09 .Metaplasia of laryngeal respiratory epithelium has occurred here in a smoker. The chronic irritation has led to an exchanging of one type of epithelium (the normal  respiratory epithelium at the right) for another (the more resilient squamous epithelium at the left). Metaplasia is not a normal physiologic process and may be the firststep toward neoplasia

09.图示吸烟患者喉部呼吸上皮的化生。慢性刺激导致一种上皮（右边的正常呼吸上皮）向另一种上皮（左边更富弹性的鳞状上皮）转变。化生不是一种正常的生理性过程，而可能是形成肿瘤的第一步。