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Smoking exposes delicate cells inside the lungs directly to these compounds. This causes mutations in the DNA of the cells, which leads to cancer. According to the World Health Organization's report, "Tobacco Smoke and Involuntary Smoking", 80 percent of all cases of lung cancer are attributable to smoking.
The cilia are hair-like, microtubular-based structures on the luminal surface of the epithelium. On each epithelial cell there are around 200 cilia that beat constantly at a rate of between 10 and 20 times per second. The cilia are surrounded by a periciliary liquid layer (PCL), a sol layer that is overlain with the gel layer of mucus. [9]
The epithelial lining of the upper respiratory tract is interspersed with goblet cells that secrete a protective mucus. This helps to filter waste, which is eventually either swallowed into the highly acidic stomach environment or expelled via spitting. The epithelium lining the respiratory tract is covered in small hairs called cilia.
Cilia Structure. Primary cilia are found to be formed when a cell exits the cell cycle. [2] Cilia consist of four main compartments: the basal body at the base, the transition zone, the axenome which is an arrangement of nine doublet microtubules and considered to be the core of the cilium, and the ciliary membrane. [2]
A ciliopathy is any genetic disorder that affects the cellular cilia or the cilia anchoring structures, the basal bodies, [1] or ciliary function. [2] Primary cilia are important in guiding the process of development, so abnormal ciliary function while an embryo is developing can lead to a set of malformations that can occur regardless of the particular genetic problem. [3]
Though smoking leads to an overall decrease in DNA methylation, several critical genes become hypermethylated. Two of the most noteworthy of these genes are p16 and p53. These genes are critical to cell cycle regulation and were shown to have higher levels of methylation in smokers than in non smokers. [3]
Mammals also have motile cilia or secondary cilia that are usually present on a cell's surface in large numbers (multiciliate), and beat in coordinated metachronal waves. [40] Multiciliated cells are found lining the respiratory tract where they function in mucociliary clearance sweeping mucus containing debris away from the lungs . [ 13 ]
Another important cell type is the pulmonary neuroendocrine cell. These are innervated cells that only make up around 0.5% of the respiratory epithelial cells. [7] The ciliated cells are columnar epithelial cells with specialized ciliary modifications. The ciliated cells make up between 50 and 80 per cent of the epithelium. [8]