Trachea into left and right main bronchi. The trachea begins level with the sixth cervical vertebra and the carina is found at the level of the fifth thoracic vertebra (T5), opposite the sternal angle and can be positioned up to two vertebrae lower or higher, depending on breathing. The trachea is surrounded by rings of hyaline cartilage; these rings are incomplete and C-shaped. The cricoid cartilage is attached to the first tracheal ring at top of the trachea and acts as the bottom of the larynx. There are fifteen to twenty rings in total, separated by narrow intervals. These reinforce the
Effect of spaceflight on the human body space propulsion systems have been examined for over a century, and millions of man-hours of research have been spent on them. In recent years there has been an increase in research on the issue of how humans can survive and work in space for extended and possibly indefinite periods of time. This question requires input from the physical and biological sciences and has now become the greatest challenge (other than funding) facing human space exploration. A fundamental step in overcoming this challenge is trying to understand the effects and impact of long-term space travel on the human body. In October