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
Human body temperature change according to activities and external factors. In addition to varying throughout the day, normal body temperature may also differ as much as from one day to the next, so that the highest or lowest temperatures on one day will not always exactly match the highest or lowest temperatures on the next day. Normal human body temperature varies slightly from person to person and by the time of day. Consequently, each type of measurement has a range of normal temperatures. The range for normal human body temperatures, taken orally, is (). This means that any oral temperature between is likely