Trachea are generally highly elastic but they may calcify with age. The trachealis muscle connects the ends of the incomplete rings and contracts during coughing, reducing the size of the lumen of the trachea to increase the rate of air flow. The esophagus lies posteriorly to the trachea, adjoining along the tracheoesophageal stripe. Circular horizontal bands of fibrous tissue called the annular ligaments of trachea join the tracheal rings together. The cartilaginous rings are incomplete to allow the trachea to collapse slightly so that food can pass down the esophagus. A flap-like epiglottis closes the opening to the larynx during swallowing
Traditional Chinese medicines derived from the human body centuries after Li Shizhen considered the bioethical and biomedical dilemmas of using human drugs, 20th-century technological and medical advances have raised new related questions of organ transplants, transplantation medicine, organ trade, tissue banks, human cloning, and the commodification of human body parts (Awaya 1999, Nie 2002, Scheper-Hughes and Wacquant 2002). Traditional Chinese medicines derived from the human body Li Shizhen's (1597) "Bencao gangmu", the classic materia medica of traditional Chinese medicine (TCM), included 35 human drugs, including organs, bodily fluids, and excreta. Crude drugs derived from the human body were commonplace in the early history of medicine. Some of these