles. The cilia provide locomotion for the overlying mucous blanket, propelling mucus and associated debris forward in the most anterior portion of the nares or propelling it to the oral cavity in the most posterior portion of the nasopharyngeal compartment. In the tracheobronchial compartment, mucus and associated material are moved upward to the oral cavity. 

Figure 7 Diagram of mucous blanket of the conducting airways Although the exact structure of the mucous layer of the airways is unknown, the diagram shows some of the features that have been demonstrated in recent light and electron microscopic studies. An osmiophilic film is seen at the air-liquid interface, which has a multilaminated appearance and exists in various degrees of thickness (see inset). Beneath this surfactant film lies an aqueous hypophase, again of variable thickness, in which are found macrophages, mucus, and osmiophilic lamellar structures. CC, Clara cell CEP, ciliated epithelial cell GC, goblet cell.

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