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
Unethical human experimentation in the United States ashes analyzed for radioisotopes. This project was kept secret primarily because it would be a public relations disaster; as a result parents and family were not told what was being done with the body parts of their relatives. Between 1960 and 1971, the Department of Defense funded non-consensual whole body radiation experiments on mostly poor and black cancer patients, who were not told what was being done to them. Patients were told that they were receiving a "treatment" that might cure their cancer, but the Pentagon was trying to determine the effects of high levels of radiation on the human