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) The Human Body (TV series) The Human Body is a seven-part documentary series, first shown on 20 May 1998 on BBC One and presented by medical scientist Robert Winston. A co-production between the BBC and The Learning Channel, the series looks at the mechanics and emotions of the human body from birth to death. The series was nominated for numerous awards, winning several, including three BAFTA awards, four RTS awards and a Peabody Award. Described as the BBC's "first major TV series on human biology", it took over two years to make and aimed to be the definitive set of