The cartilage rings are C-shaped because the back of the trachea presses against the esophagus. The cartilage opens at the esophagus and is replaced by connective tissue and muscle. This gives the esophagus space to allow food to be swallowed easily. The rings of the trachea are stacked one on top of the other, with a small space between them.
In 2014, a survey of the Australian working population revealed that the most common carcinogenic exposures in the workplace were solar ultraviolet radiation, diesel engine exhaust, environmental tobacco (second-hand) smoke, benzene, lead and silica.
The three most common forms of skin cancer are: Basal cell carcinoma (BCC). The most common skin cancer and the most frequent cancer in humans, BCC affects more than 1 million people each year in the United States. BCC develops in the basal cells that make up the deepest layer of the epidermis, the top layer of the skin.