Trachea Diffusion of oxygen and carbon dioxide takes place across the walls of the smallest tubes, called tracheoles, which penetrate tissues and even indent individual cells. Gas may be conducted through the respiratory system by means of active ventilation or passive diffusion. Unlike vertebrates, insects do not generally carry oxygen in their haemolymph. This is one of the factors that may limit their size. A tracheal tube may contain ridge-like circumferential rings of taenidia in various geometries such as loops or helices. Taenidia provide strength and flexibility to the trachea. In the head, thorax, or abdomen, tracheae may also be connected
The Human Body (TV series) programmes on the human body. The series was produced by Richard Dale and presented by Professor Robert Winston, a fertility expert. The series used a variety of different techniques to present the topics being discussed, including endoscopes and computer graphics for internal shots, time-lapse photography to show the growth of hair and nails, magnetic resonance imaging and scanning electron microscopy. The series gained 6.3 million viewers and an audience share of 38%. The series was nominated for numerous awards, winning several, including three BAFTA awards, four RTS awards and a Peabody Award. A DVD of the series was released in